4^. 


LIBRARIES 


Date  Due 


•gfiir^' 


^IVlr2a 


I7r^,r, 


C^^  V'V 


,b28'3^ 


iki^ 


5StJp34 


juiUi, 


i2^  *^ 


31May'38 


AGRICULTURAL  AND  BIOLOGICAL  PUBLICATIONS 
CHARLES  V.  PIPER,  Consulting  Editor 


THE  FUNDAMENTALS 

OF 

FRUIT  PRODUCTION 


UMMiMl^ai^!!!")  lHHLU,U>a^^^^ 


!^  Qraw-7J ill  Book  (h  Im 

PUBLISHERS     OF     BOOKS      F  O  P_^ 

Coal  Age  ^  Electric  Railway  Journal 
Electrical  World  v  Engineering  News-Record 
American  Machinist  v  Ingenieria  Internacional 
Engineering 8 Mining  Journal  "^  Power 
Chemical  S  Metallurgical  Engineering 
Electrical  Merchandising 


ImlTTnlltTlTTTlTlMm 


THE  FUNDAMENTALS 

OF 

FRUIT  PRODUCTION 


BY 

VICTOR  RAY  GARDNER 
FREDERICK  CHARLES  BRADFORD 

AND 

HENRY  DAGGETT  HOOKER,  JR. 

OF   THE    department' OF   HORTICULTURE    OF   THE    UNIVERSITY    OF   MISSOURI 


First  Edition 


McGRAW-HILL  BOOK  COMPANY,  Inc. 
NEW  YORK:  370  SEVENTH  AVENUE 

LONDON:  6&  8  BOUVERIE  ST.,  E.  C.  4 

1922 


4lp 


Copyright,  1922,  by  the 
McGraw-Hill  Book  Company,  Inc. 


THE     MA.FI<B     PRESS     YORK    Pj 


UBMMY 

N.  C.  State  College 

PREFACE 

Fruit  growing  in  the  United  States  is  so  widespread  and  so  diversified 
that  no  work  of  ordinary  dimensions  can  codify  it  on  the  basis  of  empirical 
practices,  which  differ  from  place  to  place.  The  fundamental  factors, 
however,  are  always  the  same  and  once  they  are  understood,  the  adapta- 
tion of  practices  to  local  conditions  presents  Httle  difficulty. 

The  present  work  attempts  to  focus  attention  on  the  conditions 
which  make  the  fruit  plant  profitable;  practices  are  considered  only  as 
they  affect  these  conditions,  not  as  ends  in  themselves.  Maintenance 
of  this  point  of  view  has  necessitated  a  rather  wide  departure  from  con- 
ventional arrangement  of  subject  matter.  The  common  orchard  prac- 
tices are  not  sacred  in  themselves;  indeed,  they  are  important  only  in  so 
far  as  they  help  vegetative  growth  and  especially  fruit  production. 
Fundamentally  the  plant's  growth  and  functioning  depend  on  the  nature 
of  the  environment  and  the  adjustment  thereto  and  not  directly  on  cul- 
tural practices,  which  only  modify  the  relation  of  the  plant  to  the  environ- 
mental complex.  Consequently  these  practices  appear  inconspicuous  in 
the  Chapter  and  Section  headings. 

Acquaintance  with  principles  without  the  facts  on  which  they  rest 
is  itself  empirical.  Particular  attention,  therefore,  is  given  to  the 
inclusion  of  sufficient  illustrative  matter  to  permit  quantitative  estimate 
of  the  validity  and  applicability  of  the  principles  enunciated.  Com- 
paratively little  that  is  original  is  presented;  much  of  the  material  that  is 
novel  to  pomological  texts  is  included  because  of  its  inaccessibility  to  the 
average  student.  Many  significant  observations  which  have  been  neg- 
lected because  their  ultimate  bearing  was  not  appreciated  at  the  time 
they  were  recorded,  have  been  reviewed  in  the  light  of  modern  knowledge. 
Plant  physiology,  plant  chemistry,  soil  science  and  physics  have  been 
requisitioned  freely  and  advisedly;  in  no  case,  however,  without  an  indi- 
cation of  applicability  to  pomology.  Careful  consideration  has  approved 
this  course  because  special  applications  to  fruit  growing  are  rare  in  the 
general  University  courses  in  these  subjects  and  because  in  the  arrange- 
ment of  many  curricula,  pomology  precedes  some  of  the  science  courses 
which  are  needed  as  preparatory  training.  Though  every  effort  is  made 
to  insure  thoroughness,  exhaustive  treatment  is  not  attempted,  since  it 
would  be  useful  to  few  readers. 

The  solution  of  a  problem  arising  outside  of  the  classroom  depends  on 
obtaining  all  the  pertinent  data,  systematizing  them  to  ascertain  the 
factors  involved  and  ^.pplying  to  the  problem  th,e  knowledge  so  gained. 

v 

118x0 


vi  PREFACE 

This  text  is  designed  to  prepare  the  student  to  undertake  these  steps. 
As  with  any  text,  much  is  necessarily  left  to  the  instructor,  particularly 
matters  of  opinion  and  of  local  application. 

Finally,  it  hardly  need  be  said  that  this  text  is  intended  for  students 
of  college  grade.  It  is  not  a  manual  on  how  to  grow  fruit;  it  does  not 
attempt  to  enter  fields  best  covered  by  classroom  discussion,  laboratory 
work  or  practical  experience.  It  is  intended,  however,  to  be  a  supple- 
ment and  guide  to  these. 

The  writers  wish  to  express  their  appreciation  of  the  helpful  criticisms 
and  suggestions  offered  by  those  to  whom  portions  of  this  manuscript 
have  been  submitted:  to  Dr.  M.  M.  McCool  of  the  Michigan  Agricultural 
Experiment  Station  (the  Section  on  Water  Relations);  to  Dr.  William 
Crocker  of  the  University  of  Chicago  and  to  Dr.  E.  J.  Kraus  of  the 
University  of  Wisconsin  (the  Section  on  Nutrition) ;  to  Dr.  W.  H.  Chand- 
ler of  Cornell  University  (Chapters  14-18,  dealing  with  Winter  Injury); 
to  Dr.  O.  M.  Stewart,  Professor  of  Physics  in  the  University  of  Missouri 
and  to  George  Reeder  of  the  U.  S.  Weather  Bureau  (Chapters  19  and  20 
on  Frost  Occurrence  and  Control) ;  to  Prof.  Ray  Roberts  of  the  University 
of  Wisconsin  (the  Section  on  Pruning) ;  to  Dr.  M.  J.  Dorsey  of  the  Uni- 
versity of  Minnesota  (the  Section  on  Fruit  Setting) ;  to  Prof.  W.  P.  Tufts 
of  the  University  of  California,  to  Dr.  J.  K.  Shaw  of  the  Massachusetts 
Agricultural  Experiment  Station  and  to  Paul  C.  Stark  of  the  Stark  Bros. 
Nursery  Co.  (the  Section  on  Propagation) ;  to  Prof.  Roy  E.  Marshall  of 
the  Michigan  Agricultural  College  and  to  Prof.  W.  P.  Tufts  of  the  Uni- 
versity of  Cahfornia  (Chapters  34  and  35  on  Orchard  Locations  and 
Soils);  finally  to  Dr.  C.  V.  Piper.  Many  valuable  criticisms  and  sug- 
gestions have  been  incorporated  in  the  text.  In  a  few  instances  the 
writers  have  believed  themselves  justified  in  adhering  to  their  original 
interpretations  of  the  evidence,  so  that  these  authorities  who  have 
assisted  the  writers  very  materially  are  not  to  be  held  responsible  for 
any  part  of  the  book  in  its  present  form. 

Acknowledgment  is  made  also  to  Prof.  C.  E.  Shuster  of  the  Oregon 
Agricultural  Experiment  Station  for  Figures  and  to  Dr.  J.  K.  Shaw  of  the 
Massachusetts  Agricultural  Experiment  Station  for  Figure  56. 

Columbia,  Mo.  The  AUTHORS. 

August,  1921. 


CONTENTS 

Preface    


SECTION  I 
Water  Relations 

CHAPTER  I 

The  Water  Requirements  of  Fruit  Plants 3 

Water  as  a  Plant  Constituent — The  Water  Requirements  of  Plants  in  Terms 
of  Dry  Weight — The  Water  Requirements  of  Plants  in  Terms  of  Precipita- 
tion— Amounts  Used  by  the  Plants  Themselves;  Total  Amounts  Required 
for  Plants  and  to  Compensate  for  Evaporation,  Runoff  and  Seepage — Plant- 
ing Distances  Related  to  Moisture  Supply — Factors  Influencing  the  Water 
Requirements  of  Plants — Nutrient  Supply;  Cultivation;  Light;  in  General; 
Some  Applications  to  Practice — The  Wilting  Point  for  Fruit  Plants — Wilting 
Coefficients;  Wilting  under  Field  Conditions;  _  Wilting  Coefficients  and 
Drought  Resistance — Summary. 

CHAPTER  II 

The  Intake  and  Utilization  of  Water 18 

Water  Absorption — The  Water  Absorbing  Organs — The  Handling  and 
Transplanting  of  Nursery  Stock — The  Water  Absorbing  Process — Factors 
Enabling  the  Roots  to  Exploit  the  Soil;  Adaptation  of  Roots  to  Moisture 
Conditions;  Factors  Influencing  Rate  of  Absorption;  Submergence  and  Root 
Killing — Transpiration — Cuticular  and  Stomatal  Transpiration  Compared; 
Variability  in  Number  of  Stomata  in  Accordance  with  External  Conditions — 
Factors  Influencing  Rate  of  Transpiration — Character  of  Cuticle;  Age  of 
Leaf;  Defoliation,  Summer  Pruning;  Wind  Velocity,  Windbreaks;  Light; 
Temperature,  Slope  of  Ground — The  Water  Conducting  System  of  the  Tree 
— Summary. 

CHAPTER  III 

Orchard  Soil  Management  Methods  and  Moisture  Conservation  ...  31 
Orchard  Soil  Management  Methods  Defined  and  Described — Orchard  Soil 
Management  Methods  and  Surface  Run-ofi' — Moisture  Under  Tillage  and 
Sod-Mulch  Systems  of  Management — Some  New  York  and  Pennsjdvania 
Records;  Some  New  Hampshire  Records;  English  Experience;  Some 
Kentucky  and  Kansas  Records;  in  General;  Practicability  of  Sod-mulch 
System  Influenced  by  Depth  of  Rooting — Influence  of  Depth  and  Frequency 
of  Cultivation  upon  Soil  Moisture — Intercrops  and  the  Soil  Moisture  Supply 
—Cover  Crops  and  the  Moisture  Supply — Efi'ects  of  Early  and  Late  Seeding; 
Winter-killed  and  Winter-surviving  Cover  Crops — Wind  Velocity  and 
Evaporation,  Windbreaks — Summary. 

vii 


viii  CONTENTS 

CHAPTER  IV 

Paob 
Soil  Moisture:  Its  Classification,   Movement  and  Influence  on  Root 

Distribution 47 

Classification  of  the  Water  in  Soils  and  Plant  Tissues — The  Response  of 
Water  to  the  Force  of  Gravity  and  the  Evaporating  Power  of  the  Air; 
the  Relative  Saturation;  Resistance  to  Freezing — Movement  of  Water  in  the 
Soil — Percolation;  the  Rise  of  Water  by  Capillarity;  Lateral  Movement  of 
Water  in  the  Soil — The  Distribution  of  Fruit  Tree  Roots  as  Influenced  by  Soil 
Moisture — The  Idea^  Root  System — Specific  and  Varietal  Differences  in  Root 
Distribution — The  Distribution  of  Tree  Roots  under  Varying  Conditions — 
In  the  Hood  River  Valley,  Oregon  and  in  Ohio ;  in  a  Gravelly  Loam,  Underlaid 
by  Hardpan,  in  Maine;  in  a  Thin  Gravelly  Loam,  Underlaid  by  Rock,  in 
Maine;  in  Dwarfs;  the  Influence  of  Soil  Moisture;  the  Influence  of  Culti- 
vation; the  Influence  of  Soil  "Alkali" — Applications  to  Orchard  Practice — 
Summary. 

CHAPTER  V 

The  Response  of  Fruit  Plants  to  Varying  Conditions  of  Soil  Moisture 

AND  Humidity 66 

Influence  of  Soil  Moisture  on  Vegetative  Growth— New  Shoots  and  their 
Leaves;  Annual  Rings  and  Trunk  Circumference;  Moisture  Supply  and  the 
Growth  Period  in  Early  Spring;  the  "Second  Growth  "  of  Midsummer  or  Late 
Summer — Influence  of  Water  Supply  on  the  Development  of  Fruit — Size; 
Yield;  Shape  and  Color;  Composition;  Disease  Resistance  and  SusceptibiHty 
— Residual  Effects  of  Soil  Moisture — On  Vegetative  Growth;  on  Yields — 
Influence  of  Atmospheric  Moisture  on  Growth — In  General;  Russeting  of 
Fruit;  Fruit  Setting — Summary. 

CHAPTER  VI 

Pathological  Conditions  Associated  with  Excesses  and  Deficiencies  in 

Moisture 83 

Disturbances  Due  to  Moisture  Excesses — The  Splitting  of  Fruit;  (Edema; 
Fasciation  and  Phyllody;  Chlorosis;  Rough  Bark  or  Scaly  Bark  Disease; 
Watercore — Disturbances  Due  to  Moisture  Deficiencies — Defoliation, 
Premature  Ripening  of  Wood — Dieback — Cork,  Drought  Spot  and  Related 
Diseases — Fruit-pit;  Cork;  Surface  Drought  Spot;  Deep-seated  Drought 
Spot;  Dieback  and  Rosette;  Bitter-pit;  Jonathan-spot;  Black-end — Silver 
Leaf — Lithiasis — Summary. 

SECTION  II 

Nutrition 

CHAPTER  VII 

Plant  Nutrients  and  Their  Absorption 101 

Distribution  of  Elements  Found  in  Ash — In  Tissues  of  Different  Kinds;  in 
Tissues  of  Different  Age;  at  Different  Seasons — Absorption — The  Osmotic 
System — Displacement — Availability  of  Ash  Constituents — Availability 
and  Solubility  Distinguished;  Factors  Influencing  Solubility;  Availability  of 


CONTENTS  IX 

Page 
Phosphorus;  Availabihty  Varies  According  to  Ivind  of  Plant;  Availability  of 
Iron  and  Sulfur — Availabihty  of  Nitrogen — Nitrification — Aided  by  Liming; 
Influenced  by  Methods  of  Soil  Management;  Influenced  by  Temperature  and 
Soil  Moisture — Losses  of  Nitrogen  from  the  Soil — Maintaining  the  Nitrogen 
Supply  of  the  Soil — Nitrogen  Fixation— Soil  Reaction,  Acidity  and 
Alkahnity — Soil  Reaction  and  the  Availability  of  Phosphorus;  Soil  Reaction 
and  the  Availability  Of  Iron;  Acid  Tolerance  of  Certain  Crops — Concent- 
ration, Soil  "Alkah" — Tolerance  of  Different  Fruits;  Injuries  from  Excessive 
Fertilization;  some  effects  of  Soil  Alkali;  Remedial  Measures — Soil  Toxicity 
— General  and  Specific  Effects;  Protecting  Against  Toxins;  Importance  in 
the  Fruit  Plantation — Antagonism;  Aeration;  Selective  Absorption — 
Transpiration — The  Nutrient  Requirements  of  Crop  and  Fruit  Plants — 
Summary. 

CHAPTER  VIII 

Individual.  Elements 130 

Nitrogen — Synthesis  of  Organic  Nitrogenous  Compounds — Translocation 
and  Use  of  Elaborated  Nitrogenous  Compounds — Seasonal  Distribution  of 
Nitrogen — In  Leaves;  in  Branches,  Trunks  and  Roots;  in  Spurs;  in  Fru't;  in 
Various  Tissues  of  Trees  of  Different  Age — Phosphorus — Synthesis  of  Phos- 
phorus-contain'ng  Orgaific  Compounds — Translocation  and  Use  of  Phos- 
phorous-containing Compounds — Amounts  Used  in  Fruit  Production — 
Seasonal  Distribution  of  Phosphorus — In  Leaves;  in  Branches,  Trunk  and 
Roots ;  in  Spurs ;  in  Fruit ;  in  Various  Tissues  of  Trees  of  Different  Ages — Potas- 
sium— Synthesis,  Translocation  and  use  of  Potassium-containing  Compounds 
— The  Demand  and  the  Supply — Seasonal  Distribution  of  Potassium — 
In  Leaves;  in  Branches,  Roots  and  Trunks;  in  Spurs;  in  Fruit;  in  Various  Tis- 
sues of  Trees  of  Different  Age — Sulfur — Iron — Magnesium — Calcium — 
Seasonal  Distribution  of  Calcium — In  Buds  and  Leaves;  in  Bark  and  Wood; 
In  Fruits — The  Demand  and  the  Supply — Other  Mineral  Elements — Silicon; 
Sodium;  Chlorine;  Aluminum  and  Manganese — Summary. 

CHAPTER  IX 

Manufacture  and  Utilization  op  Carbohydrates 161 

Assimilation  and  Limiting  Factors  Defined — Carbon  Assimilation — Factors 
Involved — Carbon  Dioxide;  Water;  Light — Leaf  Pigments — Variation  with 
Age;  Variation  with  Light  Supply — Temperature;  Enzymes — Products 
— Oxygen- — Carbohydrates — Daily  and  Seasonal  Fluctuation  in  Leaves; 
Forms  of  Storage — Seasonal  Fluctuations  of  Stored  Carbohydrates — Easily 
Hydrolizable  Carbohydrates;  Starch;  Sugars — Carbohydrate  Utilization — • 
In  Tissue  Building;  in  Retaining  Moisture;  Increasing  Osmotic  Concentra- 
tion; as  a  Source  of  Energy;  Relation  to  Pigment  Formation — Summary. 

CHAPTER  X 

The  Initiation  of  the  Reproductive  Processes .    181 

The  Development  of  the  Fruitful  Condition — The  Response  of  the  Plant 
to  Changes  in  Relative  Amounts  of  Nitrogen  and  of  Carbohydrates — The 
Significance  of  Carbohydrate  Accumulation,  Manufacture  in  Excess  of 
Utilization — In  Fruit  Spurs;  Influence  of  the  Nitrate  Supply;  Influence  of  the 
Moisture    Supp'y;    Influence    of    Other    Factors — Fruit-bud    Formation — 


CONTENTS 

Page 
Evidence  of  Differentiation— Time  of  Differentiation — In  Relation  to  Posi- 
tion; Varietal  Differences;  Differences  Induced  by  Cultural  Treatment — 
Abnormalities;  Winter  Stages — Summary. 


CHAPTER  XI 

Surpluses  and  Deficiencies 194 

Surpluses — Nitrogen;  Magnesium;  Copper;  Arsenic;  Manganese;  Other 
Elements — Deficiencies — Nitrogen;  Phosphorus  and  Potassium;  Sulfur; 
Iron;  Magnesium  and  Calcium;  Chlorine — Analysis  of  the  Fertilizer  Problem 
— The  FertiHzer  Requirements  of  the  Orchard. 


CHAPTER  XII 

The  Application  of  Nitrogen-carrying  Fertilizers 204 

The  Influence  of  Nitrogenous  Fertilizers  on  Vegetative  Growth — In  Peaches; 
in  Apples;  in  Strawberries;  Negative  Results,  Nitrogen  not  a  Limiting 
Factor — Influence  of  Nitrogen  on  Blossom-bud  Formation — in  Peaches;  in 
Apples — Influence  of  Nitrogen  on  the  Setting  of  Fruit — Influence  of  Nitro- 
gen on  Size  of  Fruit — Influence  of  Nitrogen  on  Coior  of  Fruit — Influence  of 
Nitrogen  on  Yield — The  Correlation  Between  Vegetative  Growth  and 
Yield — Influence  of  Nitrogen  on  Composition  and  on  Season  of  Maturity — 
Summary. 

CHAPTER  XIII 

Fertilizers,  Other  Than  Nitrogenous,  in  the  Orchard 218 

The  Indirect  Effects  of  Fertilizers — Phosphoric  Acid;  Sulfur;  Lime — 
Plant  Nutrient  Carriers,  Different  Forms  of  Fertilizers — Nitrogen  from 
Inorganic  Sources;  Nitrogen  from  Organic  Sources;  Phosphorus;  Potassium; 
Sulfur;  Lime — Season  for  Applying  Fertilizers — The  Relations  of  Seasonal 
Conditions  to  Response  From  Fertilizers — Summary. 


SECTION  III 

Temperature  Relations  of  Fruit  Plants 

CHAPTER  XIV 

Growing  Season  Temperatures 236 

Heat  Units — The  Relative  Values  of  Different  Effective  Temperatures — 
Influence  of  Latitude  on  Heat  Requirements — In  the  Early  Harvest  Apple; 
in  the  Elberta  Peach;  in  Chestnut  Blight — Variations  in  Heat  Requirements 
from  Season  to  Season — Acclimatization  to  Varying  Amounts  of  Heat — In 
General — Optimum  Temperatures— Variation  within  the  Species  or  Variety; 
Differences  within  the  Variety  for  Separate  Processes;  Variation  in  Quality 
with  Amount  of  Summer  Heat;  Variation  in  Season  of  Maturity  with 
Amount  of  Summer  Heat — Soil  Temperatures — Indirect  Temperature 
Effects — Summ  ary . 


CONTENTS  xi 

CHAPTER  XV 

Page 

Winter  Killing  and  Hardiness 250 

Death  from  Freezing — Tissue  Freezing  is  Accompanied  by  Cell  Dehydration; 
Freezing,  Not  Cold,  Ivills;  Freezing  and  the  Deciduous  Habit — Increasing 
Hardiness — By  Increasing  Sap  Density — By  Increasing  Water-retaining 
Capacity — Water-retaining  Capacity  Associated  with  Pentosan  Content — 
Water  Soluble  Pentosans  in  Particular — Pentosan  Content,  Water-retaining 
Capacity  and  Hardiness  Responsive  to  Environmental  Conditions — In- 
creased Hardiness  with  Increased  Maturity — Rapid  Temperature  Changes 
— Killing  with  Slow  and  with  Rapid  Freezing;  Slow  and  Rapid  Thawing — 
Variation  in  Critical  Temperatures — Summary. 

CHAPTER  XVI 

Winter  Injury 264 

Conditions  Accompany  Winter  Injury;  Winter  Injuries  Classified — Injuries 
Associated  with  Immaturity — Affecting  More  or  Less  the  Entire  Plant — 
Tender  Plants  May  be  More  Resistant  Than  Hardier  Plants;  the  Effect  of 
Summer  Conditions  Favorable  for  Late  Growth;  Second  Growth  Particularly 
Susceptible;  Preventive  Measures — Localized  Injuries — Crotch  and  Crown 
Injury;  Locahzed  Injuries  and  Delayed  Maturity;  Contributing  Factors; 
Remedial  Measures — Wiitter  Injury  Associated  with  Drought — Immaturity 
and  Winter  Drought — Water  Loss  from  Dormant  Tissues — Water  Conduc- 
tion in  Trees  durmg  the  Winter — Relation  of  Freezing  to  Water  Conduction 
— Where  Winter  Drought  Conditions  Prevail — Protection  against  Winter 
Drought  Injuries — Winter  Irrigation — Cultivation;  Cover  Crops  — 
Windbreaks — Effect  of  Wind  Velocity;  Effect  on  Evaporation;  Effect  on  Soil 
Moisture — Injuries  Characteristic  of  Late  Winter  Conditions — The  Rest 
Period — Injuries  to  Fruit  Buds — Changes  in  Water  Content  of  Buds  during 
Winter^Contributing  Factors — Protective  Measures — Pruning;  Fertiliza- 
tion and  Cultivation;  Thinning;  Whitewashing  and  Shading — In  General — 
Injuries  to  Vegetative  Tissues — Distinguished  from  Summer  Sunscald  and 
Injuries  Associated  with  Immaturity;  Moisture  and  Temperature  Condi- 
tions in  the  Affected  Parts;  Preventive  Measures — Injuries  Due  to  Sudden 
Cold — General  Effects;  Trunk  Splitting — Summary. 

CHAPTER  XVII 

Winter  Injury  to  the  Roots 302 

Soil  Temperatures  in  Winter;  Critical  Temperatures  for  Tree  Roots — Factors 
Influencing  Frost  Penetration — Protection  Afforded  by  Snow;  Different  Sys- 
tems of  Soil  Management;  Soil  Type;  Soil  Moisture — Relation  of  Cover 
Crops  to  Root  Killing — Root  Killing  in  Different  Fruits — The  Apple;  the 
Pear;  the  Peach;  the  Cherry;  the  Plum;  the  Grape;  the  Small  Fruits — Pre- 
ventive and  Remedial  Treatments — Deep  Planting  and  Mulching;  Use  of 
Hardy  Stocks;  Pruning;  Handling  Nursery  Stock  .in  Cold  Weather — 
Summary. 

CHAPTER  XVIII 

Winter  Injury  IN  Relation  TO  Specific  Fruits 318 

The  Apple — Injuries  A.ssociated  with  Immaturity;  Control  Measures; 
Varietal  Differences — The  Pear;  the  Peach;  the  Cherry;    tTie    Plum;    the 


xiv  CONTENTS 

Page 
Endosperm — The  Setting  of  the  Fruit — What  Constitutes  a  Normal  Set  of 
Fruit — The  June  Drop  and  Other  Drops — The  First  Drop;  the  Second  Drop; 
the  Third    Drop  or   June  Drop — Fruit  Setting,  Fruitfulness  and  Fertility 
Distinguished — Sterility  and  Unfruitfulness  Classified — Summary. 

CHAPTER  XXVII 

Unfruitfulness  Associated  with  Internal  Factors 489 

Due  Principally  to  Evolutionary  Tendencies — Imperfect  Flowers,  Dioecious 
and  Monoecious  Plants;  Heterostyly;  Dichogamy,  Protandry  and 
Protogyny;  Impotence  from  Degenerating  or  Absorbed  Pistils  or  Ovules; 
Impotence  of  Pollen — Due  Principally  to  Genetic  Influences — Sterility  and 
Unfruitfulness  Due  to  Hybridity — Incompatibility — Interfruitfulness  and 
Interfertihty;  in  Reciprocal  Crossings — Due  Principally  to  Physiological 
Influences — Unfruitfulness  Due  to  Slow  Growth  of  the  Pollen  Tube — Prema- 
ture or  Delayed  Pollination — Nutritive  Conditions  Within  the  Plant — Effect 
on  Pollen  Viability;  Effect  on  Defectiveness  of  Pistils;  Fruit  Setting  of 
Flowers  in  Different  Positions;  Strong  and  Weak  Spurs;  Evidence  from 
Ringing  Experiments;  Evidence  from  Starvation  Experiments — Summary. 


CHAPTER  XXVIII 

Unfruitfulness  Associated  with  External  Factors 509 

Nutrient  Supply;  Pruning  and  Grafting;  Locahty — Season — End-season 
FertiUty;  Change  of  Sex  with  Season — Age  and  Vigor  of  Plant;  Tempera- 
ture; Light;  Disturbed  Water  Relations;  Rain  at  Blossoming;  Wind;  Fungous 
and  Bacterial  Diseases;  Spraying  Trees  When  in  Bloom;  Other  Factors  That 
Cause  the  Dropping  of  Fruit  and  Flowers — Summary. 


CHAPTER  XXIX 

Factors  more  Directly  Concerned  in  the  Development  of  the  Fruit  .  .  521 
Stimulating  Effects  of  Pollen  on  Ovarian  and  Other  Tissues;  the  Effect  of 
Certain  Stimulating  Agents  on  Fruit  Setting — Seedlessness  and  Partheno- 
carpy — Seedlessness  of  Non-parthenocarpic  Fruits;  Vegetative  and  Stimula- 
tive Parthenocarpy;  Relation  of  Anatomical  Structure  of  Fruit  to 
Parthenocarpy;  the  Value  of  Seedless  and  Parthenocarpic  Fruits — The  Rela- 
tion of  Seed  Formation  to  Fruit  Development — Structure  of  Fruit;  Form; 
Size;  Composition  and  Quality;  Season  of  Maturity;  Specific  Influence  of 
Pollen  on  Resulting  Fruit — Summary. 


CHAPTER  XXX 

Fruit  Setting  as  an  Orchard  Problem 538 

The  Number  of  Pollenizers;  Temporary  Expedients;  PoUinating  Agents — 
The  Fruit  Setting  Habits  of  Different  Fruits— Apple;  Pear;  Quince;  Peach; 
Almond;  Plum;  Apricot;  Cherry;  Grape;  Strawberry;  Currant  and  Goose- 
berry; the  Brambles;  the  Nuts;  Persimmon — Summary. 


CONTENTS  XV 

SECTION  VI 
Propagation 

CHAPTER  XXXI 

Paqb 

The  Reciprocal  Influences  of  Stock  and  Cion 552 

The  Congeniality  of  Grafts — Congeniality  and  Adaptability  Distinguished — 
The  Influence  of  Stock  on  Cion — Stature;  P^orm — Seasonal  Changes — End- 
season  Effects,  Ripening  of  Fruit;  Maturity  of  Wood;  Spring  Effects — Hardi- 
ness— Disease  Resistance — Physiological  Diseases — Yield — Fruit-bud  Form- 
ation; Fruit  Setting;  Size  of  Fruit — Quality — In  Pomaceous  Fruits;  In 
Stone  Fruits;  in  Grapes;  Qualitative  Differences  and  Quantitative  Varia- 
tions— Longevity;  General  Influence  of  Stock  on  Cion — Influence  of  Cion 
on  Stock — Size  and  Number  of  Roots;  Distribution  and  Character  of  Roots; 
Longevity,   Growing  Season  and  Hardiness;  Other  Influences;  in  General. 


CHAPTER  XXXII 

The  Root  Systems  of  Fruit  Plants 584 

Conflicting  Interests  of  Nurseryman  and  Fruit  Grower — Adaptation  of  Stocks 
to  Particular  Conditions — Adaptation  to  Soil  Temperatures;  Adaptation  to 
Soil  Texture  and  Composition;  Immunity  or  Resistance  to  Soil  Parasites — 
Propagation  by  Cuttings — Advantages  and  Disadvantages — Grapes  in 
Particular;  Apples  and  Pears — Propagating  Apples  and  Pears  by  Layerage 
and  Hardwood  Cuttings — Varietal  Differences  and  Contributing  Factors — 
Sources  of  Nursery  Stock — Grades  of  Nursery  Stock — Selection  of  Seedling 
Stocks;  Grafted  or  Budded  Trees;  Double  Worked  Trees — Pedigreed  Trees — 
Some  Results  in  Citrus  Fruits;  Some  Results  in  Apples;  in  GeneraL 


SECTION  vn 

Geographic  Influences  in  Fruit  Production 
CHAPTER  XXXIII 

The  Geography  of  Fruit  Growing 612 

Life  Zones,  Crop  Zones  and  Fruit  Zones — The  Boreal  Zone;  the  Tropical 
Zone — Austral  or  Temperate  Zone — Transition  Zone;  Upper  Austral  Zone; 
Lower  Austral  or  Sub-tropic  Zone — Geography  of  Fruit  Production  as  Influ- 
enced by  Temperature — Peach  Growing  as  Influenced  by  Temperature; 
Grape  Growing  as  Influenced  by  Temperature;  Temperature  and  the 
Geographic  Range  of  Apple  Varieties;  the  Effect  of  Bodies  of  Water  on 
Temperature;  Influence  of  Altitude  on  Air  and  Soil  Temperatures — 
Geography  of  Fruit  Production  as  Influenced  by  Rainfall  and  Humidity — 
Other  Factors  Influencing  the  Geographic  Distribution  of  Fruits — Sunshine; 
Parasites;  Wind;  Native  Range  of  Parent  Species;  Length  of  Time  in  Culti- 
vation; Uses  and  Quality  of  Product;  Relation  to  Consuming  Centers  and 
Transportation  Facilities— Summary. 


XVI  CONTENTS 

CHAPTER  XXXIV 

Orchard  Locations  AND  Sites go- 

Orcharding  in  or  outside  of  an  Established  Fruit  Growing  Section;  Land 
Values;  Transportation  Facilities— Slope  or  Aspect— Influence  on  Soil  Tem- 
peratures and  on  the  Plant;  Specific  Influence  on  Fruit  Growing;  Indirect 
Effects;  Abruptness  of  Slope— Air  Drainage— Influence  of  Elevation— Ther^ 
mal  Belts— Influence  of  Bodies  of  Water— Influence  of  Distance  from  Water; 
Influence  of  Size  and  Shape  of  Body  of  Water;  Indirect  Temperature  Effects- 
Minor  Temperature  Effects— Importance  During  the  Winter;  Obstructions- 
Local  Variations  and  their  Significance— Temperature;  Evaporation,  Rainfall 
and  Other  Factors — Summary. 

CHAPTER  XXXV 

Orchard  Soils „_„ 

Considered  from  the  Standpoint  of  Physical  Condition— Requirements  of 
Different  Crops;  Requirements  as  to  Depth;  Classification  of  Soils  according 
to  Size  of  Soil  Particles;  Mechanical  Analyses  of  Various  Fruit  Soils- 
Considered  from  the  Standpoint  of  Chemical  Composition— Requirements 
of  Different  Crops— Chemical  Analyses  of  Various  Fruit  Soils— Evi- 
dence on  Soil  Requirements  from  Fertilizer  Experiments— Vegetation 
as  an  Index  to  Crop  Adaptation— Adaptation  of  Varieties  to  Particular 
Soils — Summary. 

Glossary   ....  „„. 
674 

'"""" 679 


THE  FUNDAMENTALS  OF 
FRUrr  PRODUCTION 

SECTION  I 
WATER  RELATIONS 

The  importance  of  moisture  as  a  factor  in  the  production  of  fruit 
is  appreciated  only  in  part.  In  arid  sections  the  lack  is  obvious;  in 
many  regions  certain  lands  are  recognized  as  too  moist  for  fruit  plants. 
In  the  majority  of  the  so-called  humid  sections,  however,  there  is  a 
tacit  assumption  that  nature  provides  satisfactorily  for  the  requirements 
of  fruit  plants.  Drought  may  diminish  or  destroy  other  crops,  but  as 
long  as  trees  survive  there  is  considered  to  be  sufficient  moisture. 

The  forest  trees,  relied  on  as  evidence  of  this  sufficiency,  show,  even 
in  a  limited  area,  striking  differences  in  vigor^  according  to  their  locations. 
One  of  the  most  important  factors  recognized  by  the  forester  as  affecting 
tree  growth,  is  moisture.  Certain  spots  even  in  humid  regions,  are 
chronically  dry,  some  are  nearly  always  wet;  others,  favorable  in  some 
seasons,  are  subject  rather  frequently  to  excess  or  deficiency  of  moisture. 

Much  of  the  complacence  concerning  the  water  supply  of  trees  is 
based  on  the  supposedly  great  range  of  their  roots  and  the  consequent 
great  amount  of  soil  from  which  they  can  draw  water#  For  this  reason 
a  statement  of  the  extent  to  which  forest  trees  actually  deplete  the  soil 
moisture  is  pertinent.  Zon^^^  cites  data  showing  moisture  contents 
in  June  of  4.5  and  4.8  per  cent,  respectively  at  4  and  8  inches  in  soil 
through  which  forest  tree  roots  were  ranging,  while  adjacent  spots  within 
the  forest,  exactly  similar  except  that  the  roots  had  been  excluded  con- 
tained, at  the  san>e  depths,  13.8  and  11.0  per  cent,  respectively.  At' 
16  inches  the  root  free  soil  had  over  twice  as  much  moisture  as  that  to 
which  the  roots  had  access.  Evidence  is  cited  to  the  effect  that  the 
water  level  is  lowered  under  forest  and  that  with  the  removal  of  the  forest 
the  water  level  rises.  Zon  considers  that  the  inability  of  many  species 
to  grow  under  an  established  cover  of  trees,  commonly  called  shade 
intolerance,  is  in  reahty  due  to  the  low  supply  of  moisture  in  the  soil. 
When  the  roots  of  the  top  growth  are  excluded  from  an  area,  the  intol- 
erant species  grow  there  with  considerable  vigor. 

Deficient  and  excessive  moisture  are  admittedly  each  a  hmiting 
factor  in  crop  production.     Table  1,  based  on  estimates  by  crop  reporters 

1 


2  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

of  the  United  States  Department  of  Agriculture,  shows  the  damage 
caused  by  injurious  moisture  conditions  in  comparison  with  other  factors. 
The  figures  on  apples  and  berries  are  averages  for  the  period  1912-1919 
and  on  other  crops  selected  in  comparison  for  the  period  1909-1919. 
According  to  these  estimates  small  fruits  suffer  more  from  drought  than 
from  any  other  single  factor,  while  apples  are  injured  more  only  by  cold 
weather. 


Table  1 

— Damage  to 

Crops  from  D 

IFFERENT 

Causes 

(After  Smith^' 

V) 

1 

1 

■^ 

i 

1 

*i 

1 

1 

S 

I 

a 

1     . 

1    . 

i 

t 

a 
g 
>- 

4 

i 

1 

1 

i 

1 

a 

Is 

>   c 

1 " 

^  s 

t 

s 

i 

& 

•a 

"S  «■ 

> 

a 

p 

1^ 

E 

P 

■3 

1 

2 

1^ 

|§ 

a   a 

ii 

1 

Wheat        

12.4 
16.3 

2.0 
4.0 

0.3 
0.9 

4.5 
2.9 

1. 1 
0.4 

2.0 

2.2 

0.3 
0.5 

22.9 

27.7 

2.7 
0.2 

2.1 
2.7 

0.2 
0.2 

0.2 
0.7 

28  8 

Corn 

31.1 

6.7 
14.4 

3.1 
3.1 

1.5 
0.2 

0.3 

1.6 

0.1 

0.4 
0.7 

1.8 
0.1 

14.1 
20.7 

1.2 

4.4 

0.8 
3.2 

0.3 
0.1 

0.1 
0.3 

Potatoes 

30.0 

Tobacco 

8.7 

3.7 

0.6 

1.  1 

0.8 

0.2 

0.3 

15.8 

0.4 

2.6 

0.1 

20.5 

Cotton 

12.3 

4.3 

1.0 

1.4 

0.5 

1.6 

0.7 

22.3 

2.0 

9.7 

0.2 

35.5 

Apples 

5.4 

1.6 

0.2 

14.6 

0.8 

0.5 

0.9 

24.9 

3.7 

3.6 

0.1 

39.6 

Berries 

9.3 

1.7 

0.2 

7.3 

0.5 

0.6 

0.2 

20.3 

1.1 

0.6 

0.1 

24.9 

Precipitation  cannot  be  controlled.  Soil  moisture,  however,  is  sus- 
ceptible more  or  less  to  modification  by  various  practices  and  adjust- 
ments of  fruits  or  of  stocks  for  fruits  can  be  made  in  some  cases  to  the 
moisture  conditions  of  the  soil.  For  these  reasons  recognition  of  soil 
conditions,  understanding  of  the  water  requirements  of  the  various  fruit 
plants  and  knowledge  of  the  relation  of  various  cultural  practices  to 
moisture  control  are  of  fundamental  importance  to  the  fruit  grower. 


CHAPTER  I 

THE  WATER  REQUIREMENTS  OF  FRUIT  PLANTS 

There  is  more  or  less  acknowledgement  of  a  difference  in  adaptability 
of  different  fruits  to  varying  moisture  conditions  in  the  soil;  this  is, 
however,  expressed  in  terms  of  tolerance  more  often  than  in  terms  of 
requirements.  It  is  stated  frequently  that  sour  cherries  will  stand  a 
dry  soil  or  that  pears  will  endure  a  wet  soil;  there  is  very  little  exact 
information  on  what  the  various  fruits  actually  require.  Table  2  gives 
some  interesting  results  of  investigation  in  California  on  the  requirements 
of  fruit  and  other  crops  under  conditions  common  in  that  section.  The 
requirements  of  the  several  fruits  stated  in  terms  of  the  amounts  of  free 
water  in  the  soil,  exhibit  a  considerable  difference.  Other  data  to  be 
introduced  later  (Tables  11  and  12)  show  that  the  same  fruit  may  have 
different  moisture  requirements  in  different  localities. 


Table  2.- 


-Relative  Water  Requirements  of  Different  Plants 

(After  Loughridge^'') 


Free  water  in 

4  feet  of  soil 

Plants  for  which  the  soil 

Plants  for  which  the  soil 

moisture  is  just  above  the 

moisture  is  just  below  the 

Percent- 

Tons per 

minimum;  cultures  did  well 

minimum;  cultures  suffered 

age 

acre 

0.0  to  1.0 

80 

Apricots,  olives,  peaches,  soy 
bean 

Citrus,  pears,    plums,  acacia 

1.0  to  1.5 

120 

Citrus,  figs 

Almonds,  apples 

1.5  to2.0 

160 

Almonds,  plums,  saltbush 

Barley 

2.0  to2.5 

200 

Walnuts,  grapes,  eucalyptus 

2.5  to3.0 

240 

Apples,  prunes 

Prunes 

3.0  to4.0 

322 

Pears,  hairy  vetch 

Wheat 

4.0  to  5 . 0 

400 

Wheat,  corn 

5.0  to.6.0 

480 

Sugar  beets,  sorghum 

Sugar  beets 

/  Water  as  a  Plant  Constituent. — Water  is  a  normal  constituent  of  all 
plant  tissues,  comprising  from  50  to  75  per  cent,  of  the  leaves  and  twigs, 
from  60  to  85  per  cent,  of  the  roots,  and  85  per  cent,  or  more  of  most 
fleshy  fruits. 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Table  3.— Typical  Water  Content 

3F  Fruit  Plants  in  the    Fall'29 

Fruit 

Flesh 

Skin 

Core 

or 
stone 

Stem 

Leaves 

New 
growth 

Old 
growth 

85.64 
86.78 

89.74 
86.07 
88.78 
88.06 
89.98 

85.81 
78.32 

85.71 
83.62 
32.67 
32.83 
46.81 

59.52 
68.76 

75.18 

53.00 
38.20 
63.78 
61.10 
65.10 
65.97 
48.14 
66.25 
33.28 
69.00 

49.40 
50.33 
49.52 
49.59 
49.51 
50.36 
38.15 
44.20 
41.33 
54.33 

Pear       

Peach 

Plum 

Cherry                     

Currant                   .... 

87.13 
85.10 
89.42 
84.35 
78.44 

45.74 

Blackberry        

38.26 

39.77 

33.52 

Table  4  indicates  the  amounts  of  water  found  in  various  parts  of  the 
chestnut  and  walnut  at  different  seasons  and  Table  5  shows  the  mois- 
ture content  of  bearing,  non-bearing  and  barren  spurs  of  the  apple  at 
various  periods.  All  spurs  have  a  maximum  water  content  during  or 
directly  after  the  time  of  blossoming,  but  blossoming  spurs  contain 
much  more  water  than  spurs  in  the  off  year  and  these  more  than 
barren  spurs. 


Table  4. — Typical  Water  Content  of  Roots,   Branches  and  Leaves  of  the 
Chestnut  and  Walnut^ 


Chestnut 

May  30 

July  4 

Aug.  11 

Sept.  25 

Roots. . . . 
Branches . 
Leaves .  .  . 





83.31 
78.68 
76.51 

66.12 
69.49 
71.44 

64.23 
51.69 

68.82 

59.82 
53.32 
57.85 

Walnut 

July  31 

Sept.  15 

Nov.  6 

Roots 

Branches 

Leaves 

75.21 
68.30 
59.54   • 

69.54 
58.53 
52.00 

73.19 
68.43 

64.87 

Besides  being  a  plant  constituent,  water  is  a  plant  nutrient  and  as  such 
is  indispensible  for  the  manufacture  of  plant  material,  particularly  in  the 
photosynthetic  production  of  carbohydrates.  Finally,  water  is  the 
medium  in  which  all  the  nutrients  essential  to  green  plants,  except  carbon, 
occur  in  solution.  > 


THE  WATER  REQUIREMENTS  OF  FRUIT  PLANTS 
Table  5. — Variations  in  the  Water  Content  of  Apple  Sptjrs^^ 


Feb. 

Mar. 

Mar. 

May 

June 

Sept. 

Nov. 

Jan. 

4 

11 

26 

13 

26 

2 

19 

24 

Bearing  Spurs: 

Wealthy 

49.9 

65.5 

61.1 

53.2 

50.5 

45.7 

Ben  Davis 

60.0 

64.6 

61.8 

55.2 

51.6 

51.1 

Jonathan 

47.5 

63.2 

60.2 

54.8 

51.6 

47.7 

Non-bearing  Spurs: 

Jonathan 

47.1 

54.8 

53.0 

51.4 

48.6 

49.6 

Ben  Davis 

50.8 

59.8 

55.1 

48.6 

48.5 

48.9 

Barren  Spurs: 

Ben  Davis 

45.6 

52.7 

47.8 

47.6 

44.6 

45.5 

Nixonite 

47.4 

.... 

56.2 

51.4 

47.6 

48.6 

43.1 

'^  The  Water  Requirements  of  Plants  in  Terms  of  Dry  Weight. — The 

water  requirement  of  any  plant  is  defined  as  the  amount  of  water  used 
while  a  unit  weight  of  dry  matter  is  produced.  The  weights  may  be 
measured  in  grams  or  in  pounds,  but  the  ratio  obtained  is  the  same  in 
any  easel  Table  6  brings  together  data  that  have  a  bearing  on  this 
point,  as  reported  by  several  investigators. 


Table 


-Water  Evaporated  by  Growing  Plants  for  1  Part  of  Dry  Matter 
Produced*' 


Lawes  and  Gilbert 
(England) 


Hellriegel 
(Germany) 


Wollny 
(Germany) 


King 
(Wisconsin) 


Peas 235 

Barley 262 

Red  clover 249 

Beans 214 

Wheat 225 


Peas 292 

Barley 310 

Red  clover...  330 

Beans 262 

Wheat 354 

Oats 402 

Buckwheat. ...  374 

Lupin 373 

Rye 377 


Peas 479 

Barley 774 

Maize 233 

Millet 416 

Oats 665 

Buckwheat. . . .  664 

Rape 912 

Sunflower 490 

Mustard 843 


Peas 447 

Barley 393 

Red  clover.  .  .  .  453 

Maize 272 

Potatoes 423 

Oats 557 


Though  Table  6  does  not  include  figures  for  fruit  plants  it  is  presumed 
that  as  a  class  they  do  not  differ  materially  from  herbaceous  plants  in 
this  respect.  yHilgard"^  states  that  oaks  require  from  200  to  300  pounds 
of  water  for  each  pound  of  dry  matter  produced,  while  birches  and  lindens 
use  from  600  to  700  pounds  in  producing  1  pound  of  dry  leaves;  the 
figures  for  beech  and  maple  are  intermediate.     Hilgard  estimates  from 


6  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

30  to  70  units  of  water  needed  for  the  production  of  one  unit  of  dry  matter 
in  spruce,  fir  and  pine  trees.  Thus  the  range  in  water  requirement  for  at 
least  some  of  the  ordinary  deciduous  trees  is  similar  to  that  of  herbaceous 
crops  grown  under  similar  conditions. 

Two  striking  points  are  shown  by  these  figures  on  water  requirements : 
(1)  the  great  differences  in  the  water  requirements  of  different  species 
and  (2)  the  variation  shown  by  the  same  plant  in  different  sections, 
according  to  the  determinations  of  different  investigators. 

These  differences  carry  two  suggestions  of  practical  import  in  fruit 
production;  first,  that  certain  species  or  certain  fruits  can  do  more  than 
others  with  a  given  amount  of  water,  second,  that  the  same  species  of 
fruit  plant  will  produce  more  vegetative  growth  with  a  given  supply  of 
water  under  certain  conditions  than  under  others. 

The  Water  Requirements  of  Plants  in  Terms  of  Precipitation. — 
Figures  have  been  given  showing  the  approximate  water  requirements 
of  plants  in  terms  of  the  number  of  units  of  water  used  while  one  unit  of 
dry  matter  is  produced.  It  is  interesting  to  speculate  as  to  what  these 
figures  mean  in  terms  of  rainfall  or  amounts  of  irrigation  water. 

Amounts  Used  by  the  Plants  Themselves. — Thompson ^^^  has  calcu- 
lated the  average  weight  of  wood,  roots  and  leaves  produced  by  a  normal 
healthy  peach  tree  up  to  the  time  it  has  attained  the  age  of  9  years  as 
approximately  215  pounds.  This  represents  an  average  annual  dry 
weight  production  of  wood,  leaves  and  roots  of  approximately  ^5  pounds. 
With  increasing  age  the  amount  would  be  somewhat  greater.  If  a  300 
bushel  per  acre  yield  is  assumed,  it  means  the  production  of  approximately 
20  pounds  of  dry  matter  per  tree  to  be  taken  away  in  the  form  of  fruit. 
In  other  words,  the  mature  peach  tree  would  be  expected  to  produce 
about  45  pounds  of  dry  matter  per  year.  Assuming  a  stand  of  100  trees 
to  the  acre  this  would  mean  a  production  of  4,500  pounds  of  dry  matter 
per  acre.  If  it  takes  500  parts  of  water  to  produce  one  part  of  dry 
weight,  it  would  require  22,500  pounds,  over  11  tons  or  nearly  3,000  gallons 
per  tree  to  mature  the  crop  properly.  This  estimate  considers  only  the 
amount  actually  taken  up  by  the  roots  and  for  the  most  part  transpired 
through  the  leaves  and  does  not  make  any  allowance  for  run-off  from  the 
surface,  or  for  seepage  and  evaporation.'  It  means  300,000  gallons  per 
acre  equivalent  to  a  rainfall  of  approximately  11  inches,  or  an  equivalent 
amount  of  irrigation  water.  For  each  additional  100  bushels  of  fruit 
per  acre  approximately  2  acre-inches  more  would  be  required  b}^  the 
plant.  Looking  at  the  matter  from  another  angle,  for  every  acre- 
inch  under  the  11  that  is  denied  the  trees,  there  would  be  a  decrease  in 
yield  of  approximately  50  bushels.  Of  course,  if  the  water  requirement  of 
this  fruit  is  only  300  instead  of  500  under  a  given  set  of  conditions,  7  acre- 
inches  actually  available  to  the  trees  would  mature  as  large  a  crop  as 
the  11  acre-inches  in  the  first  instance. 


THE  WATER  REQUIREMENTS  OF  FRUIT  PLANTS  7 

That  the  first  presented  figures  are  probably  representative  for  many 
tree  fruits  is  suggested  by  their  close  agreement  with  the  9  acre-inches 
estimate  of  Hilgard^^  as  the  water  requirement  of  15-year  old  orange 
trees  in  southern  California  and  the  4,500  gallons  per  tree  estimate  of 
Duggar43  as  the  requirement  of  a  30-year  old  apple  tree.  It  is  interesting 
to  note  that  a  12-inch  summer  rainfall  has  been  estimated  as  sufficient  for 
the  actual  water  consumption  of  100-year  old  beech  trees  standing  about 
200  to  the  acre.^^  Data  presented  in  Table  6  show  that  the  variation  in 
the  water  requirements  of  individual  crops  often  exceeds  the  difference 
of  200  assumed  in  the  case  of  the  peach  orchard.  This  emphasizes  the 
point  that  it  is  frequently  a  matter  of  much  practical  importance  to 
provide  the  tree  with  as  nearly  optimum  nutritive  conditions  as  possible, 
to  secure  the  economical  use  of  water  if  for  no  other  reason. 

Total  Amounts  Required  for  Plants  and  to  Compensate  for  Evaporation 
Run-off  and  Seepage. — It  should  be  noted  that  in  the  last  paragraph  when 
7  to  11  acre-inches  of  water  was  mentioned,  as  approximately  the  amount 
required  to  mature  a  peach  crop  of  a  certain  size,  reference  was  made 
only  to  the  water  actually  taken  up  and  used  by  the  plant.  As  is  well 
known,  a  considerable  percentage  of  the  water  that  reaches  the  land  as 
rain  or  snow  or  through  the  irrigation  channel  is  made  unavailable  by 
run-off,  evaporation  and  seepage.  The  exact  percentages  removed  in 
these  ways  vary  greatly,  depending  on  the  seasonal  distribution  of  the 
rainfall,  the  topography,  the  character  of  soil  and  subsoil,  the  atmos- 
pheric humidity  and  other  factors.  It  has  been  estimated  that  in  the 
forest,  where  conditions  are  more  favorable  than  in  most  fruit  plantations 
for  the  reduction  of  run-off  and  evaporation,  probably  not  more  than  35 
per  cent,  of  the  precipitation  actually  becomes  available  for  tree  growth. '^ 
In  orchard  practice  then,  it  is  doubtful  if  much  more  than  one-third  of 
the  natural  precipitation  or  irrigation  water  can  be  considered  to  be 
utihzed  by  the  trees,  and  under  poor  methods  of  soil  management  or  in 
soils  of  poor  water-absorbing  and  water  holding  capacity  the  percentage 
may  be  much  lower. 

In  the  light  of  what  has  been  said  it  obviously  would  be  impracticable 
to  attempt  the  construction  of  a  table  showing  the  rainfall  requirements  of 
different  fruit  crops,  such  as  strawberries,  cherries,  apples  and  olives,  for 
there  are  too  many  contributing  factors  to  be  evaluated,  but  the  general 
principles  that  have  been  given  should  be  capable  of  interpretation  and 
intelligent  application  to  many  concrete  practical  problems  as  they  arise 
in  orchard  management.  For  instance,  with  a  fairly  accurate  knowledge 
of  the  mean  and  minimum  rainfall  of  a  particular  location  and  its  seasonal 
distribution,  and  after  a  first  hand  study  of  soil  conditions  as  they  relate 
to  moisture,  it  should  not  be  difficult  to  determine  more  or  less  accurately 
the  practicability  of  growing  a  certain  fruit  crop  without  irrigation 
facilities,  or  to  determine  the  relative  importance  of  certain  moisture 


8  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

conserving  practices.  Experience  may  be  a  still  better  guide  but  only 
to  the  extent  that  it  gives  ability  to  judge  local  conditions  and  so  permits 
a  more  accurate  interpretation  and  application  of  general  principles. 

Some  measure  of  the  way  these  principles  apply  to  concrete  cases 
may  be  obtained  from  the  statement  that  it  has  been  found  practicable 
to  use  irrigation  water  amounting  to  about  30  acre-inches  for  mature 
peach  trees  on  some  of  the  gravelly  loams  of  Utah  and  40  acre-inches  on 
full  bearing  apple  orchards  on  sandy  loam  in  Idaho  where  rainfall  aver- 
aged 10  or  less  inches  per  year.  On  the  other  hand,  heavy  crops  of  sweet 
cherries,  prunes  and  apricots  are  obtained  without  irrigation  from 
orchards  on  a  light  sandy  loam  at  The  Dalles,  Ore.,  with  an  average 
annual  rainfall  of  16  or  17  inches. 

Some  years  ago  16  or  18  inches  of  rainfall  annually  was  generally 
considered  sufficient  for  the  production  of  deciduous  fruits  in  California, 
but  experience  has  demonstrated  that  the  percentage  of  this  amount 
that  is  actually  left  for  the  trees  after  run-off,  seepage  and  evaporation 
is  not  adequate  for  the  average  orchard  with  the  trees  spaced  the  usual 
distances.  As  a  matter  of  fact  there  is  a  growing  belief  that  even  a 
rainfall  of  30  inches  in  California  should  be  supplemented  by  provision 
for  irrigation  to  take  care  of  occasional  emergencies. i" 

Planting  Distances  Related  to  Moisture  Supply. — Application  of  the 
principles  just  pointed  out  to  particular  fruits  and  particular  locations 
should  be  the  main  deciding  factor  in  determining  distance  of  planting  for 
orchard  fruits,  for  water  supply  is  most  frequently  the  liqiiting  factor  in 
this  connection  even  though  the  grower  seldom  realizes  it  at  the  time  of 
setting.  This  is  contrary,  in  the  way  it  often  works  out,  to  the  frequently 
repeated  statement  that  trees  can  be  planted  more  closely  in  a  "poor" 
than  in  a  "good"  soil.  If  the  soil  is  "poor"  because  it  is  shallow  or  of 
poor  water-holding  capacity  unproductiveness  will  only  be  increased  by 
closer  spacing.  In  soils  that  are  both  fertile  and  well-watered,  planting 
distance  should  be  governed  by  the  size  of  the  plants  and  the  growing 
habit.  If  they  are  infertile  and  well-watered,  again  planting  distance 
should  be  determined  by  size  of  plant  and  growing  habit,  and  the  fertility 
question  solved  through  the  proper  use  of  fertilizers.  If  moisture  is  the 
limiting  factor,  regardless  of  the  relative  productivity  of  the  land,  spacing 
should  be  determined  largely  by  moisture  requirements,  though  due 
attention  should  be  given  to  growth  characteristics. 

A  notable  instance  of  the  intelligent  and  successful  application  of  these 
principles  to  the  question  of  planting  distance  is  found  in  some  of  the  olive 
orchards  of  northern  Africa.  Though  the  usual  planting  distance  for  this  fruit 
in  irrigated  sections,  or  in  regions  of  ample  rainfall  is  18  to  22  feet,  near  Sfax  in 
Tunis  the  trees  are  planted  60  to  80  feet  apart,  making  only  7  or  8  to  the 
acre.  This  arrangement  makes  possible  a  profitable  dry-land  industry  without 
irrigation,  though  the  mean  annual  rainfall  is  only  9.3  inches  and  though  there 


THE  WATER  REQUIREMENTS  OF  FRUIT  PLANTS  9 

\ 

are  often  several  successive  years  in  which  the  total  precipitation  does  not 
exceed  6  inches."^ 

Another  interesting  application  of  the  same  principle  has  been  recorded  in 
South  Dakota.  Cottonwoods  planted  rather  close  together  for  windbreak  or 
shelter  belt  purposes,  thrive  for  a  number  of  years,  but  eventually  a  stage  is. 
reached  when  they  begin  to  die  from  crowding.  If  wider  spacing  or  thinning  is 
practiced  their  longevity  is  increased  correspondingly.^* 

Factors  Influencing  the  Water  Requirements  of  Plants. — It  is  advisable 
at  this  point  to  review  some  of  the  data  available  on  the  economy  with 
which  the  plant  uses  water.  From  what  has  been  said  regarding  the  total 
water  requirements  of  the  plant  it  is  evident  that  only  an  extremely 
small  percentage  is  finally  held  by  the  plant  as  a  constituent  of  the  proto- 
plasm or  is  used  in  the  manufacture  of  chemical  compounds.  The 
greater  portion  of  the  water  has  been  required  to  meet  evaporation. 
Since  the  water  requirement  is  a  ratio  between  the  water  used  and  the 
plant  material  produced,  it  is  evident  that  all  other  factors  favoring  the 
nutrition  of  land  plants  will  tend  to  decrease  their  water  requirement  and 
that  all  factors  tending  to  increase  water  loss  through  transpiration 
will  increase  it.  Experimental  evidence  bearing  on  the  factors  affect- 
ing, nutrition  is  available,  but  the  effects  of  factors  altering  water  loss 
have  not  been  so  thoroughly  studied. 

Nutrient  Supply. — Table  7  show^s  the  mean  water  requirements  of 
oats  and  wheat  as  influenced  by  fertilizer  treatments  and  Table  8  presents 
data  showing  the  effects  of  various  amounts  of  nitrogen  upon  the  water 
requirement  of  the  plant. 

It  is  a  reasonable  assumption  that  when  the  soil  solution  is  poor  in 
any  indispensible  element  more  water  must  be  taken  up  by  the  plant  to 
obtain  an  ample  amount  of  this  element.  However,  this  is  true  only 
within  certain  limits,  because  of  the  abiUty  of  plants  to  withdraw  from 
the  soil  nutrient  materials  in  proportions  quite  different  from  thofee  in 
which  they  occur  there.  Attention  has  been  called  to  the  considerably 
higher  water  requirement  of  plants  in  the  very  rainy  climate  of  Munich, 
Germany,  than  in  the  drier  portions  of  northern  Germany  or  in  Wis- 
consin. It  is  suggested  that  as  the  moisture  approaches  the  extreme  in  a 
wet  soil  the  soil  solution  is  diluted;  hence  conditions  are  presented  that  at 
least  in  a  way  are  comparable  with  those  found  in  a  "poor"  soil.  More 
water  is  required  to  absorb  a  given  amount  of  nutrients.  Possibly  in  this 
case  the  poor  aeration  attendant  upon  a  soil  moisture  content  above  the 
optimum  may  also  affect  the  water  requirement.  The  effects  of  a  very 
dry  soil,  which  Hkewise  increases  the  water  requirement,  is  attributed  by 
Briggs  and  Shantz^^  to  the  restricted  area  which  the  active  roots  and  root 
hairs  occupy  under  these  conditions.  It  seems  a  strange  perversity  of 
fate  that  the  soil  conditions  and  soil  treatment  which  are  most  likely  to 
result  in  a  restricted  root  system,  such  as  heavy  soils,  hardpan,  water- 


10 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


logging,  puddling  and  baking,  are  those  which  lead  to  an  increased  water 
requirement  of  the  plant. 

Table  7. — Mean  Water  Requirements  of  Oats  and  Wheat  with  Different 

Fertilizer  Treatments 

{From  determinations  made  by  Liebacher,  Von  Seelhorst,  Bunrjer  and  Ohlmer^^) 

Mean  Water  Require- 
ments FOR  Oats 
AND  Wheat 


Fertilizer 

KN  P.. 
N  P.. 
NK.. 

N.. 

P  K.. 

P.. 

Check.. 

K.. 


238 
243 
246 
259 
294 
297 
308 
314 


Table  8. — Effects  of  Various  Amounts  op  Nitrogen  on  the  Water  Require- 
ment OF  Plants 

{After  Hellriegel  ^2) 


CaNOa  supplied 
(grams) 

Dry  matter 

produced 

(grams) 

Water 

transpired 

(grams) 

Water 
requirement 

1.640 
1.312 
0.984 
0.656 
0.328 
0.000 

25.026 
23.026 
18.288 
13 . 936 
8.479 
1,103 

7451 
6957 
6317 
4839 
3386 
956 

292 
302 
345 
347 
399 
867 

Cultivation. — Bearing  directly  on  this  point  are  data  obtained  on  the 
effects  of  cultivation  in  lessening  the  water  requirements  of  plants.  Some 
of  these  data  are  presented  in  Table  9.     In  every  case  the  water  require- 


Table ' 


-The  Influence  of  Cultivation  Upon  Water  Requirements  of  Plants 
in  Different  Soils'"^ 


Not  cultivated 


Cultivated 


Sandy  loam .  .  ,  . 

Clay  loam 

Clay 

Type  not  given . 


603 
535 
753 

451 


252 
428 

582 
265 


ment  was  materially  reduced  by  cultivation;  in  one  case  it  was  more  than 
cut  in  two.  In  certain  soils  the  influence  of  cultivation  was  much  more 
pronounced  than  in  others.     Presumably  cultivation  affects  the  water 


THE  WATER  REQUIREMENTS  OF  FRUIT  PLANTS 


11 


requirements  of  plants  by  increasing  both  the  moisture  content  of  the  soil 
and  the  supply  of  available  plant  nutrients. 

Light. — It  should  not  be  inferred  from  what  has  been  said,  that  the 
plant's  water  requirement  is  entirely  governed  by  its  nutrition.  Investi- 
gation has  shown,  for  instance,  that  in  tobacco,  the  amount  of  water 
absorbed  is  quite  independent  of  the  amount  of  mineral  constituents 
taken  in.**  Thus  the  average  ratio  of  water  to  ash  for  six  plants  grown 
in  the  open  was  2,548,  while  for  six  plants  grown  under  shade  it  was  1,718. 
These  data,  however,  apply  only  to  the  water-ash  ratio  of  plants  growing 
in  full  sunlight  and  in  shade.  For  the  water-dry-matter  ratio  in  sunlight 
and  shade  a  somewhat  different  condition  holds,  probably  because  of  the 
influence  of  the  sunlight  in  promoting  photosynthetic  activities  and  the 
storage  of  elaborated  materials. 


Table  10. — Water  Requirements  per  Unit  of  Dry  Weight  of  Leaves  in  Sun  and 

Shade 

{After  HoneP^) 

(Kilograms  per  100  grams  of  dry  leaves) 


Species 


Sun 


Shade 


Beech \  76 .  18 

Hornbeam ;  81 .  30 

Sycamore 61 .  69 

Scots  pine 19. 15 

Silver  fir 13.91 

Black  pine 8 .  76 


107.80 

98.90 

76.19 

5.02 

4.85 
5.25 


Data  presented  in  Table  10  show  that  in  all  the  broad-leaved  trees 
studied,  the  water-dry-matter  ratio  rose  in  the  shade,  though  with  the 
conifers  it  was  greatly  lowered.  The  data  on  tobacco  alone  might 
suggest  that  with  the  nutrition  factor  constant  more  water  would  be 
required  in  exposed  than  in  protected  situations  and  that  shading  and 
windbreaks  might  be  expected  to  reduce  materially  the  plant's  water 
requirements.  On  the  other  hand,  the  data  of  Hasselbring  and  Honel 
together  lead  to  the  inference  that  though  the  mineral  requirements  of  the 
plant  as  related  to  water  suppl}^  may  be  increased  in  exposed  and  de- 
creased in  protected  situations,  tissue  building  and  the  manufacture 
and  storage  of  elaborated  materials  may  be  promoted  by  the  opposite 
conditions. 

In  General. — Recent  investigations  by  Briggs  and  Shantz^^  iead 
them  to  conclude  that  when  a  crop  is  thoroughly  adapted  to  a  certain 
environment  it  has  its  water  requirement  at  the  minimum  and  that  its 
water  requirement  gradually  increases  as  it  is  forced  to  grow  in  more 
and  more  uncongenial  conditions,  whatever  they  may  be.     Thus  as  a 


12  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

rule,  cool  weather  crops  have  a  lower  water  requirement  in  a  cool  than 
in  a  warm  climate,  the  reverse  being  true  of  warm  weather  crops.  In 
the  latter  instance,  however,  the  difference  is  less  pronounced,  due  to 
the  effect  of  increase  in  temperature  upon  transpiration  in  general. 

As  will  be  shown  later,  however,  plants  are  able  to  adapt  themselves 
in  certain  ways  to  dry  conditions,  the  result  being  a  lowering  of  what 
otherwise  would  be  a  very  high  transpiration  rate.  Only  limited  data 
are  available  as  to  how  these  tendencies  balance  each  other  and  as  to 
what  is  the  final  resultant.  Leather^^  has  found  that  at  Pusa,  India, 
the  water  requirements  of  wheat,  barley,  oats  and  peas  are  nearly  twice 
those  of  maize,  though  this  ratio  does  not  hold  in  most  sections  (see 
Table  6) .  Apparently  this  high  water  requirement  of  these  cool  season 
crops  is  associated  with  their  maturing  during  the  dry  season,  while 
in  India  maize  matures  during  the  more  humid  season  of  the  monsoon. 
The  greater  water  requirement  of  plants  cropped  by  means  of  pasturing 
as  compared  with  that  of  plants  which  are  allowed  to  continue  their 
growth  uncropped,^^''  may  be  taken  as  an  indication  that  new  growth 
has  a  higher  water  requirement  than  older  growth.  It  would  seem  that 
the  water  requirements  of  different  plants  vary  mainly  because  of  differ- 
ences in  the  economy  of  their  nutrition  and  })ecause  of  different  physio- 
logical and  structural  modifications  affecting  their  rate  of  transpiration. 

Some  Applications  to  Practice. — The  influence  of  both  the  chemical 
and  the  physical  conditions  of  the  soil  upon  the  water  requirement 
of  the  plant  is  of  practical  importance  to  the  grower,  the  influence  of 
soil  productivity  being  particularly  significant.  Few  realize  that,  when 
the  soil  provides  conditions  for  tree  growth  that  are  optimum  from  the 
standpoint  of  nutrient  supply,  actually  less  water  is  required  for  a  given 
yield  than  when  the  plant  is  handicapped  because  of  the  lack  of  some 
nutrient  as  well.  This  difference  in  water  requirement  is  not  one  of 
academic  interest  only;  it  is  large  enough  frequently  to  account  for  crop 
failure  or  crop  success  under  conditions  of  limited  water  supply. 

A  quotation  from  King^^  jg  to  the  point:  "In  the  long  series  of  studies  made 
by  the  writer  on  the  amounts  of  water  required  for  a  pound  of  dry  matter,  it  was 
found  true,  almost  without  exception,  that  strong  vigorous  growth  and  high 
yields  of  dry  matter  are  always  associated  with  a  small  transpiration  of  water 
when  measured  by  the  dry  matter  produced." 

Even  more  significant  is  the  statement  of  Leather,*''  who  made  a  careful 
study  of  this  question  in  the  dry  climate  of  Pusa,  India:  "The  effect  of  a  suitable 
manure  in  aiding  the  plant  to  economize  water  is  the  most  important  factor 
which  has  yet  been  noticed  in  relation  to  transpiration." 

It  would  probably  be  a  mistake  to  advise  watering  or  irrigating  trees 
by  fertilizing  them,  because  the  advice  would  be  taken  too  literally. 
Nevertheless,  the  reduction  of  the  water  requirement  of  the  plant  by 
maintaining  the  soil  in  a  condition  as  near  as  possible  to  the  optimum 


THE  WATER  REQUIREMENTS  OF  FRUIT  PLANTS  13 

with  respect  to  nutrient  supply  should  be  a  constant  and  conscious  aim 
in  scientific  orchard  management,  though  perhaps  the  water  conservation 
influence  of  optimum  growing  conditions  may  be  more  or  less  masked 
by  the  increased  requirements  for  the  accompanying  increased  growth. 

The  Wilting  Point  for  Fruit  Plants. — There  seems  to  be  some  differ- 
ence of  opinion  as  to  how  near  to  the  hygroscopic  coefficient  plants  can 
exhaust  the  water  supply  of  the  soil.  Loughridge  states  that  certain 
plants  can  remove  enough  of  the  hygroscopic  moisture  of  the  soil  to 
maintain  life  though  they  cannpt  grow  under  these  conditions;  Hilgard 
states  that  soils  of  great  hygroscopic  power  can  withdraw  from  moist 
air  enough  moisture  to  be  of  material  help  in  sustaining  the  life  of  vegeta- 
tion in  rainless  summers  or  in  time  of  drought,  though  only  a  few  desert 
plants  can  maintain  normal  growth.^*  In  most  plants,  however,  wilting 
will  occur  before  the  moisture  content  of  the  soil  has  been  reduced  to  its 
hygroscopic  coefficient. 

Wilting  Coefficients. — The  work  of  Briggs  and  Shantz^"  has  led  them 

to    conclude    that   the   wilting   coefficients  for  most   soils  equal  their 

hygroscopic  coefficient      _,,  ,     .  .,,       ,  .  ^ 

— ^po   I   n  nio Thus  a  sandy  loam  with  a  hygroscopic  coefli- 

cient  of  3.5  per  cent,  would  have  a  wilting  coefficient  of  about  4.8  and  a 
clay  loam  with  a  hygroscop/c  coefficient  of  11.4  would  have  a  wilting  coeffi- 
cient of  16.3  per  cent.  These  investigators  state,  "The  wilting  coeffi- 
cient is  the  same,  within  the  limits  of  experimental  error,  for  a  plant  in 
all  stages  of  development.  In  other  words,  the  soil-moisture  content 
at  the  wilting  point  is  not  dependent  to  any  material  degree  upon  the 
age  of  the  plant.  ...  [It]  is  not  materially  influenced  by  the  dryness  of 
the  air,  by  moderate  changes  in  the  solar  intensity,  or  by  differences  in  the 
amount  of  soil  moisture  available  during  the  period  of  growth,  "^o  It 
ranges  for  different  soils  from  less  than  1  per  cent,  in  the  coarsest  sands 
to  as  high  as  30  per  cent,  in  the  heaviest  clays.  "The  use  of  different 
plants  as  indicators  of  the  wilting  point  produces  only  a  relatively  small 
change  in  the  wilting  coefficient  of  a  given  soil.  Representing  the  mean 
value  of  the  wilting  coefficient  of  a  given  soil  by  100,  a  range  from  95 
to  105  approximately,  would  result  from  the  use  of  different  plants 
as  indicators,  .  .  .  The  xerophytes  tested  gave  a  mean  ratio  inter- 
mediate between  the  hydrophytes  and  mesophytes.  This  would  indicate 
that  plants  native  to  dry  regions  are  unable  to  reduce  the  water  content  of 
the  soil  to  a  lower  point  at  the  time  of  wilting  than  is  reached  by  other 
plants.  .  .  .  There  is  evidence  that  drought  resistance  in  a  plant  is  not 
due  to  an  additional  water  supply  made  available  for  growth  by  virtue 
of  a  greater  ability  on  the  part  of  that  plant  to  remove  moisture  from 
the  soil.  "20 

Wilting  Under  Field  Conditions. — The  work  of  Briggs  and  Shantz  on 
wilting  coeflficients  of  different  soils  was  done,  however,  under  fairly 


14  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

uniform  conditions  of  temperature  (about  70°F.)  and  liumidity  (about 
85  per  cent.),  conditions  under  which  the  evaporating  power  of  the  air 
is  low.  In  other  words  the  plants  exhausted  the  water  supply  of  the 
soil  slowly  and  because  of  favorable  atmospheric  conditions  were  actually 
able  to  use  the  last  of  the  "available"  moisture  before  transpiration 
demands  overtook  absorption.  In  the  field,  wilting  does  not  usually 
occur  under  such  favorable  atmospheric  conditions — favorable  from  the 
standpoint  of  soil  moisture  supply. 

It  has  been  found  that  when  atmospheric  conditions  are  such  as  to  promote 
rapid  evaporation,  "the  departure  of  observed  from  calculated  soil  moisture 
contents  at  permanent  wilting  is  extremely  marked  for  all  soils;  permanent 
wilting  in  the  open  occurs  with  a  soil  moisture  content  from  30  to  40  per  cent,  in 
excess  of  that  present  when  the  same  or  similar  plants  are  wilted  in  a  moist 
chamber.  .  .  .  Marked  increase  in  the  evaporating  power  of  the  air  acceler- 
ates the  outgo  of  water  without  producing  a  proportionate  increase  in  its  rate  of 
entrance  from  the  soil.  With  every  increase  in  transpiration  rate  above  a 
certain  Umit,  this  rate  becomes,  therefore,  more  and  more  significant  as  a  factor 
determining  the  extent  to  which  the  soil  water  may  be  exhausted  by  the  plant 
before  the  advent  of  permanent  wilting.  Thus,  permanent  wilting  under  high 
rates  of  evaporation  does  not  at  all  indicate  that  the  available  soil  moisture 
has  been  exhausted.  Instead,  it  merely  indicates  the  reduction  of  the  soil 
moisture  content  to  a  magnitude  which  corresponds  to  the  residue  of  water  left 
in  the  soil  at  the  time  when  excess  of  transpiration  over  absorption  has  brought 
the  entire  plant  into  the  permanently  wilted  condition.  Repeated  determi- 
nations, under  widely  varying  conditions  but  with  relatively  high  evaporation 
rates,  show  that  the  magnitude  of  this  residue  is  directly  related  to  the  intensity 
of  the  evaporating  power  of  the  air."^^ 

It  is  these  higher  wilting  coefficients  under  the  comparatively  high 
transpiration  rates  of  midsummer  which  interest  the  deciduous  fruit 
grower  most  frequently.  Perhaps  the  wilting  coefficient  based  upon  soil 
texture  and  calculated  for  low  transpiration  rates  is  most  important  in 
determining  whether  the  plant  shall  or  shall  not  survive  the  period  of 
drought,  for  before  death  occurs  there  usually  will  be  a  shedding  of 
foliage  and  other  protective  measures  will  be  taken  to  reduce  moisture 
requirements  and  lower  the  transpiration  rate.  On  the  other  hand  the 
effects  of  drought  upon  the  vegetative  activities  of  the  tree  during  the 
summer,  upon  the  size  of  its  fruit  and  upon  the  abscission  of  its  leaves, 
flowers  and  partially  grown  fruit  are  exercised  during  periods  of  very 
high  transpiration  rates.  This  means  that  correspondingly  high  wilting 
coefficients  prevail  and  that  the  aim  of  the  grower  should  be,  as  far  as 
possible,  to  maintain  the  moisture  supply  of  the  soil  well  above  these 
higher  amounts. 

Wilt  171(1  Coefficients  and  Drought  Resistance. — Tables  2,  11  and  12 
compiled  by  Loughridge,  showing  the  minimum  water  requirements  oi 


THE  WATER  REQUIREMENTS  OF  FRUIT  PLANTS 


15 


certain  fruits  in  comparison  with  those  of  certain  other  plants,  are  par- 
ticularly interesting  in  this  connection. 


Table  11. 


-Minimum  Water  Requirements  of  the  Apricot  in  Different  Soils' 
(Records  made  in  early  September) 


Locality 


Condition  of 
trees 


Moisture  in  4  feet  of  soil  (per  cent.) 


Total 


Hygro- 
scopic 


Free 


Tons  of  free 

water  per 

acre 


Dark  loam Sisquoc  Valley . 


Loan 


Loam 

Loam 

Loam 

Loam 

Black  clay.  .  .  . 
Gravelly  loam 


East  of  Ventura  (shallow 
cultivation) 

Ventura  (shallow  culti- 
vation) 

Ventura  (deep  cultivation) 

Los  Berrios  Hill 

Experiment  station 

Niles  (no  cultivation) 

Niles  (cultivation  3  inches) 

Niles  (cultivation  6  inches) 

Woodland 

Woodland 


Sand East  of  Davisville 

Alluvial Davisville 


Good 

5.5 

3.1 

2.4 

Growth  6  inches 

6.5 

5.5 

1.0 

Growth  8  inches 

5.6 

4.2 

1.4 

Growth  36  inches 

9.3 

5.5 

3.8 

Good 

1.7 

0.8 

0.9 

Good 

6.  1 

5.0 

1.1 

Very  poor 

4.4 

4.4 

0.0 

Fair 

5.4 

3.3 

2.1 

Excellent 

6.3 

3.3 

3.0 

Excellent 

18.8 

9.6 

9.2 

Poor 

6.9 

5.0 

1.9 

Good 

4.8 

3.6 

1.2 

Good 

9.0 

6.9 

2.1 

112 
304 
72 
88 
0 
168 
240 
736 
152 
96 
168 


In  commenting  upon  these  tables  Loughridge  states:  "The  apricot,  olive 
and  peach  do  well  on  less  water  than  other  orchard  fruits,  1  per  cent,  of  free 
water  being  sufficient  if  constantly  present.  With  this  amount  the  citrus  fruits, 
pears  and  plums  were  found  to  suffer,  though  the  citrus  fruits  were  in  good  con- 
dition with  a  little  more  water.  The  almond  seems  to  require  about  twice  the 
water  that  the  apricot  does,  while  the  prune  was  found  to  suffer  with  three  times 
the  water  in  which  the  apricot  was  flourishing. 

"  Emphasis  should  be  placed  on  the  fact  that  this  free  water  should  be  present 
throughout  the  soil  to  the  depth  of  4  feet  at  least  and  especially  around  the 
feeding  rootlets  of  the  tree.  The  surface  of  the  soil  may  be  wet,  and  yet  the 
tree  may  suffer  if  the  ground  below  be  so  dry  that  the  rootlets  are  not  able  to 
draw  sufficient  moisture.  This  drying-out  of  the  under-soil  is  one  of  the  evil 
effects  of  a  severely  dry  season,  and  unless  the  rainfall  of  the  succeeding  winter  be 
sufficient  to  penetrate  to  the  depth  of  several  feet  and  moisten  the  soil  around 
the  rootlets  the  trees  will  suffer  almost  as  if  no  rain  had  fallen.  The  same  is 
true  with  regard  to  irrigation ;  those  who  have  to  resort  to  the  artificial  application 
of  water  to  their  lands  because  of  insufficient  rainfall,  should  so  apply  it  that  it 
may  reach  the  tree  rootlets  at  the  depth  of  several  feet  below  the  surface.  This 
is  too  often  not  done,  and  examination  will  show  that  the  water  has,  even  after 
2  days'  irrigation  with  running  water  in  furrows,  not  soaked  down  more  than  10 
or  12  inches,  if  that  much."^^ 

At  first,  it  may  seem  that  the  field  observations  of  Loughridge  are 
not  in  agreement  with  the  conclusion  of  Briggs  and  Shantz  that  the 
wilting  coefficients  are  practically  the  same  for  all  plants  growing  in  the 


16 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Table  12. — Relative  Water  Requirements  of  Different  Fruits  in  Different 

Soils 
(After  Loughridge^') 


Free  water  in 
4  feet  of  soil 

Plants  for  which  the  soil 

moisture  is  just  above  the 

minimum;  cultures  did  well 

Plants  for  which  the  soil 
moisture  is  just  below  the 
minimum;  cultures  suffered 

Percen- 
tage 

Tons  per 
acre 

Sandy  soils — hygroscopic  moisture  1  to  3 

1 
2.0                160 
2.5                200 
3.5                280 

Apricots,  saltbush 
Olives,  peaches,  wheat 

Olives,  peaches,  plums,  grapes 
Cherries,  pears 
Citrus,  prunes 

Sandy  loam  soils — hygroscopic  moisture  3  to  5 

4  to    5 

5  to    6 

400 
480 
560 
640 
720 

Saltbush 
Apricots 

Apricots 

6  to    7 

7  to    8 

Almonds,  plums 
Apples,  olives,  peaches, 
walnuts 

8  to    9 

Loam  soils — hygroscopic  moisture  5 

4  to    5 

5  to    6 

6  to    7 

7  to    8 

400 
480 
560 
640 
720 
800 

Saltbush 

Apricots,  citrus,  figs,  walnuts 

Prunes,  grapes 

Apricots,  almonds 
Prunes 

8  to    9 

9  to  10 

Clay  loams — hygroscopic  moisture  5  to  7 

6  to    7 

7  to    8 

8  to    9 

560 
640 
720 

Peaches,  grapes 

Peaches,  plums 
Wheat 
Sugar  beets 

Clay  soils^ — hygroscopic  moisture  7  to  10 

8  to    9 

9  to  10 

720 
800 
880 
960 
1120 

Apricots 
Grapes 

Figs 

10  to  11 

Wheat 

11  to  12 

Citrus 

12  to  14 

Corn,  sugar  beets 

THE  WATER  REQUIREMENTS  OF  FRUIT  PLANTS  17 

same  soil.  The  greater  tolerance  of  the  apricot,  olive  and  peach  for  drought 
probably  is  not  due  to  a  utilization  of  the  soil  water  in  contact  with  their 
roots  greater  than  that  of  other  plants,  or  in  other  words,  to  the  reduction 
of  the  soil  water  content  to  a  lower  wilting  coeiEficient.  It  is  possibly 
associated  with  a  greater  ability  of  their  roots  to  exploit  every  bit  of  soil 
within  their  range,  or  to  a  wider  range  that  their  roots  may  possess. 
It  is  important  that  both  factors  be  kept  in  mind,  namely,  the  marked 
uniformity  in  the  wilting  coefficient  for  different  plants  and  the  marked 
difference  in  their  ability  to  get  along  on  a  limited  water  supply,  for 
both  are  factors  that  may  alter  materially  cultural  methods,  the  choice 
of  stocks  upon  which  the  fruits  are  grown  and  planting  plans.  As  a  rule 
it  is  not  necessary  to  wait  until  wilting  actually  begins  to  determine  when 
the  danger  point  is  at  hand.  Most  plants  will  show  signs  of  distress 
before  the  moisture  supply  of  the  soil  reaches  its  wilting  coefficient. 
Many  weeds  or  cover  crop  plants  growing  among  the  trees  may  wilt 
noticeably  before  the  trees  give  visible  evidence  of  moisture  deficiency. 
Temporary  v/ilting  at  the  middle  of  the  day  is  quite  likely  to  be  an  indica- 
tion that  the  water  supply  of  the  soil  is  approaching  a  critical  point  and 
efforts  should  be  made  to  deal  with  the  situation  promptly. 

Summary. — Water  is  an  important  plant  constituent,  composing 
from  50  to  85  per  cent,  of  most  living  tissue.  It  is  the  solvent  for  all 
plant  nutrients.  The  intake  of  from  less  than  30  to  more  than  1,000  parts 
of  water  is  required  for  each  part  of  drj^  matter  produced,  the  amount 
varying  with  the  species  and  with  the  conditions  under  which  the  plant 
is  grown,  rWhen  seepage,  run-off  and  evaporation  are  included  this 
means  that  for  the  average  deciduous  fruit  crop  a  precipitation  of  some- 
thing like  30  inches  is  requiredJ  Inability  to  secure  the  requisite  amount 
of  water  checks  growth  and  reduces  yield  and  often  a  relatively  small 
amount  of  additional  available  moisture  at  a  critical  period  will  make 
possible  material  increases  in  the  size  of  the  crop.  Planting  distances 
in  the  orchard  should  be  determined  largely  by  the  available  moisture 
supply  and  the  growing  habits  of  the  particular  species  or  variety.  The 
minimum  water  requirement  of  the  plant,  in  terms  of  units  of  water 
per  unit  of  dry  matter,  is  correlated  with  thorough  acclimatization  and 
optimum  growing  conditions.  Favorable  nutritive  conditions  in  particu- 
lar make  for  water  economy.  The  final  wilting  coefficient  is  practically 
the  same  for  all  plants  in  all  soils,  but  it  varies  greatly  for  the  same  plant 
with  different  soils,  being  low  for  soils  of  coarse  texture  and  very  high 
for  fine  clays.  In  the  field,  temporary  wilting  generally  occurs  before 
the  wilting  coefficient  is  reached,  the  evaporating  power  of  the  air  being 
an  important  determining  factor.  In  practice  it  is  therefore  desirable\ 
to  maintain  the  soil  moisture  supply  well  above  the  wilting  coefficient,'^ 
Different  species  and  varieties  show  considerable  variation  in  their 
ability  to  withstand  drought. 


CHAPTER  II 

THE  INTAKE  AND  UTILIZATION  OF  WATER 

Under  favorable  conditions  the  entrance  of  water  into  the  plant, 
its  translocation  and  its  egress  take  care  of  themselves,  without  conscious 
manipulation  by  the  grower.  At  times,  however,  one  or  another  of 
these  processes  should  be  controlled  to  some  degree  and  pathological 
symptoms  or  conditions  may  arise  which  can  be  understood  only  through 
a  knowledge  of  these  processes. 

WATER  ABSORPTION 

Proper  absorption,  as  the  necessary  prelude  to  the  other  processes, 
is  of  obvious  importance.  Furthermore,  it  is  the  process  with  which  the 
grower  is  most  frequently  brought  into  contact. 

The  Water  Absorbing  Organs. — The  root  is  the  absorbing  system  and 
for  practical  purposes  all  the  water  which  enters  the  plant  is  absorbed 
through  the  root.  There  are  indeed  other  sources  from  which  moisture 
can  be  obtained,  such  as,  for  example,  the  water  resulting  as  an  end  prod- 
uct of  the  oxidation  of  carbohydrates,  which  has  been  termed  metabolic 
water,^  but  such  sources  are  significant  only  in  extreme  circumstances. 
The  absorption  of  water  by  the  root  takes  place  chiefly  through  special 
structures,  the  root  hairs,  which  are  extensions  from  the  epidermal  cells 
of  the  root  a  short  distance  back  of  the  growing  point.  The  absorption 
power  of  the  root  depends  upon  the  extent  of  its  surface  and  it  is  increased 
to  a  marked  degree  by  the  presence  of  root  hairs.  The  ratio  of  the 
surface  of  the  root  supplied  with  hairs  to  one  from  which  the  hairs  have 
been  removed  has  been  calculated  as  5.5  :  1  for  maize  and  in  the  garden 
pea  12.4  :  l.^"^  These  figures  give  some  idea  of  the  efficiency  of  the  root 
hairs  for  water  absorption.  Moisture  can  be  absorbed  by  the  root  tip 
and  also  through  the  surface  of  the  root  for  some  distance  above  the  zone 
of  root  hairs.  In  the  older  portions  of  the  root  the  cortex  and  epidermis 
die  and  peel  off  as  a  result  of  the  formation  of  deep  seated  cork;  hence, 
this  portion  of  the  root  is  incapable  of  absorbing  appreciable  amounts 
of  water. 

The  number  of  root  hairs  varies  with  different  plants  and,  in  the  same 
plant,  with  the  conditions  under  which  it  grows.  Thus,  the  development 
of  root  hairs  is  reduced  in  wet  soil,  or  in  very  dry  soil  and  may  be  entirely 
prevented  where  the  root  is  in  contact  with  water. ^^  This  occurs  in 
certain  plants,  such  as  the  cranberry,  which  normally  grow  in  bogs  where 
the  roots  do  not  develop  root  hairs. 

18 


THE  INTAKE  AND  UTILIZATION  OF  WATER  19 

The  Handling  and  Transplanting  of  Nursery  Stock. — The  practical 
bearing  of  the  point  just  brought  out  upon  the  transplanting  of  fruit 
trees  or  other  plants  is  important.  The  transplanting  of  most  deciduous 
fruit  trees  and  of  many  other  plants  is  usually  accompanied  by  the  loss 
of  a  considerable  part  of  the  large  and  of  the  fibrous  roots  and  by  the 
destruction  of  practically  all  of  the  root  hairs.  New  root  hairs  must  be 
produced  before  active  absorption  can  begin;  these  new  root  hairs  will 
be  formed  only  on  new  branch  rootlets.  This  means  that  if  the  top  of 
the  plant  has  any  considerable  water  requirement  at  the  time  of  trans- 
planting it  will  suffer  for  lack  of  moisture  and  perhaps  wilt  and  die  if  new 
roots  are  not  formed  immediatel3^  The  grower  is  likely  to  place  a  rather 
high  premium  upon  a  large  and  extensive  root  system  in  nursery  trees, 
thinking  that  they  will  surely  absorb  enough  water  to  maintain  the 
moisture  supply  of  the  tops  until  new  roots  are  formed.  A  fairly  ex- 
tensive root  system  in  the  nursery  tree  may  be  an  asset,  but  not  because 
these  roots  devoid  of  root  hairs  are  of  any  material  aid  in  the  direct 
absorption  of  water.  This  explains  wh}'-  tree  roots  pruned  according  to 
the  so-called  Stringfellow  method  at  the  time  of  setting  are  usually  as 
sure  to  take  root  and  grow  as  those  pruned  less  severely,  though  the 
subsequent  growth  may  not  be  so  satisfactory.  More  important  still, 
it  explains  also  why  it  is  desirable  to  prune  back  the  tops  of  most  plants 
at  the  time  of  transplanting  so  as  to  reduce  transpiration  to  a  minimum 
and  prevent  desiccation.  It  shows  furthermore  why  in  climates  not  too 
cold,  fall  transplanted  trees  are  more  likely  to  give  a  good  stand  than 
corresponding  spring-set  trees,  for  during  the  winter  months  new  root 
formation  is  initiated  and  water  can  be  absorbed  in  the  spring  as  fast  as 
the  new  shoots  and  leaves  use  it.^^^  The  spring-set  trees,  on  the  other 
hand,  must  wait  until  new  roots  are  formed  before  they  can  take  up 
moisture  and  if  soil  conditions  remain  imfavorable  for  this  root  formation 
and  atmospheric  conditions  stimulate  vegetative  growth  of  the  top,  the 
pushing  shoots  will  wilt  and  die,  and  the  tree  will  be  lost.  In  the  autumn 
conditions  are  favorable  for  root  growth  for  some  time  after  good  growing 
conditions  for  the  top  have  passed ;  in  the  spring  they  frequently  become 
favorable  for  top  growth  before  or  simultaneously  with  suitable  growing 
conditions  for  the  roots. 

In  the  light  of  the  facts  presented  it  is  not  difficult  to  understand  why  the 
transplanting  of  trees  after  their  buds  have  once  started  in  the  spring  is 
attended  with  very  uncertain  results.  It  is  simplj^  a  case  of  a  demand 
for  water  for  supplying  the  top,  great  in  comparison  with  the  demand 
while  in  the  dormant  stage,  a  demand  that  cannot  be  met  by  the  roots 
because,  temporarily,  they  are  practically  without  absorbing  organs.  If 
it  is  necessary  to  plant  trees  late  in  the  spring,  after  some  vegetative 
growth  may  be  expected  to  take  place,  it  is  well  to  remember  that  the 
transplanted  tree  will  have  practically  no  root  hairs  for  several  days  or 


20  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

even  weeks  after  the  transplanting  operation  and  that,  therefore,  the 
tree  must  be  kept  practically  dormant  until  it  is  actually  planted.  This 
may  be  done  by  holding  it  at  a  low  temperature  in  shade,  or,  if  suitable 
storage  facilities  are  not  available,  by  repeatedly  lifting  and  immediately 
heeling  in  again.  The  effect  of  the  low  temperature  is  to  keep  the  tree 
dormant  because  no  top  growth  will  take  place  at  a  temperature  approxi- 
mating the  freezing  point.  The  effect  of  the  repeated  lifting  and  heeling 
in  again  is  to  check  growth  of  the  top  by  preventing  the  formation  of  new 
roots  and  root  hairs  though  the  temperature  may  be  suitable  for  their 
development  and  thus  cutting  off  the  tree's  water  supply  without  which 
the  shoots  are  retarded. 

It  is  necessary  to  move  evergreen  trees  of  any  considerable  size,  like 
the  pine  or  the  orange  or  the  avocado,  with  a  ball  of  earth  so  that  at  least 
a  moderate  portion  of  the  real  water  absorbing  organs  of  the  plants  are 
retained  and  remain  active;  otherwise,  the  foliage  wilts  or  falls  off  and 
the  plant  is  likely  to  die.  The  facts  that  have  been  presented  explain 
why  excessive  watering  will  not  make  up  for  the  loss  of  roots,  and  particu- 
larly of  root  hairs,  by  trees  transplanted  during  their  growing  season. 
Though  their  remaining  roots  may  be  surrounded  by  a  nearly  saturated 
soil  they  cannot  take  up  appreciable  quantities  of  this  moisture. 

The  Water  Absorbing  Process. — The  process  by  which  water  is  absorbed  by 
the  root  hairs  is  osmosis.  A  plant  cell  such  as  the  epidermal  cell  of  a  root  with  a 
root  hair  attached  has  a  cell  wall  Hned  with  protoplasm  surrounding  a  central 
vacuole.  When  the  root  hair  comes  in  contact  with  the  moisture  of  the  soil  an 
osmotic  system  is  established  and  the  protoplasm  of  the  root  hair  becomes  a 
semi-permeable  membrane  separating  two  solutions,  the  soil  solution  on  the 
outside  and  the  vacuole  on  the  inside.  These  two  solutions  have  different 
concentrations,  that  of  the  vacuole  being  greater  than  that  of  the  soil  solution; 
in  other  words  there  is  less  water  in  the  vacuole  than  in  a  corresponding  volume 
of  soil  solution.  To  equalize  the  concentrations  of  water  on  either  side  of  the 
membrane  water  passes  from  the  soil  into  the  vacuole. 

The  absorption  of  water  in  this  way  by  the  cell  must  increase  the  size  of  the 
vacuole  and  therefore  induce  a  simultaneous  distention  of  the  cell  wall.  Eventu- 
ally the  elasticity  of  the  cell  wall  will  exert  such  a  pressure  on  the  vacuole  that 
no  more  water  can  be  absorbed  and  there  is  a  balance  between  the  elasticity  of 
the  cell  wall  and  the  osmotic  pressure  of  the  cell  contents;  the  cell  is  in  a  state  of 
turgidity.  Under  ordinary  conditions  all  the  living  cells  of  a  plant  are  turgid, 
but  this  turgidity  may  be  lost,  either  by  an  increase  in  the  plasticity  of  the  cell 
wall  or  by  the  loss  of  water  from  the  vacuole.  Either  process  destroys  the 
balance  on  which  turgidity  depends. 

Factors  Enabling  the  Root  to  Exploit  the  Soil. — Several  factors  cooperate  in 
enabling  the  plant  to  exploit  the  moisture  content  of  the  soil.  The  root  hairs  are 
continuously  formed  anew  at  a  certain  distance  from  the  tip  of  the  growing  root 
so  that  a  new  supply  is  produced  as  fast  as  the  older  root  hairs  die.  As  these 
extend  into  untouched  portions  of  the  soil,  the  roots  are  continually  pushing  into 


THE  INTAKE  AND  UTILIZATION  OF  WATER  21 

new  soil  throughout  the  growing  season,  leaving  those  regions  from  which  they 
have  already  drawn  their  water  and  nutrient  supply. 

Furthermore,  the  absorbing  capacity  of  the  root  hairs  is  not  limited  to  that 
portion  of  the  soil  with  which  they  come  in  immediate  contact.  As  the  root 
hair  withdraws  moisture  from  the  water  films  about  the  soil  particles,  these  films 
become  thinner  than  those  about  neighboring  soil  particles.  Since  surface 
tension  maintains  an  equilibrium  between  the  amounts  of  water  on  contiguous 
surfaces,  water  tends  to  distribute  itself  evenly.  As  a  result  it  flows  toward 
those  parts  of  the  soil  from  which  water  has  been  withdrawn,  hence,  in  the 
direction  of  the  root  hairs.  In  this  way  the  individual  root  hair  is  capable  of 
absorbing  water  which  is  a  considerable  distance  away  from  it. 

The  movement  of  the  roots,  which  their  growth  in  length  brings  about,  is 
likewise  a  movement  in  a  definite  direction,  for  the  root  tip  is  sensitive  to  differ- 
ences in  the  amount  of  moisture  present  on  opposite  sides  and  responds  to  this 
difference  by  bending  toward  that  side  where  there  is  more  moisture."  By  this 
means  roots  grow  toward  those  portions  of  the  soil  which  have  the  optimum 
water  content. 

Adaptation  of  Roots  to  Moisture  Conditions. — In  addition  to  the  factors 
already  discussed  the  adaptability  of  the  root  system  to  the  condition  of  the 
soil  is  important  in  enabling  the  plant  to  obtain  a  maximum  supply  of  water. 
A  small  water  content  of  the  soil,  within  certain  limits,  stimulates  the  roots  to 
greater  development,  resulting  in  a  greatly  increased  absorbing  surface.  In 
spite  of  this  greater  surface,  however,  the  supply  of  water  is  often  restricted 
and  the  portion  of  the  plant  above  ground  is  not  capable  of  much  development. 
In  one  investigation  the  ratio  of  roots  to  tops  for  oats,  grown  in  dry  soil,  was  found 
to  be  1:7.4  and  in  wet  soil  1:16.16.^'^^  In  this  second  instance  the  roots 
remained  small  because  the  optimum  conditions  for  moisture  were  exceeded. 
These  figures  give  some  indication  of  the  correlation  which  exists  between  root 
and  shoot  development  though  the  relation  may  be  quite  different  in  other 
plants  and  under  other  conditions.  The  accommodation  of  roots  to  soil  con- 
ditions varies  with  different  species.  Thus  Weaver^^^  finds  that  7  out  of  10  species 
investigated  by  him  respond  to  changed  environmental  conditions.  Pulling^"^ 
states  that  characteristically  shallow  rooted  plants  such  as  Picea  Mariana, 
Larix  laricina  and  Betula  alba  papyrifera,  as  well  as  the  more  deeply  rooted 
Pinus  Strobus  and  P.  Banksiana  do  not  adapt  themselves,  while  the  shallow 
rooted  Picea  canadensis  and  the  deeply  rooted  Popidus  balsamifera  exhibit  con- 
siderable plasticity.  In  another  place  the  root  distribution  of  orchard  trees  is 
discussed  in  greater  detail  and  some  of  its  relations  to  water  supply  are  mentioned 
in  that  connection. 


Factors  Influencing  Rate  of  Absorption. — The  ability  of  plants  to 
absorb  water  depends  upon  the  absorbing  surface  of  their  roots  and  on 
the  following  external  factors:  the  power  of  the  soil  to  deliver  water,  the 
temperature  and  aeration  of  the  soil,  its  chemical  properties  and  the 
concentration  of  the  soil  solution.  Other  things  being  equal  the  higher 
the  temperature  the  greater  the  absorption  until  a  certain  optimum  value 
is  reached;  temperatures  above  this  optimum  retard  water  absorption. 


22  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Though  water  absorption  is  greatly  reduced  at  low  temperatures  many 
plants  are  able  to  take  up  water  when  the  soil  temperature  is  below  0°C., 
for  even  at  —3  or  —  4°C,,  much  of  the  soil  water  is  not  frozen  and  the  soil 
is  still  capable  of  delivering  water  to  the  root  surface. ^^ 

The  amount  of  oxygen  in  the  soil  air  has  a  marked  effect  on  root 
absorption;  if  for  any  reason  the  supply  of  oxygen  is  inadequate,  absorp- 
tion ceases.  It  should  be  remembered,  however,  that  oxygen  dissolved 
in  the  soil  water  is  available  to  the  root  system.  In  fact,  the  oxygen 
absorbed  by  the  living  cells  of  the  root  must  be  dissolved  in  water  before 
it  can  be  taken  up.  The  susceptibility  of  the  roots  to  differences  in  the 
oxygen  supply  varies  markedly  with  different  plants.  Thus  roots  of 
Coleus  Blumei  and  Heliotropium  peruvianum  showed  injury  after  three 
days'  exposure  to  a  soil  atmosphere  mixed  with  25  per  cent,  nitrogen 
gas,  while  roots  of  Salix  sp.  grew  freely  in  pure  nitrogen. ^^  There  is  some 
indication  that  roots  of  deeper  penetration  are  less  responsive  to  changes 
in  aeration  and  temperature  than  the  more  superficial  roots. 

The  effect  upon  top  growth  of  reduced  absorption  by  the  roots  occasioned 
by  poor  aeration  incident  to  a  condition  of  the  soil  approaching  saturation,  is 
strikingly  illustrated  by  the  behavior  of  established  trees  of  certain  kinds  in 
portions  of  India.  Howard  and  Howard^^  record  that  these  trees  naturally 
have  a  short  resting  period  during  midwinter,  a  period  often  accompanied  or 
preceded  by  leaf  fall.  With  a  rise  in  temperature  during  February,  new  leaves, 
shoots  and  flowers  are  formed  and  rapid  growth  continues  until  hot  weather 
checks  it.  A  second  period  of  rapid  vegetative  growth  is  inaugurated  with  the 
advent  of  the  monsoon,  but  when  the  soil  approaches  saturation,  growth  slows 
down  again  or  nearly  ceases.  There  is  a  third  period  of  vegetative  activity  at 
the  and  of  the  monsoon  when,  with  the  drying  out  of  the  soil,  the  attendant 
aeration  makes  increased  root  activity  possible.  This  third  period  of  growth  is 
finally  checked  by  the  low  temperature  of  the  winter  season. 

Transpiration  (and  hence  absorption)  is  decreased  by  the  addition  of  small 
amounts  of  tartaric,  oxalic,  nitric,  or  carbonic  acid  to  the  soil  and  is  increased 
by  alkalies,  such  as  potash,  soda,  or  ammonia,  though  under  field  conditions 
these  factors  are  apt  to  be  of  minor  importance. ^^  An  increase  in  the  concen- 
tration of  the  soil  solution  likewise  decreases  water  absorption  by  its  effect  on 
the  osmotic  process.     Such  effects  probably  vary  greatly  with  different  plants. 

Submergence  and  Root  Killing. — The  effects  of  submergence  on  decidu- 
ous fruit  plants  are  due  primarily  to  the  diminished  aeration  of  the  roots 
which  this  ordinarily  involves.  It  has  been  found  that  certain  land  plants 
with  submerged  roots  absorb  water  more  rapidly  at  first  but  that  later 
the  rate  of  absorption  falls  off  to  a  marked  degree,  the  plants  wilt  and 
after  a  few  days  the  leaves  become  yellow  and  drop.^^  After  prolonged 
submergence  the  roots  below  the  surface  die  and  no  new  roots  develop; 
eventually  the  entire  plant  succumbs.  All  of  these  effects,  however, 
were  alleviated  or  eliminated  when  the  roots  were  submerged  in  aerated 


THE  INTAKE  AND  UTILIZATION  OF  WATER  23 

water.  Under  these  conditions  some  plants  have  survived  submergence 
for  three  weeks.  The  roots  hved  in  this  aerated  water  but  grew  more 
slowly  and  in  some  cases  root  hairs  developed.  Even  the  roots  of  the 
cocoanut,  though  often  found  in  a  practically  saturated  soil,  are  sensitive 
to  a  lack  of  aeration,  for  thej^  thrive  only  if  the  water  bathing  them  is 
continually  moving  and  they  die  if  it  is  stagnant.^  It  is  not  the  water 
but  the  lack  of  air  in  standing  water  that  is  harmful.  The  submergence 
to  wliich  the  roots  of  orchard  trees  are  occasionally  subject  in  certain 
locations  is  of  a  type  that  is  generally  accompanied  by  a  lack  of  aeration. 
The  result  is  a  prompt  killing  of  the  root  hairs,  followed  more  or  less 
closely  by  the  death  of  the  roots  themselves.  This  is  likely  to  be  the 
case  when  roots  are  submerged  by  the  rise  of  the  ground  water  in  irrigated 
sections  and  in  orchards  planted  in  low-lying  poorly  drained  ground.  It 
is  not  so  apt  to  be  the  case  with  trees  planted  on  low  but  well  drained 
bottom  lands,  or  alluvial  soils  subject  to  occasional  overflow  of  short 
duration  during  periods  of  flood.  Even  in  the  latter  instance,  however, 
it  is  noteworthy  that  the  trees  are  apt  to  be  severely  injured,  or  killed, 
if  the  roots  are  submerged  for  more  than  several  days  during  the  growing 
season  or  for  a  period  of  as  many  weeks  during  their  dormant  season. 
Certain  bog  plants  like  the  swamp  blueberry  and  cranberry,  however, 
will  stand  complete  submergence  of  their  root  systems  for  a  period  of  four 
of  five  months  during  the  winter,  though  submergence  of  as  many  days 
during  the  growing  season  is  attended  with  great  risk.^''  There  is  good 
reason  to  believe  that  many  of  the  troubles  variously  attributed  to 
winter  injury,  drought  and  soil  infertility  may  be  end  products  of  tempo- 
rary root  submergence  that  leads  immediately  to  a  kind  of  root  pruning. 
It  should  be  realized  that  root  systems  may  be  submerged  though  no 
water  stands  on  the  surface  of  the  soil.  More  attention  is  devoted  to  this 
phase  of  the  subject  in  a  later  chapter  of  this  section  and  in  the  section 
on  Temperature  Relations. 

TRANSPIRATION 

Large  quantities  of  water  are  lost  by  evaporation  from. the  portions 
of  the  plant  above  ground  and  particularly'-  from  the  leaves.  Duggar*^ 
estimates  that  an  apple  tree  30  years  old  might  lose  250  pounds  of  water 
a  day  or  possibly  36,000  pounds  a  season.  At  this  rate  an  acre  of  40 
trees  would  represent  a  water  elimination  of  600  tons  a  year.  This 
water  loss  from  plants  is  not  strictly  a  physical  process  of  evaporation, 
because  it  is  influenced  by  factors  such  as  light  and  is  subject  to  some 
degree  of  modification  by  the  plant.  Since  evaporation  is  not  affected 
in  the  same  way  by  these  factors  the  water  loss  of  plants  must  be  con- 
sidered a  physiological  process;  hence  it  is  designated  transpiration. 
Whether  transpiration  performs  any  useful  role  in  aiding  the  process 
of  absorption  of  mineral  constituents,  or  in  lowering  the  temperature 


24 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


.'Pbf  the  leaves  is  an  open  question.  The  generally  accepted  opinion  is 
SSthat  transpiration  is  a  necessary  evil  rather  than  an  advantage  to  the 
;^plant. 

.  %t  Cuticular  and  Stomatal  Transpiration  Compared. — Transpiration  is 
jgof  two  kinds;  a  small  amount  of  water  is  lost  from  the  cuticular  surface 
*^of  the  leaf,  but  by  far  the  greater  proportion  is  lost  through  the  stomata. 
^Some  measure  of  the  proportion  between  these  is  furnished  by  the  data 
'^presented  in  Table  13. 


Table    1.3.— Relation    Between 

5TOMATAL    Distribution    and 

Trans  filiation 

Stomata  per  square  millimeter 

Water  transpired  in  24  hours  from 
20    square    centimeters 

Upper  surface 

Lower  surface 

Upper  surface 
(grams) 

Lower  surface 

(grams) 

Pear 

Apple 

0 
0 
0 
0 
0 

253 

246 

14.5 

25 

60 

5 
20 

Red  currant 

Canna 

35 

Linden 

49 

The  amount  of  cuticular  transpiration  is  relatively  constant  while  the  amount 
of  stomatal  transpiration  can  be  regulated  by  the  activity  of  the  stomatal  guard 
cells.  In  sunlight  these  cells  manufacture  sugars  by  means  of  the  chloroplasts 
which  they  contain  and  thereby  increase  their  osmotic  concentration  so  that  they 
absorb  water  from  the  surrounding  tissue  and  increase  in  turgidity.  The  walls 
of  the  guard  cells  are  peculiarly  thickened  so  that  when  the  cells  are  turgid,  the 
stomatal  aperture  is  open  and  when  turgidity  is  lost  the  aperture  is  closed.  The 
guard  cells  are  likewise  sensitive  to  light  stimuli,  to  which  they  respond  by  changes 
in  turgidity  more  rapid  than  those  produced  in  the  manner  just  described. 

The  water  lost  by  transpiration  from  the  leaves  first  evaporates  from  the 
surface  of  the  mesophyll  cells  in  the  interior  and  collects  as  water  vapor  in  the 
intercellular  spaces.  This  water  vapor  then  passes  from  the  intercellular  spaces 
of  the  leaf  through  the  stomatal  apertures  to  the  outside.  This  is  largely  a 
process  of  diffusion  and  follows  Brown  and  Escombe's  Law  which  states  that 
diffusion  through  an  aperture  is  proportional  to  the  radius  and  not  to  the  area  of 
the  aperture.  Thus  the  diffusion  which  might  take  place  through  10  small 
apertures  with  a  radius  of  1  millimeter,  would  be  equal  to  the  diffusion  which 
could  take  place  through  one  aperture  with  a  radius  of  1  centimeter.  It  is 
evident  that  if  the  apertures  are  sufficiently  small  and  are  scattered  over  a  surface 
in  such  a  way  that  the  diffusion  through  one  does  not  interfere  with  that  through 
another,  then  diffusion  through  such  a  perforated  surface  will  take  place  as  if  no 
surface  were  present.  When  the  apertures  are  distributed  over  a  surface  so  that 
they  are  about  10  diameters  distant  from  one  another,  the  maximum  amount  of 
diffusion  is  possible.  This  proportion  holds  roughly  for  the  distribution  of  the 
stomata  in  most  leaves.  It  is  evident  that  when  the  stomata  are  opened  the 
surface  of  the  leaf  offers  little  or  no  resistance  to  the  diffusion  of  water  vapor. 


THE  INTAKE  AND   UTILIZATION  OF  WATER 


25 


but  that  when  the  stomata  are  closed  transpiration  practically  ceases  except  for  .  • 
cuticular  water  loss.  ^ , 

Variabilitii  in  Number  of  St07nata  in  Accordance  with  External  Condi-    . 
iions. — The  number  of  stomata  on  the  leaf  surface  is  not  determined  .*" 
in  the  unopened  bud,  but  varies  with  the  conditions  under  which  the 
leaf  develops. 

Table  14  presents  data  showing  the  reduction  in  the  number  of  stomata  -" 
per  square  millimeter  when  the  available  water  supply  in  the  soil  is  reduced. 
Though  the  reduction  in  the  number  of  stomata  per  unit  of  leaf  surface 
is  not  exactly  proportional  to  the  reduction  in  soil  moisture,  there  is  a  very 
material  decrease,  indicating  a  marked  ability  on  the  part  of  the  plant  to  adjust 
itself  to  its  water  supply.  This  flexibility  is  perhaps  one  of  the  reasons  why 
many  plants  are  able  to  thrive  under  wide  ranges  of  soil  moisture  and  atmospheric 
humidity. 

Table  14. — The  Influence  of  Soil  Moisture  Upon  Number  of  Stomata 

{After  Duggar*^) 


Percentage  of  water 

Stomata  per  square  millimeter 

in  sand 

Corn 

Wheat 

38 

181 

103 

30 

130 

85 

20 

129 

82 

15 

124 

81 

11 

107 

59 

However,  the  number  of  stomata  cannot  be  modified  after  the  leaf 
once  attains  full  size.  This  means  that  its  ability  to  adapt  itself 
in  this  way  to  extremes  of  soil  or  atmospheric  moisture  must  be  exercised 
early  in  the  season.  Foilage  developing  in  the  spring  on  a  plant  in  a 
moisture  laden  soil  will  probably  transpire  somewhat  more  per  unit  of 
area  later  in  the  season,  than  it  would  had  it  developed  under  drier 
conditions,  though  the  increase  will  probably  not  be  proportional  to 
the  increase  in  number  of  stomata.  However,  the  extra  amount  of  water 
required  by  such  plants  during  the  summer  is  due  mainly  to  the  in- 
creased leaf  area.  If  trees  are  so  handled  early  in  the  season  as  to  develop 
large  water  requirements  the  cultivator  should  recognize  the  fact  that 
this  demand  will  be  more  or  less  continuous  through  the  summer  and 
shape  his  cultural  practices  accordingly. 

Factors  Influencing  Rate  of  Transpiration. — The  rate  of  transpiration 
is  influenced  by  a  number  of  factors,  such  as  the  character  of  the 
cuticle,  the  age  of  the  leaf,  defoliation,  wind  velocity,  light  and  tempera- 
ture. 


26  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Character  of  Cuticle. — The  cuticular  water  loss  of  plants  is  affected  materially 
by  the  thickness  and  character  of  the  cuticle.  The  presence  of  a  waxy  coating 
diminishes  the  amount  of  water  loss.  The  effectiveness  of  such  a  coating  may  be 
seen  from  data  given  by  Boussingault^®  which  show  that  an  apple  loses  0.05 
grams  of  water  per  cubic  centimeter  per  hour  through  its  cuticle,  but  that  when 
the  cuticle  is  removed  it  loses  0.277  grams  or  55  times  as  much  from  the  same 
surface.  Cork  is  also  an  effective  protection  against  water  loss.  A  peeled 
potato  loses  water  64  times  as  rapidly  as  an  unpeeled  potato. ^"^ 

Age  of  Leaf. — The  amount  of  transpiration  from  a  leaf  hkewise  varies  with 
age.  The  youngest  leaves  transpire  most  for  the  cuticle  is  thin  and  permeable; 
as  the  leaf  grows  older  the  cuticle  thickens  and  permeabiUty  decreases,  and  with 
it  the  rate  of  transpiration.  Later  this  rate  rises  to  a  second  maximum,  lower 
than  the  first,  as  the  result  of  the  development  and  functioning  of  the  stomata. 
Then  as  the  leaf  ages  further  there  is  another  decline  in  the  rate  of  transpiration 
due  possibly  to  changes  in  the  properties  of  the  epidermis. 

Defoliation.  Summer  Pru7iing. — Data  presented  in  Table  15  show 
that  the  rate  of  transpiration  is  also  affected  by  defoliation.  This  indi- 
cates that,  though  midsummer  or  late  summer  pruning  to  protect  a 
plant  and  its  fruit  from  drought  injury  will  reduce  its  water  requirements 
somewhat,  the  reduction  will  not  be  directly  proportional  to  the  percent- 
age of  the  foliage  that  is  removed. 

Tabt-e  15. — The  Influence  of  Defoliation  Upon  Rate  of  Transpiration  in  a 

5-YEAR  Old  Fir  Tree 

(After  Hartig  ^^) 

Percentage  Evaporation  per  Square  Meter  of 

OF  Foliage  Surface  (Grams) 

100  270 

60  272 

30  460 

10  607 

Wind  Velocity/.  Windbreaks. — The  agencies  thus  far  mentioned  as 
affecting  rate  of  transpiration  have  been  internal  to  the  plant.  Various 
external  factors  also  have  their  effects.  The  most  important  of  these 
external  factors  are  atmospheric  humidity,  wind,  light  and  temperature, 
which  together  determine  the  evaporating  power  of  the  air.  It  has  been 
found  that  the  rate  of  water  loss  is  a  simple  linear  function  of  the  evapo- 
rating power  of  the  air  and  that  the  leaf  gives  off  water  as  if  the  water 
were  at  a  temperature  about  1°C.  higher  than  the  surrounding  air.^" 

Water  loss  in  wind  is  greater  than  in  still  air.  This  is  brought  out 
by  the  data  presented  in  Table  16.  Attention  has  been  called  already  to 
the  fact  that  one  of  the  functions  of  the  windbreak  is  to  reduce  the  water 
requirement  of  the  plants  in  its  shelter.  Probably  the  decrease  in  the 
amount  of  water  required  for  a  given  unit  of  dry  matter  is  not  directly 
proportional  to  the  lessened  rate  of  transpiration  consequent  upon  de- 


THE  INTAKE  AND   UTILIZATION  OF  WATER 


27 


creased  wind  velocity,  but  in  both  cases  the  saving  of  water  is  great 
enough  to  be  of  real  importance  in  plant  production. 

Table   16. — The  Influence  of  Wind  Velocity  Upon  Rate  of    Transpiration 

(After  EberfW) 


Wind  velocity 

Evaporation  in  5  minutes  from  free-moving 

Check  in  still   air 

second)                                                humidity 

Before  (Grams) 

After  (Grams) 

2 
3 

5 

0.593 
0.631 
0.638 

0.371 
0.358 
0.361 

0.311 
0.320 
0.319 

Light. — In  its  lower  ranges  increased  illumination  has  been  found  to  cause 
increased  transpiration  irrespective  of  the  action  of  the  guard  cells  already- 
discussed. '*''  The  effect  of  light  may  be  due  to  absorption  of  radiant  energy  or  to 
increased  permeability  of  the  membranes.  The  heat  set  free  by  chemical  proc- 
esses or  received  by  radiation  may  pass  directly  into  the  latent  form  without 
effecting  a  rise  in  the  tempeature  of  the  leaf:  that  is,  it  may  be  used  completely 
in  vaporizing  water.  Protoplasmic  membranes  are  more  permeable  in  light 
than  in  darkness  and  the  same  seems  to  hold  for  the  non-cutinized  cell  wall.^^ 

This  increased  rate  of  transpiration  produced  by  exposure  to  hght  probably 
accounts  for  the  characteristic  action  of  illumination  in  retarding  the  rate  of 
growth  and  the  dependence  of  green  plants  upon  hght  for  the  differentiation  of 
tissues. ^^  The  gradual  reduction  in  the  osmotic  concentration  of  the  stomatal 
guard  cells  found  by  Wiggins^^^  may  also  be  attributed  to  increased  permeabihty 
after  exposure  to  hght.  In  the  afternoon  the  manufacture  of  soluble  carbohy- 
drates is  apparently  more  than  offset  by  the  increased  permeabihty.  Hence, 
the  osmotically  active  substances  in  the  guard  cells  diffuse  into  the  adjoining 
cells,  the  guard  cells  lose  their  turgidity  and  the  stomata  close  soon  after  dark- 
ness sets  in. 

Temperature.  Slope  of  Ground. — The  rate  of  transpiration  increases 
with  rising  temperature.  It  is  one  of  the  reasons,  though  probably  not 
the  main  reason,  why  north  slopes  may  be  preferable  to  south  slopes 
when  moisture  is  a  limiting  factor.  It  likewise  furnishes  the  explanation 
of  most  of  the  phenomena  connected  with  the  temporary  wilting  and  later 
recovery  of  turgidity  in  plants.  Of  particular  interest  is  the  effect  of 
temperatures  below  0°C.  on  the  transpiration  from  twigs.  The  data 
presented  in  Table  17  on  the  transpiration  from  a  branch  of  Taxus  haccata 
from  which  the  leaves  had  been  removed  are  interesting  not  only  in  show- 
ing the  influence  upon  transpiration  of  an  increase  in  temperature,  but 
also  in  showing  that  transpiration  takes  place  at  temperatures  consider- 
ably below  the  freezing  point.  Water  loss  under  these  conditions  is 
associated  with  certain  types  of  winter  injury,  a  matter  discussed  in 
more  detail  in  another  section. 


28  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Table    17. — The   Influence   of   Temperature   Upon   Rate   of   Transpiration 

{After  Burgerstein^^) 

Water  Transpired  per  Hour  (in  Per  Cent. 
Average  Temperature  (Centigrade)  .  of  Weight  op  Branch) 

-  2.0  0.288 

-  2.8  0.227 
-•5.2  0.131 

-  5.7  0.127 

-  6.2  0,093 

-  6.8  0.028 
-10.7  0.019 

THE  WATER  CONDUCTING  SYSTEM   OF  THE  TREE 

The  conduction  of  water  from  the  roots  to  the  leaves  has  been  investigated 
by  Dixon,"  from  whom  the  following  account  is  largely  taken.  The  water 
absorbed  by  the  root  hairs  passes  by  osmosis  from  cell  to  cell  through  the  cortex 
of  the  root  and  into  the  cavities  of  the  wood  cells.  It  then  passes  through  the 
younger  layers  of  wood  from  the  roots  through  the  trunk  to  the  branches  and 
eventually  to  the  tracheae  of  the  leaf.  From  these  cells  it  is  abstracted  by  the 
endodermis  and  eventually  finds  its  way  by  osmosis  to  the  mesophyll  cells  from 
whose  outer  surfaces  it  evaporates.  Water  passes  into  the  cavities  of  the  wood 
cells  in  the  root  by  osmosis.  The  osmotic  system  involved  here  consists  of  the 
water  of  the  soil,  the  solution  in  the  elements  of  the  wood,  and  the  cortical  cells 
of  the  roots  which  constitute  the  semi-permeable  membrane  separating  these 
two  solutions.  These  cortical  cells  have  a  higher  osmotic  pressure  than  the 
tracheae  but,  being  fully  distended,  they  function  merely  as  a  complex  membrane 
across  which  a  flow  of  water  takes  place.  The  concentration  of  the  solution 
which  fills  the  tracheae  is  higher  than  that  of  the  soil  solution  and  is  maintained 
by  the  secretion  of  sugars  from  the  wood  parenchyma  cells  with  which  they  come 
in  contact.*  This  osmotic  system  may  develop  considerable  pressure  and  result 
in  the  exudation  of  Uquid  from  cut  surfaces  as  in  the  well  known  phenomenon 
of  bleeding  in  the  vine. 

After  the  water  has  entered  the  wood  cells  in  the  root,  it  is  carried  up  in  the 
woody  tissue  in  an  unbroken  column,  which  extends  into  the  veinlets  of  the 
leaf.  The  water  in  the  conducting  tracts  of  high  trees  hangs  there  by  virtue  of 
cohesion.  It  must  not  enclose  bubbles,  which  would  break  the  column  of 
water  and  permanently  interfere  with  conduction.  The  structure  of  woody 
tissue  may  be  considered  a  special  adaptation  which  confers  stability  on  the 
transpiration  stream  and  prevents  bubbles  which  may  develop  from  occupying 
more  than  an  infinitesimal  part  of  the  cross  section  of  the  whole  water  current. 
The  imbibitional  properties  of  the  walls  of  neighboring  water-filled  tracheae 
render  the  water  continuous  between  them.  If  a  bubble  develops  anywhere  in 
the  transpiration  stream  it  will  enlarge  until  it  fills  the  cavity  of  the  cell  in  which 
it  originated,  but  the  walls  of  the  tracheae  limit  the  bubble  and  prevent  its  further 
expansion.  From  these  considerations  it  follows  that  the  column  of  water 
will  not  be  broken  unless  a  very  large  number  of  the  conducting  tubes  contain 
air.  Despite  its  mobiUty  the  water,  as  it  rises  in  the  wood,  behaves  very  much 
like  a  rigid  body. 


THE  INTAKE  AND  UTILIZATION  OF  WATER  29 

The  vessels  may  be  considered  as  the  path  of  the  most  rapid  portion  of  the 
transpiration  stream.  The  tracheids  transmit  water  more  slowly  but  continue 
to  function  when  the  water  supply  is  limited.  Though  the  internal  thickenings 
on  the  walls  of  the  trachea?  are  essential  for  the  transmission  and  stabiHty  of  a 
stream  under  tension,  the  whole  wall  is  not  uniformly  thickened  because  the  per- 
meability of  the  thinner  portions  is  necessary.  The  flow  of  water  is  further 
facilitated  by  the  presence  of  bordered  pits,  which  are  themselves  remarkably 
adapted  to  permit  a  flow  of  water  under  proper  conditions  and  to  prevent  the 
expansion  of  bubbles  beyond  the  Hmits  of  a  single  cell.  The  membrane  and  torus 
of  each  bordered  pit  is  able  to  take  up  three  positions,  a  median  position  when 
it  is  not  acted  upon  by  lateral  forces  and  two  lateral  positions  when  the  membrane 
is  deflected  against  one  dome  or  the  other.  When  adjacent  cells  are  filled  with 
water,  the  membrane  assumes  the  median  position  and  permits  a  flow  of  water 
through  the  delicate  membrane  which  surrounds  the  torus.  When  a  bubble 
develops  in  the  trachea  and  gradually  distends  until  it  fills  it,  the  membranes  of 
the  pits  in  the  walls  of  the  trachea  become  deflected  away  from  the  bubble,  until 
the  torus  hes  over  the  perforation  in  the  dome  like  a  valve  in  its  seat.  In  this 
position  the  tension  of  the  water  on  the  one  side  and  the  pressure  of  the  gas  on 
the  other  are  withstood. 

The  water  after  it  reaches  the  tracheae  of  the  leaf  is  drawn  into  the  leaf  cells 
by  osmosis.  Thus  the  entire  transpiration  stream  is  raised  by  the  activity  of  the 
leaf  cells.  According  to  Dixon''^  these  cells  actually  secrete  the  water  and  it  is 
removed  by  evaporation  from  their  outer  surfaces.  The  resistance  encountered 
by  the  current  of  water  in  passing  through  the  wood  at  the  velocity  of  the  trans- 
piration stream  is  probably  equivalent  to  a  head  of  water  equal  in  length  to  the 
wood  traversed.  Hence,  the  tension  needed  to  raise  the  transpiration  stream 
in  a  tree  must  equal  the  pressure  of  a  head  of  water  twice  as  high  as  the  tree. 
In  a  tree  100  meters  high,  for  example,  a  tension  of  20  atmospheres  is  needed. 
Dixon  finds  the  cohesion  of  sap  to  be  at  least  200  atmospheres,  so  that  it  is  in  no 
way  taxed  by  the  tension.  He  also  finds  that  the  osmotic  concentration  of  the 
mesophyll  cells  is  adequate  to  resist  the  transpiration  tension  and  is  in  many 
cases  much  in  excess  of  that  required.  Finally,  he  shows  that  the  energy  set 
free  by  respiration  in  the  leaves  is  sufficient  to  do  the  work  of  secretion  against 
the  resistance  of  the  transpiration  stream. 

Summary. — The  total  system  of  water  absorption,  conduction  and 
transpiration  is  more  or  less  a  unit.  As  a  rule  water  is  absorbed  only  to 
replace  water  lost  by  transpiration  and  in  the  long  run  the  amounts  of 
each  are  equal.  For  short  periods,  however,  transpiration  may  slightly 
exceed  absorption.  The  chief  factors  determining  the  flow  of  water 
through  the  plant  are  the  available  water  supply  and  transpiration.  If 
for  any  reason  more  water  is  transpired  than  is  absorbed  and  this  condi- 
tion continues  for  any  length  of  time,  the  cells  lose  their  turgidity  and  the 
plant  wilts.  If  the  supply  of  water  is  renewed  in  time,  the  plant  recovers 
its  turgidity  without  ill  effects,  but  prolonged  wilting  is  attended  by 
serious  disturbances  and  eventually  results  in  death. 

Nursery  stock  loses  its  water-absorbing  organs,  the  root  hairs,  upon 


30  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

digging  and  should  be  so  handled  until  permanently  planted  that  the 
buds  cannot  start.  Plants  in  leaf  should  be  moved  with  a  "ball  of 
earth."  In  most  deciduous  fruits  aeration  of  soil  is  necessary  for 
absorption  and  continued  submergence  leads  to  the  death  of  root  hairs 
and  roots.  Plants  developing  in  the  spring  under  circumstances  such 
that  they  have  large  water  requirements, .  continue  to  demand  large 
amounts  throughout  the  season  and  cultural  operations  should  be  shaped 
accordingly.  Summer  pruning  may  reduce  water  requirements  some- 
what, but  the  reduction  is  not  proportional  to  the  loss  of  foliage.  Some 
protection  against  water  loss  may  be  afforded  by  windbreaks  and  the 
choice  of  northern  slopes. 


CHAPTER  III 

ORCHARD  SOIL  MANAGEMENT  METHODS  AND  MOISTURE 
CONSERVATION 

Most  cultural  practices  which  involve  the  orchard  soil  are  for  the 
purpose  of  influencing  more  or  less  directly  its  moisture  supply  or  its 
productivity.  It  is  well,  therefore,  at  this  point  to  examine  somewhat 
carefully  into  the  ways  in  which  the  several  cultural  practices  commonly 
employed  in  the  fruit  plantation  affect  the  water  content  of  its  soil, 
for  though  they  must  be  considered  also  as  they  influence  soil  chemistry, 
they  concern  water  supply  even  more  directly.  In  general  farm  practice, 
certain  soil  treatments  are  given  with  the  purpose  of  reducing,  at  least 
temporarily,  the  water  content  of  the  soil.  In  the  orchard,  however, 
excess  moisture  is  taken  care  of  by  surface  run-off  and  by  natural  or 
artificial  underdrainage  if  the  orchard  has  been  well  located.  The 
efficiency  of  orchard  soil  management  methods,  therefore,  is  to  be  judged 
by  the  way  in  which  they  conserve  moisture  rather  than  by  the  way  in 
which  they  dissipate  it,  though  in  some  sections  there  may  be  occasion 
to  dry  out  the  soil  in  the  fall  for  the  purpose  of  hastening  maturity. 

Orchard  Soil  Management  Methods  Defined  and  Described. — 
The  commonly  recognized  and  more  or  less  distinct  methods  of  soil 
management  in  the  orchard  may  be  listed  as  follows:  (1)  clean  culture, 
(2)  clean  culture  with  cover  crop,  (3)  artificial  mulch,  (4)  sod  mulch, 
(5)  sod,  (6)  intercropping.  There  are  almost  endless  combinations 
and  forms  of  treatments  intermediate  between  any  two  of  these  methods; 
consequently  it  is  nearly  impossible  to  differentiate  clearly  between  them. 
For  instance,  clean  cultivation  may  be  practiced  in  the  orchard  until 
the  first  of  August.  If  the  land  remains  fairly  clean  and  free  from  weed 
growth  during  the  fall  and  winter  months,  the  orchard  is  said  to  be 
under  the  clean  culture  method  of  management.  If  no  cover  crop  were 
seeded,  but  a  heavy  growth  of  weeds  comes  in  and  serves  as  a  fall  and 
winter  cover,  the  orchard  is  practically  under  a  cover  crop  method  of 
management,  though  many  growers  would  refer  to  it  as  a  clean  culture 
orchard!  Similarly,  if  the  land  were  seeded  down  to  bluegrass  or  alfalfa 
or  some  other  forage  crop,  the  method  of  soil  management  would  be 
classed  as  sod,  sod  mulch  or  intercrop,  depending  upon  what  disposition 
is  made  of  the  vegetation  produced  between  the  trees.  If  the  vegetation 
were  cut  and  removed  from  the  land,  the  orchard  would  be  said  to  be 
under  an  intercrop  system  of  management,  but  if  it  were  pastured  off 
by  sheep  the  management  probably  would  be  called  a  sod  system,  though 

31 


32  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

if  the  vegetation  were  cut  and  allowed  to  remain  on  the  ground  as  a 
mulch  the  treatment  would  be  called  a  sod-mulch  system.  No  attempt 
is  made  here  to  go  into  any  detail  regarding  some  of  these  systems  of 
soil  management  that  are  very  much  alike  or  that  are  intermediate  in 
character  between  those  that  stand  out  clearly  as  types.  However,  it 
is  desirable  to  recognize  how  certain  of  the  typical  systems  of  soil  manage- 
ment may  be  expected  to  influence  the  water  content  of  the  soil  and, 
through  it,  the  growth  and  behavior  of  the  tree.  With  this  information 
at  hand,  it  will  not  be  difficult,  as  a  rule,  to  predict  more  or  less  accurately 
the  results  that  may  be  expected  from  one  of  the  intermediate  or  combi- 
nation treatments. 

Orchard -soil  Management  Methods  and  Surface  Run-off. — A 
word  may  be  said  first  regarding  the  influence  of  these  several  methods 
of  soil  treatment  upon  surface  run-off.  Much  of  course  depends  upon 
the  lay  of  the  land,  the  character  of  the  soil  itself  and  the  way  in  which 
precipitation  occurs.  Most  soils  cannot  take  up  the  water  that  falls 
in  a  torrential  rain  lasting  but  an  hour  so  completely  as  they  can  the  same 
amount  of  rainfall  distributed  over  a  12-  or  24-hour  period.  Exact 
figures  are  not  available,  but  it  has  been  observed  many  times  that  there 
is  much  less  run-off  from  sodded  areas  than  from  equal  areas  of  similarly 
lying  bare  land.  The  covering  of  vegetation  or  of  mulching  material 
checks  the  flow  of  the  water  over  the  surface  of  the  ground  and  gives 
it  a  greater  opportunity  to  soak  in.  Furthermore,  if  there  is  any  con- 
siderable amount  of  mulching  on  the  ground  it  acts  as  a  sponge,  first 
absorbing  the  water  as  it  falls  and  then  permitting  it  slowly  to  seep  into 
the  soil.  In  this  connection,  mention  should  be  made  of  the  influence 
of  mulching  material  or  vegetation  of  any  kind  upon  erosion.  There 
are  many  orchards  and  parts  of  many  others,  planted  on  slopes  so  steep 
that  there  would  be  much  loss  of  soil  from  washing,  were  the  land  to  be 
cultivated  and  left  bare  any  considerable  portion  of  the  year.  Orchards 
of  this  type  should  be  left  in  sod  or  artificially  mulched,  regardless  of 
how  these  treatments  may  influence  the  water  or  nutrient  supply  avail- 
able to  the  trees. 

Moisture  Under  Tillage  and  Sod-mulch  Systems  of  Management. — 
There  is  Httle  reason  to  beheve  that  there  is  much  difference  between 
the  methods  of  soil  management  in  the  amounts  of  seepage  into  the  lower 
layers  of  the  soil.  However,  it  is  obvious  that  these  several  treatments 
would  have  very  different  influences  upon  surface  evaporation  from  the 
soil  and  the  evaporation  that  takes  place  through  the  plant  itself.  Fortu- 
nately, considerable  data  are  available  upon  certain  phases  of  this 
question. 

Some  New  York  and  Pennsylvania  Records. — The  New  York  data 
presented  in  Table  18  show  nearly  5  per  cent,  difference  in  soil  moisture 
between  the  surface  soils  of  the  tilled  and  of  the  sodded  orchards  and 


ORCHARD  SOIL  MANAGEMENT  METHODS 


33 


nearly  4  per  cent,  difference  in  the  respective  subsoils.  When  it  is  con- 
sidered that  a  part  of  the  water  in  each  case  is  unavailable  for  tree  growth 
because  needed  to  supply  the  hygroscopic  requirements  of  the  soil,  it  is 
evident  that  the  tilled  ground  may  contain  many  times  as  much  available 
moisture  as  the  land  in  sod  and  that  the  difference  between  the  two 
methods  of  culture  in  respect  to  the  available  water  is  actually  much 
greater  than  the  figures  would  suggest  at  first  glance,  The  Pennsylvania 
data  presented  in  Table  19  show  clearly  that  artificial  mulching  may  be 
and  indeed  usually  is,  a  most  efficient  means  of  reducing  evaporation. 
They  also  throw  some  light  on  the  effect  of  intercrops  and  cover  crops 
upon  the  water  content  of  the  soil,  though  no  information  is  available  as 
to  the  season  in  which  the  determinations  were  made.  Incidentally, 
Table  19  shows  how  the  soil-water  supply  influences  the  growth  and  the 
yield  of  apple  trees,  though  it  should  not  be  inferred  that  all  the  differences 
in  growth  and  yield  are  due  directly  to  the  variations  in  water  supply. 
It  is  significant,  however,  that  there  is  a  close  correlation  between  the  two. 


Table   18. — Soil-moisture   Determinations  in  a   Mature   Apple   Orchard   in 

New  York^^ 
(Under  different  methods  of  soil  management) 


1907 

1908 

1  to  6 

inches 

6  to  12  inches 

Date 

1  to  6  inches 

6  to  12  inches 

Date 

Till- 
age 

Sod 

Till- 
age 

Sod 

Till- 
age 

Sod 

Till- 
age 

Sod 

6-28 

12.71 

6.23 

12.90 

6.31 

7-  7 

12.77 

11.59 

11.56 

10.70 

7-  2 

14.88 

11.20 

14.86 

6.99 

1       7-10 

12.43 

6.62 

10.89 

6.29 

7-  5 

12.07 

5.87 

10.96 

3.37 

7-14 

12.69 

9.00 

10.58 

6.03 

7-  9 

13.12 

6.96 

12.04 

6.53 

7-22 

18.31 

14.02 

17.76 

9.59 

7-12 

16.43 

13.51 

15.31 

9.26 

7-24 

15.25 

11.85 

16.14 

9.37 

7-16 

13.77 

9.63 

11.75 

8.69 

7-28 

12.40 

10.84 

11.67 

8.25 

7-19 

11.68 

9.51 

9.48 

7.80 

7-31 

15.50 

13.31 

15.56 

10.09 

7-23 

13  42 

8.36 

9.19 

7.80 

8-  4 

14.00 

12.97 

12,84 

10.87 

7-26 

11.93 

6.81 

8.84 

5.21 

8-  7 

15.35 

9.72 

15.31 

7.61 

7-30 

11.69 

5.46 

9.84 

4.72 

8-11 

15.27 

10.08 

15.28 

8.02 

8-  2 

13.20 

7.82 

10.92 

5.75 

8-14 

14.72 

11.70 

12.47 

8.10 

8-  6 

10.64 

7.08 

10.72 

5.47 

8-18 

14.56 

14.07 

12.98 

12.71 

8-  8 

10.02 

4.82 

10.15 

3.80 

8-21 

12.33 

8.70 

11.21 

7.81 

8-14 

11.79 

4.38 

9.62 

4.07 

8-25 

10.98 

6.39 

9.39 

6.08 

8-17 

9.37 
8.56 

5.21 
3.99 

9.07 
8.18 

3.. 58 
2.68 

8-20 

Average    for 
season 

12.20 

7.30 

10.86 

5.75 

14.04 

10.06 

13.12 

8.68 

34 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Table  19. — Influence  of  Cultural  Methods  on  Moisture,  Growth  and  Yield 

IN  a  Young  Orchard 

(Results  from  Experiment  331,  first  7  years,  1908-1914122) 


Treatment 

Moist- 
ure 
content 

1913, 
per 

cent. 

Rela- 
tion to 
optimum 
content, 
per 
cent. 

Average 
gain  in 
girth, 
inches 

Gain 
over 
tillage, 
per 
cent. 

Total 

yield 

1914, 

pounds 

General 
rank 

Tillage 

Tillage  and  intercrop 

Tillage  and  cover  crop.  .  .  . 
Cover  crop  and  manure . .  . 
Cover  crop  and  fertilizer .  . 
Mulch 

10.6 
5.5 

8.5 

9.2 

9.4 

17.1 

18.2 
18.1 

53.0 
27.6 
42.7 
45.9 
47.2 
85.6 
90.8 
90.4 

6.84 
7.69 
6.84 
8.31 
7.76 
8.29 
8.76 
8.93 

12.4 

21.5 
13.5 
21.2 
28.1 
30.5 

1.5 

21.6 

7.0 

135.4 

18.9 

38.5 

300.5 

390.1 

8 
6 
7 
3 
5 
4 

Mulch  and  manure 

Mulch  and  fertilizer 

2 
1 

Some  New  Hampshire  Records. — That  the  moisture  supply  in  a  tilled 
orchard  is  not  invariably  superior  to  that  in  one  under  a  sod-mulch  system 
of  soil  management  is  shown  by  the  data  presented  in  Table  20  from  an 
orchard  on  light  sandy  loam  in  New  Hampshire.  In  this  instance 
measurements  were  taken  of  the  percentage  of  moisture  in  the  surface 
7  to  9  inches  of  soil  and  in  the  subsoil  (to  a  depth  of  3  feet)  at  weekly 
intervals  during  the  growing  periods  of  four  successive  seasons.  The 
figures  represent  seasonal  averages. 

Gourley,  in  reporting  these  observations,  suggests  that  the  lower  moisture 
in  the  tilled  plot  may  be  due  in  part  to  the  greater  permeability  of  the  subsoil 
and  in  part  to  the  absence  of  a  covering  to  shade  the  soil.  Additional  factors 
cited  as  possible  explanations  are  a  slight  mulch  in  the  sod  plot,  the  slight  demand 
made  by  the  poor  grass  and  finally,  the  increased  drain  on  the  soil  in  the  tilled 
plot  due  to  the  larger  growth  and  larger  leaves  on  the  apple  trees  growing  there. 
It  should  be  stated  that  despite  the  higher  moisture  content  in  the  sod  plot  the 
growth  and  yields  there  were  inferior.  Gourley,  discussing  a  late  summer 
drought  accompanied  by  a  severe  dropping  of  fruit,  states,  "The  dropping  was 
just  as  severe  in  the  heavier  soil  which  showed  12  per  cent,  of  moisture  as  in  the 
lighter  soil  which  showed  about  7  per  cent,  which  would  agree  with  the  findings 
of  the  soil  physicists  on  the  wilting  point  in  light  and  heavy  soils." 

English  Experience. — Bedford  and  Pickering^''  report  some  interesting  data 
showing  that  uniform  results  are  not  attendant  upon  similar  treatments.  "Pot 
experiments  under  glass  indicated  that,  during  the  summer  months,  30  per  cent, 
more  water  was  lost  from  the  pots  where  there  was  a  surface  crop  than  from  those 
where  there  was  none;  but  when  the  pots  were  in  the  open,  exposed  to  the  sun 
and  wind,  the  reverse  was  often — not  always — the  case,  and  the  evaporation 
from  the  pots  with  the  surface  crop  might,  during  the  season,  be  even  less  than 
half  of  that  from  those  without  a  surface  crop." 


ORCHARD  SOIL  MANAGEMENT  METHODS 


35 


Table   20. — Moisture   Determinations   on   Sod   Cultivation   and  Cover  Crop 

Plots 

(Light  sandy  loam  in  New  Hampshire) 

(After  Gourleif) 

Surface  soil 


Year 

Sod 

Tillage 

Tillage  and  cover 
crops 

1913 

16.02 

13.69 

14.20 

1914 

18.87 

13.39 

15.03 

1915 

25.63 

19.29 

20.82 

1916 

20.48 

16.45 

21.31 

Average 

20.25 

15.70 

17.84 

Sub 

soil 

Year 

Sod 

Tillage 

Tillage  and  cover 
crops 

1913 

10.98 

9.06 

8.93 

1914 

14.14 

9.78 

10.26 

1915 

14.26 

14.03 

13.33 

1916 

14.82 

12.74 

13.24 

Average 

13.55 

11.40 

11.44 

At  Harpenden  they  found  during  May,  June  and  July  an  average  of  4  per 
cent,  more  moisture  in  tilled  soil  than  in  grass  land;  in  Ridgmont  soil,  grassed 
land  in  August  and  September  contained  on  the  average  0.7  per  cent,  more  water 
than  tilled  land.  In  no  case  did  the  amount  of  moisture  appear  to  be  the  chief 
factoi-  in  tree  growth.  Irrigation  increased  the  vigor  of  fruit  trees  growing  in 
grass  land,  but  did  not  make  them  as  thrifty  as  those  grown  in  tilled  ground. 


The  New  Hampshire  and  the  English  results  agree  in  the  superior 
growth  made  by  trees  in  tilled  ground,  despite  the  absence  of  significant 
differences  in  moisture,  or  indeed,  despite  the  frequent  superiority  of 
grass  land  in  moisture  content.  In  these  cases  there  is  evidence  of  the 
effect  of  other  limiting  factors,  some  of  which  are  discussed  in  the  section 
on  nutrition. 

Special  cases  deserve  passing  consideration.  The  Hitchings  orchard 
in  New  York  showed  under  test  as  good  results  in  growth  and  yield  under 
the  sod-mulch  system  as  under  tillage.^*'     This  condition  is  explained  as 


36  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

the  result  of  seepage  from  the  hill  at  the  bottom  of  which  the  orchard  is 
located,  supplying  so  much  water  that  moisture  is  eliminated  as  a  limiting 
factor.  Many  orchards  in  the  eastern  United  States  are  in  just  such 
locations. 

Some  Kentucky  and  Kansas  Records. — Some  of  the  findings  of  the 
United  States  Bureau  of  Soils  on  soil  moisture  conditions  in  grass  land 
and  in  cultivated  soil  may  be  summarized  here.  Records  were  made 
during  the  months  of  May,  June  and  July,  1895,  of  the  water  content  of 
soils  at  a  number  of  places  in  the  United  States  and  under  different 
tillage  conditions.^-^  These  records  bring  out  a  great  difference  between 
soils  in  the  way  this  moisture  content  is  influenced  by  treatment.  For 
instance,  at  Greendale,  Ky.,  during  the  last  half  of  May,  the  moisture 
contents  of  uncultivated,  bare  land  and  of  bluegrass  sod  were  pract- 
ically the  same  (about  18  per  cent.) ;  during  June,  however,  the  moisture 
content  under  the  bluegrass  gradually  decreased  to  about  10  per  cent, 
while  that  of  the  uncultivated  bare  land  remained  about  17  per  cent, 
except  for  a  period  of  about  5  days  at  the  end  of  the  month  when  it 
dropped  practically  to  the  figure  shown  by  the  sod  land.  During  July 
the  bare,  uncultivated  land  averaged  2  to  3  per  cent,  higher  in  moisture 
content  than  the  grass  land.  At  Lexington,  Ky.,  a  similar  series  of 
records  showed  an  average  moisture  content  about  5  per  cent,  higher  dur- 
ing May,  8  to  10  per  cent,  during  June,  and  1  to  5  per  cent,  during  July, 
in  the  bare,  uncultivated  land  compared  with  that  under  bluegrass  sod. 
During  June  the  bluegrass  made  its  very  heavy  draft  upon  the  moisture 
supply  of  the  soil,  lowering  it  to  the  point  where  little  water  was  available 
for  plant  growth  and  cultivated  crops  consequently  suffered. 

This  suggests  that  if  the  sod-mulch  system  of  orchard  culture  checks 
tree  growth  materially  during  the  early  part  of  the  season  or  again  after 
mid-season  it  is  not  on  account  of  its  lowering  the  water  content  of  the 
soil,  at  least  in  those  sections  favored  with  summer  rains.  On  the  other 
hand,  orchards  in  sections  likely  to  have  little  rain  between  the  middle 
of  June  and  early  fall  probably  would  suffer  materially  from  drought  during 
that  period.  In  any  case,  the  growth  of  grass  mulching  material  would 
take  large  amounts  of  water  during  June;  during  that  month  the  itrees, 
may  or  may  not  be  able  to  spare  it.  The  question  of  the  practicablity, 
desirability  or  efficiency  of  the  grass  mulch  method  of  culture  so  far  as  it 
concerns  soil  moisture  therefore  depends  on  what  precipitation  can  be 
expected  reasonably  during  July,  August  and  September  or  what  can  be 
applied  by  irrigation — for  orchards  under  these  two  methods  of  soil 
management  are  very  likely  to  enter  this  period  with  material  differences 
in  the  amount  of  available  soil  moisture.  In  Scott,  Kan.,  on  the  other 
hand,  the  moisture  content  of  prairie  sod  land  has  been  found  to  average 
only  about  8  per  cent,  during  the  last  half  of  May,  while  cultivated  land 
averaged  about  17  per  cent.     Rains  late  in  May  and  scattered  through 


ORCHARD  SOIL  MANAGEMENT  METHODS  37 

June  and  July,  brought  up  the  averages  in  both  soils  to  well  above  the 
danger  point  for  plant  growth  and  the  cultivated  soil  averaged  only  2  to 
5  per  cent,  more  moisture  during  those  months. 

In  General. — That  the  sod-mulch,  or  any  other  sod  method  of  manage- 
ment, makes  something  of  a  draft  upon  the  water  supply  of  the  soil,  as 
compared  with  a  tillage  method  of  management,  cannot  be  denied,  though 
this  draft  is  often  less  than  is  supposed.  It  would  be  a  very  good  sod- 
mulch  indeed  that, would  produce  1  dry-weight  ton  of  mulching  material 
per  acre.  More  frequently  the  amount  does  not  exceed  half  that  figure. 
One-half  ton  of  dry  mulching  material  would  require  from  31,250  to 
62,500  gallons  of  water,  assuming  from  250  to  500  parts  of  water  for  each 
part  of  drj--  matter.  This  would  be  the  equivalent  of  13^  to  2}^  acre-inches 
of  rainfall  or  irrigation.  Furthermore,  most  of  this  water  is  used  by  the 
grass  during  the  months  of  April,  May  and  June,  when  the  soil  is  most 
likely  to  be  well  supplied  with  moisture  and  best  able  to  part  with  it.  If 
the  growing  season  of  the  grass  is  followed  by  moderate  or  heavy  summer 
rains  or  irrigation  the  requirements  of  the  trees  will  be  well  taken  care  of 
in  this  respect.  On  the  other  hand,  if  there  should  follow  a  period  of 
drought,  it  is  easy  to  understand  why  trees  under  sod  treatment  would 
suffer.  An  important  factor,  then,  in  determining  the  practicability  of  the 
sod-mulch  method  of  management  is  the  likelihood  or  certainty  of  summer 
precipitation,  or,  what  amounts  to  the  same  thing,  available  irrigation 
supply  during  the  summer  months.  In  sections  such  as  the  Willamette 
valley  of  Oregon  where  winter  and  spring  rains  are  abundant  but  the 
summer  is  dry,  the  sod-mulch  method  of  management  cannot  be  employed 
safely  without  irrigation.  In  such  regions  it  is  wise  to  use  every  means 
of  conserving  the  natural  water  supply.  On  the  other  hand,  there  are 
many  sections  and  many  locations  where  summer  rains  can  be  counted 
on  to  supply  the  requirements  of  the  trees  during  their  growing  season 
year  after  year;  in  other  cases  an  orchard  may  be  so  located  in  a  valley 
floor  or  a  piece  of  bench  land  that  it  is  sub-irrigated  by  means  of  seepage 
water.  Under  these  conditions  the  sod-mulch  method  of  management  is 
entirely  practicable,  though  it  should  be  stated  that  such  orchards  may 
need  somewhat  different  treatment,  so  far  as  nutrition  is  concerned,  than 
orchards  in  cultivation.  A  study  of  the  records  of  the  United  States 
Weather  Bureau  showing  monthly  precipitation  over  a  series  of  years 
will  give  important  data  as  to  the  relative  desirability  or  practicability 
of  these  several  methods  of  soil  management  for  any  particular  region 
or  district. 

Sometimes  the  choice  of  methods  is  influenced  by  considerations 
of  the  cost  of  the  systems.  Hedrick^"*  reports  that  the  operations 
involved  in  the  sod-mulch  and  tillage  systems  cost  per  acre  respectively: 
for  the  Auchter  orchard  80  cents  and  $7.39,  for  the  Hitchings  orchard 
72  cents  and  $16.28.     In  many  cases  the  tillage  method  will  more  than 


38  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

return  the  extra  labor  cost;  however,  when  results  are  equal,  costs  should 
be  considered. 

Practicability  of  the  Sod-mulch  System  Influenced  by  Depth  of  Rooting. — 
Mention  of  depth  of  rooting,  a  subject  considered  in  more  detail  later, 
is  pertinent  to  this  discussion.  A  tree  with  a  root  system  penetrating 
the  soil  to  a  depth  of  8  or  10  feet  can  draw  upon  the  moisture  supply  of  a 
large  volume  of  soil.  Such  a  tree  is  in  a  much  better  position  to  with- 
stand temporary  surface  drying  such  as  may  be  produced  by  evaporation 
from  the  surface  or  from  weeds  and  grass,  than  a  tree  whose  roots  are 
limited  to  the  upper  foot  or  eighteen  inches  of  soil.  Consequently 
it  will  thrive  under  the  sod-mulch  method  of  culture  when  a  shallow- 
rooted  tree  would  suffer  serious  injury.  To  keep  an  orchard  in  sod  under 
conditions  such  that  deep  rooting  is  not  possible  and  where  there  is  not 
an  abundant  summer  rainfall  or  plenty  of  irrigation  water,  is  to  invite 
trouble.  However,  there  are  successful  orchards  in  sod  where  the 
summers  are  long  and  dry  and  irrigation  is  not  known.  The  explanation 
lies  in  the  deep  root  system  of  the  trees  that  makes  them  independent, 
to  a  great  degree,  of  surface  soil  conditions. 

In  passing  it  should  be  mentioned  that  the  grass,  both  cut  and  uncut, 
of  the  sod  systems  of  management  affords  some  protection  against  surface 
evaporation,  the  exact  degree  depending  on  the  thickness  of  the  protective 
layer.  As  this  layer  is  frequently  rather  thin,  its  importance  in  checking 
evaporation  is  often  exaggerated,  for  the  stubble  of  the  cut  grass  continues 
to  evaporate  moisture  into  the  air,  even  after  it  has  turned  brown  and  has 
died  down  to  the  ground.  In  some  cases  this  water-dissipating  action 
of  the  stubble  during  the  summer  months  may  even  equal  the  protective 
action  of  the  mulch  against  evaporation. 

Influence  of  Depth  and  Frequency  of  Cultivation  Upon  Soil  Moisture. 
Since  cultivation  is  in  general  a  means  of  conserving  soil  moisture, 
the  presumption  is  that  the  deeper  the  cultivation,  within  reasonable 
limits,  the  more  effective  it  will  be.  Table  21  affords  a  fairly  accurate 
idea  of  how  depth  of  soil  mulch  influences  the  loss  of  water  by  evaporation. 
It  is  worthy  of  note  that  with  a  soil  mulch  6  inches  deep  the  water  lost 
by  evaporation  is  less  than  a  quarter  of  that  lost  through  a  1-inch  mulch. 
Regardless  of  the  texture  of  the  soil,  cultivation  is  equally  effective  as  a 
protection  against  water  loss :  this  protective  influence  is  felt  to  a  depth 
of  6  feet. 

Table  21  is  interesting  also  because  it  shows  the  combined  effects  of 
depth  and  frequency  of  cultivation.  It  is  evident  that  increasing  the 
frequency  of  the  cultivations,  at  least  up  to  a  certain  point,  increased  the 
effectiveness  of  the  soil  mulch  under  the  conditions  of  the  experiment. 
Probably  under  arid  or  semiarid  conditions  with  few  or  no  summer  rains 
and  less  weed  growth  the  more  intensive  tillage  would  not  give  materially 
increased  protection  against  evaporation. 


ORCHARD  SOIL  MANAGEMENT  METHODS 


39 


Table  21.- 


-The  Relative  Effectiveness  of  Soil  Mulches  of  Different  Depths 
AND  Different  Frequencies  of  Cultivation^* 


Depth 

Loss  of  water  per  acre 
per  100  days 

Cultivation 

of  soil 
mulch, 
inches 

None 

Once  in 
2  weeks 

Once  per 
week 

Twice  per 
week 

1 

Tons                

724.1 
6.394 

724.1 
6.394 

724.1 
6.394 

551.2 
4.867 
23.88 

609.2 
5.380 
15.88 

612.0 
5.402 
15.49 

545.0 
4.812 
24.73 

552.1 
4.875 
23.76 

531.5 
4.694 
26.60 

527.8 

4.662 

2 

Water  saved,  per  cent 

Tons              

27.10 
515.4 

4.552 

3 

Water  saved,  per  cent 

Tons                

28.81 
495.0 

4.371 

Water  saved,  per  cent 

31.64 

Intercrops  and  the  Soil  Moisture  Supply. — The  influence  of  various 
intercrops  upon  soil  moisture  conditions  in  the  young  orchard  has  been 
studied  by  Emerson.*^  Results  of  these  studies,  covering  two  successive 
seasons,  1901  and  1902,  are  presented  graphically  in  Fig.  1.  These  two 
seasons  afforded  more  or  less  extreme  conditions  of  precipitation.  The 
summer  of  1901  was  characterized  by  very  light  rainfall,  so  light  in  fact 
that  the  trees  would  have  to  depend  largely  upon  stored  moisture  during 
the  period  of  their  most  active  growth.  On  the  other  hand,  the  summer 
of  1902  was  a  season  of  abundant  rainfall.  The  crops  grown  in  the 
vegetable  plot  included  water  melons,  bush  beans,  pole  beans  and  turnips. 

In  commenting  upon  the  results  of  this  investigation  Emerson  says: 
"The  vegetables  dried  the  soil  but  little  more  than  clean  cultivation.  In 
neither  case  did  the  percentage  of  moisture  become  dangerously  low,  even  during 
the  protracted  drought  of  1901,  when  only  a  little  over  7  inches  of  rain  fell  during 
the  4  months  from  May  to  August  inclusive.  The  crops  of  rye  dried  the  ground 
much  more  than  any  other  method  of  culture  tried.  Not  only  was  the  rye  ground 
somewhat  drier,  but  it  became  dry  earlier,  and  moreover,  since  no  rains  occurred 
to  thoroughly  moisten  the  ground  after  it  had  once  become  dry,  the  rye  plot 
remained  dry  nearly  a  month  longer  than  any  of  the  other  plots.  Next  to  rye, 
the  oat  crop  dried  the  soil  most  seriously  during  the  dry  season  of  1910,  though  it 
did  not  make  the  soil  much  drier  than  corn  or  cover  crops.  Its  effect,  however, 
was  noticeable  much  earlier  in  summer  and  lasted  much  longer.  By  the  middle 
of  July,  when  the  corn  plot  was  becoming  dry,  many  trees  have  completed  their 
greatest  length  growth  and  do  not  need  so  large  a  supply  of  moisture  as  they  do 
earlier  in  the  season.  The  corn  plot  was  very  dry,  therefore,  only  about  half  as 
long  as  the  oats  plot.  The  important  difference  between  the  cover  crop  and  the 
corn,  just  as  between  the  corn  and  the  oats,  is  that  the  soil  in  the  cover  crop  plot 


40 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


did  not  become  dry  for  a  week  or  two  after  the  corn  ground  had  become  dry. 
The  great  difference,  as  regards  soil  moisture  between  the  clean  cultivation 
on  the  one  hand  and  the  rye  and  oats  on  the  other  is  fully  appreciated  only  when 
it  is  remembered  that  the  moisture  in  excess  of  8  or  10  per  cent,  (in  this  particular 
soil)  is  available  to  plants.  .    .    ,     In  1902,  the  plots  did  not  vary  greatly  as  regards 


Apnl_ 


o0.5 


_May_ 


June 


1901 


Aug.        Sept. 


Oct. 


^ 

^ 

\ 

^ 

^ 

% 

1 

c 

Sl< 

-/^ 

m 

.\ 

-c            \ 

^ 

'^ 

Jf 

\ 

\ 

_^ 

1 

\ 

V 

/\ 

■f~^ 

J 

"^^^--^ 

1 

III 

il       1 

h 

1 

II 

1 

1 

Fig.  1. — Percentages  of  soil  moisture  in  orchard  plots  and  inches  of  rainfall  during 
summers  of  1901  and  1902.  The  curved  lines  indicate  the  fluctuations  in  soil  moisture 
content.     The  vertical  bars  show  dates  and  amounts  of  rainfall.     (After  Emerson.*^) 


soil  moisture.  Naturally,  no  method  of  culture  dried  the  ground  seriously  at 
any  time  during  this  very  wet  season,  when  over  28  inches  of  rain  fell  during  the 
4  months  from  May  to  August  inclusive."^* 

Table  22  presents  data  showing  the  effects  of  the  various  intercrops 
in  this  Nebraska  experiment  upon  the  drought  killing  of  newly  set  trees. 


ORCHARD  SOIL  MANAGEMENT  METHODS 


41 


Table   22. — Effect   of  Various   Intercrops   on   Drought   Killing  of  Young 

Trees  (After  Emerson^^) 


Apple 

Cherry 

Peach 

Intercrop 

Num- 

Num- 

Per 

Num- 

Num- 

Per 

Num- 

Num- 

Per 

ber 

ber 

cent. 

ber 

ber 

cent. 

ber 

ber 

cent. 

set 

died 

died 

set 

died 

died 

set 

died 

died 

Watermelon  crop 

30 

2 

7 

12 

1 

9 

10 

0 

0 

Watermelon  crop 

30 

2 

7 

12 

2 

17 

10 

0 

0 

Corn  crop 

30 

2 

7 

12 

1 

9 

10 

2 

20 

Clean  cultivation 

30 

3 

12 

0 

0 

10 

0 

0 

Oats  crop 

30 

14 

47 

12 

6 

50 

10 

8 

80 

Cover  crop,  millet 

30 

13 

12 

2 

17 

10 

1 

10 

Cover  crop,  oats 

30 

13 

12 

4 

33 

10 

0 

0 

Cover  crop,  weeds 

30 

23 

12 

6 

50 

10 

0 

0 

Table    22. — Continued 


Intercrop 


Num- 

Num- 

Per 

ber 

ber 

cent. 

set 

died 

died 

,„ 

0 

0 

10 

2 

20 

10 

2 

20 

10 

1 

10 

10 

6 

60 

10 

2 

20 

10 

1 

10 

10 

0 

0 

Plum 

Total 

Num- 

Num- 

Per 

Num- 

Num- 

ber 

ber 

cent. 

ber 

ber 

set 

died 

died 

set 

died 

cent, 
died 


Watermelon  crop. 
Watermelon  crop. 

Corn  crop 

Clean  cultivation. 

Oats  crop 

Cover  crop,  millet 
Cover  crop,  oats.  . 
Cover  crop,  weeds 


1 

7 

76 

4 

0 

0 

76 

6 

0 

0 

76 

7 

0 

0 

76 

2 

5 

36 

76 

39 

0 

0 

76 

9 

1 

7 

76 

10 

2 

14 

76 

15 

5.4 
7.9 
9.2 
2.6 
51.3 
11.8 
12.2 
19.7 


The  data  for  the  cover  crops  indicate  relatively  more  injury  than  would 
occur  in  older  orchards  because  the  cover  crops  probably  made  a  much 
more  vigorous  growth  than  they  would  in  competition  with  well  estab- 
lished trees.  The  suggestion  is  made,  however,  that  cover  crops  should 
be  selected  and  used  with  considerable  care  in  recently  established 
orchards.  The  danger  from  the  use  of  the  small  grains  as  orchard  inter- 
crops is  indicated  plainly.  On  the  other  hand,  little  loss  is  occasioned 
by  the  growing  of  tilled  or  hoed  intercrops. 

Cover  Crops  and  the  Moisture  Supply. — Orchard  cover  crops  are  not 
generally  considered  in  relation  to  soil  moisture,  but  rather  as  means  of 
adding  organic  matter  to  the  soil  and  increasing  productivity.  Never- 
theless they  do  influence  water  content  in  several  ways  and  some  data  on 
this  question  have  already  been  presented  in  connection  with  the  discus- 
sion of  intercrops.  As  this  influence  is,  in  many  cases,  important  it  seems 
desirable  that  further  consideration  be  given  the  matter. 


42 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Effects  of  Early  and  Late  Seeding. — Cover  crops  use  considerable 
water  in  their  growth.  A  good  cover  crop  probably  produces  at  least 
14,  ton  of  dry  matter  per  acre  involving  the  transpiration  of  from  2  to  4 
acre-inches  of  water.  However,  the  cover  crop  makes  its  demand  for 
water  upon  the  soil  during  the  fall,  winter  and  spring  months — a  time 
when  there  is  most  likelihood  of  an  abundant  water  supply  and  conse- 
quently when  the  trees  are  not  so  likely  to  be  injured  by  the  draft  of  the 
cover  crops.  It  is  true  that  cover  crops  are  usually  seeded  in  late  July  or 
in  August,  but  their  growth  is  so  limited  before  the  middle  or  end  of 
September  that  they  compete  but  little  with  the  trees  for  either  nutrients 


Table  23.- 


-Percentage  of  Soil  Moisture  in  Bare  Ground  and  Under  Cover 
Crops  in  Early  November  After  a  Drought^s 


Depth  in  inches 

Bare  ground 

Hairy  vetch 

Cowpea 

1 
1  to  12                            6 .  48 
12  to  18             1               8.52 
18  to  24             ,               7.60 

1 
12.15.                             9.30 
10.30                            12.27 
11.65                                9.80 

Table  24. — Percentage  of  Soil  Moisture  for  Each  Cover  Crop  from  Nov.  1, 
1905,  to  Feb.  17,  1906,  and  the  Average  for  Three  Determinations" 


Crop 


Percentage  of  moisture  in  soil  to  depth  of  30  inches 


Nov. 
21-22,  1905 


Jan. 
2-3,  1906 


Feb. 
16-17,  1906 


Average 


Cowpeas 

Soy  beans 

Crimson  clover 

Hairy  vetch 

Oats 

Canada  peas 

Oats  and  Canada  peas 

Rye 

Check 

Millet 

Rape 

Turnip 

Turnip  and  rye 

Hairy    vetch    and    Canada 

peas 

Oats  and  crimson  clover.  .  . 
Cowpeas  and  crimson  clover 

Average 


17.7 
18.9 
18.6 
17.4 
17.0 
17.7 


17.3 
17.6 
18.1 

17.1 


24.5 
23.2 
23.7 
24.6 
22.7 
21.4 
25.5 
22.5 
22.4 
23.4 
24.0 


23.5 


21.9 
23.4 
23.4 
20.5 
21.2 
18.8 
22.0 
21.7 
20.4 
20.6 
21.7 
19.3 
22.5 

19.2 
20.0 
26.7 

21.5 


21.7 
21.9 
21.9 
20.8 
20.3 
19.3 
21.1 
20.2 
19.7 
20.0 
20.7 


20.7 


ORCHARD  SOIL  MANAGEMENT  METHODS  43 

or  water.  Furthermore,  the  protective  action  of  the  cover  crop  through 
checking  wind  velocity  close  to  the  ground  and  through  shading  the  soil, 
thus  lowering  its  temperature,  may  fully  compensate  for  its  use  of  water 
during  the  late  smnmer  and  early  fall.  The  data  presented  in  Tables  23 
and  24  show  that  later  in  the  season,  cover  crops  may  actually  contribute 
indii-ectly  to  the  soil  moisture  content.  The  examinations  recorded  in 
Table  23  were  made  at  Ithaca,  N.  Y.,  in  November  1901,  at  the  close  of  an 
extended  drought.  Those  recorded  in  Table  24  were  made  at  intervals 
during  the  winter  of  1905-1906  in  Wisconsin.  The  report  upon  this 
latter  investigation  states  that  the  moisture  determinations  taken  in  the 
spring  on  the  soil  under  these  cover  crops  confirms  the  results  obtained 
in  the  fall  and  winter  "in  that  it  shows  the  average  moisture  content  of  the 
covered  ground  to  be  considerably  more  than  that  of  the  bare  ground."*^ 
There  are  distinct  differences  between  various  cover  crops  in  their  influ- 
ence upon  the  water  content  of  the  soil. 

However,  if  cover  crops  are  started  so  early  in  the  season  that  a 
considerable  amount  of  growth  is  made  during  July  and  August,  or  even 
early  September,  they  are  likely  to  make  serious  drafts  upon  the  water 
supply  of  the  surface  soil,  which  might  check  the  vegetative  growth  of  the 
trees  prematurely  and  reduce  the  size  of  the  fruit.  Striking  evidence  on 
this  point  is  furnished  by  an  experiment  in  which  cylindrical  cans  were 
filled  with  heavy  soil  from  an  orange  grove. ^^  One  was  left  undisturbed 
as  a  check,  in  one  a  surface  soil  mulch  was  maintained  and  one  was  seeded 
to  barle^^  The  experiment  was  started  June  25,  at  which  time  the  soil 
contained  19.2  per  cent,  moisture.  At  the  end  of  38  days  the  soil  in  the 
check  cyhnder  contained  10.1  per  cent.,  the  mulched  soil  14  per  cent,  and 
the  soil  seeded  to  barley  3.1  per  cent,  moisture.  The  soil  seeded  to  barley 
had  reached  its  wilting  coefficient  21  days  after  seeding. 

In  certain  cultural  experiments  in  Pennsylvania  the  beneficial  effects 
of  cover  crops  expressed  in  vegetative  growth  and  yield  have  been  most 
apparent  during  the  moist  seasons,  and  little  or  no  benefit  has  been 
derived  from  their  use  during  dry  years. ^^s  ^p^g  rapid  drying  effect  of 
oats,  when  used  as  a  cover  crop  for  peaches  in  Delaware,  has  prevented 
"the  best  growth  of  new  wood  to  produce  the  maximum  number  of  fruit 
buds."^^  The  rate  of  growth  of  cover  crops  as  the  season  advances  is  an 
important  factor  in  determining  their  draft  upon  the  water  supply  of  the 
soil  from  week  to  week.  From  this  point  of  view,  the  ideal  cover  crop  is 
one  which  grows  slowly  at  first  but  rapidly  late  in  the  season  when  the 
trees  do  not  require  so  much  moisture  and  when  the  supply  is  more 
abundant.  Figures  on  the  rates  of  growth,  under  Wisconsin  conditions, 
of  some  of  the  more  common  crops  of  the  Northern  states  are  given  in 
Table  25.  The  indirect  influence  of  cover  crops  upon  soil  moisture  in 
adding  organic  matter  to  the  soil  and  thereby  increasing  its  water-holding 
capacity  is  more  difficult  to  estimate  accurately,  but  there  is  reason  to 


44 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


believe  that  its  importance  in  that  connection  has  been  overemphasized 
often. 

Table  25. — Rate  of  Growth  of  Different  Crops  from  Aug.  25  to  Oct.  2" 
(Height  in  inches) 


Aug.  25 


Sept.  3 


Sept.  15 


Sept.  23         Oct.  2 


Cowpeas 

Soy  beans 

Crimson  clover 
Hairy  vetch .  .  . 

Oats 

Canada  peas.  . 

Rye 

Rape 

Turnip 

Millet 


3.0 


10.0 
8.0 
3.0 
4.5 

11.0 
8.0 
8.0 
4.0 
4.0 
5.0 


12.0 
13.0 

3.5 

5.0 
16.0 
13.0 

9.0 
10.0 

7.0 
11.0 


14.0 

14.5 

4.0 

5.5 

18.0 

20.0 

10.0 

14.0 

8.0 

12.0 


20.0 
22.0 
6.0 
8.0 
24.0 
24.0 
12.0 
16.0 
12.0 
18.0 


Winter-killed  and  Winter-surviving  Cover  Crops. — Cover  crops  are 
generally  classed  as  leguminous  and  non-leguminous  when  considered 
in  relation  to  their  influence  upon  soil  productivity.  Emerson  suggests 
that  when  they  are  being  considered  as  they  influence  soil  moisture  a 
better  classification  would  be  winter-killed  and  winter-surviving.**'  The 
degree  of  cold  actually  experienced  in  a  particular  section  determines 
whether  a  given  crop  is  killed  by  or  survives  the  winter.  Hence,  a  crop 
that  belongs  in  the  one  class  in  one  place  may  fall  in  the  other  in  some 
other  section.  Any  cover  crop  that  survives  the  winter  and  resumes 
active  growth  draws  upon  the  moisture  supply  of  the  soil  in  the  spring 
and  will  continue  to  do  so  until  plowed  under  or  until  cultivation  of  some 
kind  is  begun.  Since  it  is  generally  considered  inadvisable  to -plow  or 
cultivate  deeply  while  trees  are  in  bloom  or  the  fruit  is  setting  and  since 
soil  moisture  conditions  and  the  press  of  other  work  often  make  the 
plowing  of  the  orchard  before  blossoming  impracticable,  cultivation  is  of  ten 
not  begun  until  late  in  May  or  early  in  June.  This  gives  a  winter-sur-' 
viving  cover  crop  an  opportunity  to  make  considerable  growth  in  the 
spring,  often  more  than  it  was  able  to  make  the  previous  fall.  The 
general  effect  of  this  growth  upon  soil  moisture  is  shown  by  the  figures  in 
Table  26  and  is  presented  graphically  in  Fig.  2.  By  June  3  the  winter- 
surviving  cover  crop  had  reduced  the  soil  moisture  to  approximately 
half  the  amount  in  the  soil  protected  by  a  winter-killed  crop.  In  fact  it 
had  consumed  practically  all  the  available  moisture,  leaving  the  water 
content  of  the  soil  but  Httle  above  its  wilting  coefficient.  In  regions  of 
comparatively  high  rainfall  during  the  spring  months,  this  waiter  loss  due 
to  the  growth  of  winter-surviving  cover  crops  would  be  of  secondary 
importance   and    it    would   likewise    be    unimportant  in  sections  with 


ORCHARD  SOIL  MANAGEMENT  METHODS 


45 


Table 


-Effect  of  Various  Cover  Crops  on  Soil  Moisture  During  the 
Spring  of  1901 « 


Kind  of  crop 


Percentage  of  soil  moisture 


Apr.  19         Apr.  27        May  20         June  3 


Winter-killed  crops: 

Oats 

Millet 

Cane 


Average 

Winter-surviving  crops: 
Rve 


28.7 
26.0 
24.0 

26.2 

22.  G 


20.2 
21.8 
22.1 

21.4 

17.4 


20.5 
21.9 
21.7 

21.4 

12.2 


20.1 
20.7 
20.7 

20.5 

11  2 


abundant    and    cheap    irrigation    water,    but   in 

those  seasons  with  a  light  late  spring  and  ^7 

summer   rainfall   it  could   easily   occasion  26 

much  more  financial  loss  than  would  be  is 

compensated  by  the  advantages  accruing  ^4 

from  the  use  of  the  cover  crops.     A  certain  ?3 

quantity  of  organic  material  produced  in  ?2 

the    autumn    is    just    as   valuable   for  soil  '21 

improvement  purposes  as  an  equal  amount  eo 

grown  in  the  spring.  c  19 

Wind  Velocity  and  Evaporation  :  Wind-  ^  18 

breaks. — Attention  has  been  called  to  the  ^^  n 

almost  continual  evaporation  of  water  from  16 

the   soil.     In   regions  of  low  precipitation  15 

this  amounts  to  a  much  larger  percentage  i4 

of   the  total  supply  than  in  regions  of  fre-  i3 

quent     and     abundant    rains.     Assuming  12 

uniform  soil  management  methods,  evap-  >i 

oration  may  be  expected  to   rise  with  an  'O 
increase    in    wind    velocity    and    to   vary 
with  temperature  of  the  soil  water,  with 
temperature  of  the  air  close  to  the  evapo- 
rating surface,  with  vapor  pressure  in.  the 


those   sections 


5 

)l5     - 

\^ 

f^=I 

\^ 

X 

fe 

\' 

1^ 

< 

^ 

% 

Vi 
V^ 

V. 

April 


June 


May 

1901 

Fig.    2.  —  Percentages    of    soil 

moisture    in   plots  of  winter-killed 

and  winter-surviving    cover   crops, 

spring  of  1901.     The  dots  show  the 

.  .      dates   of   making  the  moisture  de- 

air  near  the  water  and  with  atmospheric  terminations  and  the  exact  percent- 
humidity.      The    Onlv  one  of    these  factors  ages  of  moisture  found.    The  curved 
ill"                  1      ,.    1  "'^^^  indicate  the  probable  fluctua- 
at  present  under  the  control  of  the  grower  tions    in    moisture    between   these 

to  any  considerable  extent  is  wind  velocity,  ^^t^^-    (^-^'«''  Emerso7i.''^) 
Consequently  it  is  discussed  at  this  time.     In  one  series  of  determinations 
when  the  relative  humidity  was  50  per  cent,  and  the  air  temperature  84°F. 
evaporation  was  found  to  be  2.2  times  as  rapid  with  a  wind  velocity  of  5 


46  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

miles  per  hour  as  in  a  calm  atmosphere;  3.8,  at  10  miles  per  hour;  4,9,  at  15 
miles  per  hour;  5.7  at  20  miles  per  hour;  6.1,  at  25  miles  per  hour  and  6.3 
at  30  miles  per  hour.^"^  The  influence  of  windbreaks  upon  wind  velocity 
varies  with  their  height  and  density  and  much  depends  also  on  the  topog- 
raphy, Card^^  measured  the  evaporation  in  Nebraska  at  varying 
distances  from  the  protected  side  of  a  windbreak  of  forest  trees  some  30 
feet  high,  during  the  period  July  15  to  Sept.  15,  and  for  those  portions  of 
the  period  when  the  wind  was  from  the  south,  southeast  and  southwest, 
these  being  the  most  drying  winds.  Expressing  the  evaporation  at  a 
point  300  feet  south  of  the  windbreak  as  100,  evaporation  200  feet  north 
was  83  and  50  feet  north,  55.  During  a  12-hour  period  on  Aug.  3,  when 
the  weather  was  hot  and  dry  with  a  high  wind,  evaporation  50  feet  north 
of  the  windbreak  was  29  and  200  feet  north  it  was  67,  compared  with  100 
at  a  point  300  feet  south.  It  is  thus  evident  that  wind  barriers  of  one 
kind  or  another  reduce  evaporation  very  materially.  However,  the 
moisture  required  for  the  growth  of  the  windbreak  materially  reduces 
their  total  moisture-conserving  effect,  though  deep  plowing  or  subsoiling 
close  to  the  windbreak  reduces  its  injurious  influence  in  this  direction. 

Summary. — There  are  six  fairly  distinct  methods  of  soil  management 
commonly  used  in  the  deciduous  fruit  plantation:  (1)  clean  cultivation, 
(2)  clean  culture  with  cover  crop,  (3)  artificial  mulch,  (4)  sod  mulch, 
(5)  sod,  (6)  intercropping.  The  sod  and  sod-mulch  systems  are  most 
effective  in  reducing  run-off  and  in  preventing  erosion;  in  certain  situa- 
tions their  use  is  to  be  recommended  for  these  reasons  if  for  no  other. 
The  various  systems  of  soil  management  employing  tillage  generally 
conserve  a  larger  percentage  of  the  water  that  enters  the  soil  and  conse- 
quently they  are  more  effective  in  preventing  injury  from  drought.  The 
sod-mulch  method  has  its  place  where  abundant  summer  rainfall,  deep 
rooting  or  availability  of  irrigation  water  largely  removes  the  trees  from 
competition  with  the  surface  cultures  for  water.  The  moisture-conserv- 
ing effects  of  tillage  increase  somewhat  with  its  frequency  and  depth,  but 
when  cost  is  considered  there  is  a  decreasing  margin  of  profit  with  the 
deeper  and  more  frequent  cultivation.  Cultivated  intercrops  may  be 
used  safely  in  the  orchard,  but  the  small  grains  are  apt  to  make  too  serious 
a  draft  on  moisture  at  a  period  when  the  trees  should  be  abundantly 
supplied.  Cover  crops  consume  considerable  moisture  but  unless  planted 
too  early  they  are  not  likely  to  injure  the  trees  seriously  by  their  growth 
in  the  fall.  In  fact  they  may  actually  conserve  moisture  for  the  trees 
by  cutting  down  surface  evaporation  and  holding  snow.  In  some  sections 
winter-surviving  cover  crops  should  not  be  used  because  of  their  draft  the 
on  moisture  supply  in  the  spring  when  the  trees  require  it.  This  is  partic- 
ularly true  in  sections  with  only  moderate  rainfall  and  long  dry  summers. 
Evaporation  increases  rapidly  with  wind  velocity  and  moisture  losses 
from  this  cause  can  be  lessened  materially  in  many  cases  by  choice  of 
sites  and  use  of  windbreaks. 


CHAPTER  IV 

SOIL  MOISTURE:  ITS  CLASSIFICATION,  MOVEMENT 
AND  INFLUENCE  ON  ROOT  DISTRIBUTION 

Within  certain  limits  tiie  size  and  general  character  of  top  growth  is 
influenced  bj^  the  root  system  that  supports  it.  Similarly  the  size  and 
distribution  of  the  root  system  depends  to  an  important  degree  on  the 
moisture  content  of  the  soil. 

CLASSIFICATION  OF  THE  WATER  IN  SOILS  AND  PLANT  TISSUES 

The  physicist  finds  it  desirable  to  distinguish  between  water  in  the 
solid,  liquid  and  vapor  form;  the  chemist  distinguishes  between  free 
water,  water  of  crystallization  and  water  of  constitution.  Similarly  it  is 
convenient  for  the  student  of  soils  and  plant  physiology  to  classify  water 
according  to  the  form  in  which  it  is  held  in  the  soil  or  in  plant  tissue  and 
the  consequent  uses  to  which  it  may  be  put.  No  one  classification  has 
proven  most  satisfactory  for  all  purposes.  Attention  is  here  directed  to 
those  that  seem  more  useful  in  explaining  the  response  of  the  plant  to 
varying  water  content. 

The  Response  of  Water  to  the  Force  of  Gravity  and  the  Evaporating 
Power  of  the  Air. — The  water  of  the  soil  is  held  in  three  conditions;  (1)  free, 
or  gravitational  water,  (2)  capillary  water  and  (3)  hygroscopic  water.  The 
free  or  gravitational  water  is  that  which  moves  down  through  the  soil 
under  the  influence  of  gravity.  It  is  the  surplus  water  that  drains  away 
after  heavy  rains  or  heavy  irrigation,  finding  its  way  eventually  through 
underground  channels  to  streams  or  springs  or  to  the  so-called  ground- 
water level.  Capillary  water,  on  the  other  hand,  does  not  move  down- 
ward in  response  to  the  force  of  gravity,  but  adheres  to  the  soil  particles 
in  the  form  of  films  of  varying  thicknesses.  It  does  not  drain  away  freely 
with  the  seepage  water,  though  there  is  some  reduction  in  its  amount 
within  a  given  soil  depth  if  there  is  a  material  lowering  of  the  water 
table  of  the  soil.  However,  it  may  be  lost  through  evaporation  from  the 
surface  soil.  Hygroscopic  water  is  the  moisture  that  is  to  be  found  in 
air-dry  soil  exposed  to  a  moist  or  saturated  atmosphere.  Like  capillary- 
water  it  exists  in  the  form  of  thin  films  adhering  to  the  surface  of  the  soiL 
The  films,  however,  are  much  thinner  than  those  of  capillary  moisture 
and  the  soil  retains  this  hygroscopic  water  with  great  tenacity.  The 
capillary  and  hygroscopic  moisture  together  may  be  regarded  as  a  product 
of  what  the  soil  particle  can  hold  against  the  pull  of  gravity  on  the 
one  hand  and  the  evaporating  power  of  the  air  on  the  other. 

47 


48 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


The  maximum  amount  of  water  that  a  given  soil  may  contain  depends  on 
the  volume  of  its  pore  space.  Both  may  range  from  about  32  to  a  Uttle  over  52 
per  cent.'^'  This  amount  of  water  is  equivalent  to  a  4  to  6  acre-inch  precipitation 
and  would  weigh  from  20  to  32  pounds  per  cubic  foot  of  soil.  Naturally  these 
large  amounts  of  water  are  not  found  in  any  soil  except  below  the  water  table  line 
or  immediately  after  heavy  precipitation  or  irrigation  and  before  drainage  has  had 
an  opportunity  to  carry  away  the  surplus  moisture.  It  is  the  amounts  of  capil- 
lary and  hygroscopic  water  that  a  soil  will  retain  rather  than  its  total  water-holding 
capacity  as  determined  by  pore  space  that  are  of  interest  in  fruit  growing,  for  the 
reason  that  little  or  none  of  the  free  or  gravitational  water  is  utihzed  by  the 
plants.  For  most  purposes  and  under  most  conditions  it  is  only  the  capillary 
moisture  that  they  use,  though  Loughridge**^  is  responsible  for  the  statement 
that  in  some  instances  plants  are  able  to  remain  alive,  even  though  they  cannot 
grow,  in  soils  whose  water  supply  is  reduced  to  the  point  where  only  hygroscopic 
moisture  is  present.  The  total  amount  of  capillary  water  that  a  soil  will  retain 
depends  not  so  much  on  the  pore  space  as  on  the  size  of  the  soil  particles 
and  the  distance  from  the  level  of  the  ground  water  below.  Tables  27  and  28 
show  the  percentage  of  water  that  certain  typical  soils  will  hold  as  capillary 
moisture  against  the  force  of  gravity.  These  figures  were  obtained  from  soils 
of  undisturbed  field  texture  several  days  after  heavy  rains  so  that  gravitational 
water  had  had  ample  opportunity  to  drain  away.  It  should  be  stated  in  con- 
nection with  these  tables,  that  in  each  case  the  soil  became  somewhat  more  sandy 
at  greater  depths. 


Table   27. — Amounts   of   Capillary    Moisture   Held   Against 
Gravity  in  Certain  Typical  Soils" 

THE   Force   of 

Depth 

Sandy  loam, 
per  cent. 

Clay  loam, 
per  cent. 

Humus  soil, 
per  cent. 

First  foot. 

17.65 
14.59 
10.67 

22.67 
19.78 
18.16 

44.72 

Second  foot       .... 

31.24 

Third  foot 

21.29 

Table  28.— Maximum  Capillars 

Capacity  of  Soils  for  Water 

Percentage 
of  water 

Pounds  of 
water  per 
cubic  foot 

Inches  of 
water 

32.2 
23.8 
24.5 
22.6 
17.5 

23.9 
22.2 
22.7 
22.1 
19.6 

4.59 

Second  foot  of  reddish  clay 

4.26 

Third  foot  of  reddish  clay 

4.37 

Fourth  foot  of  clay  and  sand                   .  .  . 

4.25 

Fifth  foot  of  fine  sand 

3.77 

It  is  interesting  to  note  that  the  optimum  condition  for  the  growth 
of  plants  is  afforded  by  a  soil  when  the  capillary  water  amounts  to  between 
40  and  60  per  cent,  of  the  total  water-holding  capacity  of  the  soil,  leaving 


SOIL  MOISTURE  49 

from  60  to  40  per  cent,  air  space.  Desert  plants  or  plants  coming  from 
dry  climates  are  more  tolerant  of  deficiency  in  soil  moisture  and  the  opti- 
mum capillary  moisture  content  for  these  plants  is  lower.  The  reverse 
is  true  of  certain  other  plants  that  thrive  under  moist  conditions.  The 
almond  is  mentioned  by  Hilgard  and  Loughridge^^  as  suffering  from  excess 
moisture  when  approximately  three-fourths  of  the  pore  space  was  filled 
with  water. 

The  hygroscopic  moisture  of  the  soil  varies  greatly  with  the  composition. 
In  sandy  soils  it  may  be  as  low  as  2  or  3  per  cent,  and  in  coarse  sands  even  lower. 
In  ordinary  loams  it  ranges  from  4  to  5  per  cent,  and  in  heavy  clays  and  adobes 
it  may  be  as  high  as  8  or  10  per  cent.^" 

The  Relative  Saturation. — Brown^^  suggested  that  a  more  useful  way 
of  expressing  the  water  content  of  the  soil  would  be  in  terms  of  its  relative 
saturation.  This  would  take  into  account  the  maximum  water  capacity 
as  well  as  the  actual  water  content  and  would  afford  a  more  accurate 
index  of  the  biological  or  physiological  wetness  of  the  soil  than  the 
standards  of  measurement  now  employed.  In  commenting  upon  this 
question  of  relative  saturation  he  says : 

"The  water  content  alone  is  .  .  .  but  an  imperfect  index  of  the  soil  con- 
ditions. Since  soils  of  different  mechanical  composition  have  different  capacities 
for  water,  the  same  quantity  of  water  produces  different  changes  in  humidity  in 
these  different  soils.  For  example,  the  quantity  of  moisture  sufficient  to  saturate 
a  given  mass  of  sandy  soil  is  insufficient  to  saturate  a  like  mass  of  humous  soil. 
The  degree  of  wetness  or  dryness,  of  a  soil,  therefore,  really  depends  on  the 
amount  of  water  which  the  soil  can  still  take  in  before  being  saturated.  Con- 
sequently, a  more  perfect  index  to  the  'wetness '  or  'dryness '  of  a  soil  is  to  be  had 
by  expressing  the  water  content  of  the  soil  in  terms  of  its  maximum  water  capacity, 
,,         , .      Water  content 

the  ratio  ^^^^^^^^^  capacity'  ^^^"^  ^^"^^^  ^^^  ^^^^^^^  Saturation  of 
the  soil  .  .  .  This  value,  and  not  the  actual  water  content  itself,  will  be  the  index 
to  the  '  biological  wetness'  of  the  soil  ...  in  comparing  two  soils  whose  actual 
moisture  contents  are  different,  say,  the  ratios  may  indicate  that  both  soils, 
however,  have  the  same  degree  of  wetness,  and  so,  in  relation  to  the  physiological 
action  of  the  plant  are  of  similar  conditions." 

Resistance  to  Freezing. — Another  classification  of  the  soil  water  is 
made  by  Bouyoucos.^^  This  classification  is  based  upon  freezing  point 
determinations  with  the  dilatometer.  Water  which  freezes  at  or  slightly 
below  0°C.  is  termed  free  water,  that  which  freezes  between  0°C.  or  a 
little  below  and  —  78°C.  is  termed  capillary  or  capillary-adsorbed  water 
and  that  which  does  not  freeze  except  at  temperatures  below  —  78°C,  is 
termed  combined  water.  These  classes  do  not  coincide  exactly  with  those 
of  the  classification  used  before  and  they  serve  to  bring  out  some  of  the 
features  of  the  water  supply  of  the  soil  that  have  been  overlooked  and 


50  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

that  investigations  indicate  are  intimately  associated  with  the  question 
of  winter  injury. 

Bouyoucos"  points  out  that  the  relative  amounts  of  these  forms  of  water 
vary  greatly  in  different  soils.  He  says:  "In  some  soils  only  one  or  two  forms 
predominate,  while  in  others  all  three  are  about  equally  represented.  In  the 
sands  and  fine  sandy  loams,  it  is  the  free  water  that  predominates,  which  amounts, 
in  some  cases,  to  about  95  per  cent,  of  the  total  water  present;  the  other  5  per 
cent,  consists  as  a  rule,  of  combined  water;  capillary  adsorbed  water  is  apparently 
not  present  in  these  classes  of  soil.  In  the  loams  and  silt  loams,  it  is  the  free 
and  combined  water  which  predominates.  Here,  again  the  capillary-adsorbed 
water  is  present  in  small  amounts.  In  some  of  the  heavy  loams  all  three  forms 
are  about  equally  distributed.  In  clay  loams  and  humus  loams  and  clay,  it  is 
the  combined  water  which  predominates  followed  by  capillary-adsorbed  and 
free.  Although  the  amount  of  free  water  tends  to  decrease  and  the  amount  of 
the  capillary-adsorbed  and  combined  water  tends  to  increase  correspondingly  as 
the  soils  ascend  from  the  simple  and  non-colloidal  to  the  complex  and  colloidal 
classes.     There  are  many  exceptions  to  this  rule."" 

Of  equal  importance  are  the  differences  in  the  amounts  of  free  or 
easily  frozen  water  in  plant  cells,  as  determined  by  McCool  and  Millar, ^^ 
using  the  dilatometer.  The  differences  found  suggest  corresponding 
differences  in  the  amounts  of  adsorbed  water  in  plant  cells. 

The  different  water-absorbing  capacity  of  plant  cells  is  attributed  by  Spoehr^^s 
to  their  pentosan  content.  This  is  confirmed  by  the  work  of  Hooker.'^^  It  seems 
probable,  therefore,  that  the  chemical  composition  of  plant  tissue,  as  of  soils, 
has  a  most  important  bearing  on  the  condition  in  which  its  water  is  held.  This 
in  turn  has  a  direct  relation  to  the  susceptibility  of  plant  tissue  to  environmental 
changes,  a  subject  that  is  discussed  in  greater  detail  in  the  section  on  Tempera- 
ture Relations. 

McCool  and  Millar  ^^  measured  the  amounts  of  easily  frozen  water  in  plants 
grown  in  soils  of  high,  medium  and  low  water  content.  They  found  that  the 
plants  grown  in  soils  of  high  water  content  contained  more  easily  frozen  water. 
Rosa"''  has  shown  that  with  lower  moisture  content  of  the  soil  there  is  an  increase 
in  the  pentosan  content  of  the  plants  grown  in  it.  This  amphfies  the  discovery 
that  pentosans  are  produced  under  xerophytic  conditions  and  that  the  water- 
retaining  capacity  of  the  cells  is  thereby  increased.  ^'^^  The  greater  amount  of 
adsorbed  water  that  such  plants  contain  would  mean  the  presence  of  smaller 
amounts  of  free  or  easily  frozen  water,  such  as  McCool  and  Millar  found.  These 
investigators  have  also  shown  a  correlation  between  the  depression  of  the  freezing 
point  of  plant  sap  and  the  amount  of  easily  frozen  water  it  contains;  the  lower 
the  freezing  point  the  less  easily  frozen  water  is  present. ^^  This  suggests  that 
differences  in  the  concentration  of  cell  sap  may  be  due  in  part  to  the  relative 
amounts  of  free  and  adsorbed  water.  It  is  obvious  that  with  a  given  amount  of 
soluble  material,  the  concentration  of  the  sap  will  depend  on  the  amount  of  free 
water  available  for  its  solution.  The  less  the  proportion  of  free  water  and  the 
greater  the  proportion  of  adsorbed  water  the  higher  the  concentration  of  the 
solution. 


SOIL  MOISTURE  51 

These  differences  in  condition  of  the  water  present  are  important  in 
practical  ways.  They  explain  the  increased  moisture  requirement  of  a 
plant  grown  in  moist  surroundings;  their  application  in  cold  resistance  is 
shown  elsewhere ;  it  is  possible  that  the  greater  adaptability  of  some  plants 
to  varied  environments  is  related  to  their  capacity  of  forming  water 
retaining  substances.  These  water  retaining  substances  represent  a 
mechanism  for  the  retention  of  moisture  by  living  plant  cells,  a  mechanism 
which  is  entirely  distinct  from  that  represented  by  the  anatomical  modifi- 
cations characteristic  of  xerophytic  or  semi-xerophytic  plants.  The 
former  has  to  do  with  the  loss  of  water  from  the  cells  to  the  intercellular 
spaces;  the  latter  with  the  loss  of  water  from  the  plant  tissue  to  the 
outside.  The  two  means  of  protection  against  water  loss  may  occur 
together  in  which  case  the  effectiveness  of  each  would  be  increased,  but 
they  may  be  quite  independent  of  each  other. 

MOVEMENT  OF  WATER  IN  THE  SOIL 

After  water  once  reaches  the  soil,  following  either  natural  precipitation 
or  irrigation,  it  becomes  subject  to  the  forces  of  gravity  and  surface 
tension  and  in  a  general  way  these  may  be  said  to  control  its  movement. 
Percolation  downward  represents  the  result  of  the  two  forces  working 
together.  Lateral  movement  and  rise  by  capillarity  represent  what  the 
force  of  surface  tension  is  able  to  do  in  opposition  to  the  force  of  gravity. 

Percolation. — It  has  been  pointed  out  that  optimum  growing  condi- 
tions for  most  crop  plants  are  found  when  from  40  to  60  per  cent,  of  the 
total  pore  space  of  the  soil  is  filled  with  capillary  water.  Immediately 
after  heavy  rains  the  soil  moisture  occupies  a  larger  percentage  of  pore 
space  in  the  soil.  Therefore,  the  movement  of  water  through  the  soil 
must  be  considered.  In  humid  regions  its  vertical  movement  is  of  chief 
interest;  in  irrigated  sections  both  its  vertical  and  its  lateral  movement 
are  important.  Few  realize  the  rate  at  which  water  percolates  through 
the  soil  and  the  percentage  of  the  total  precipitation  or  of  the  total 
amount  applied  by  irrigation  that  is  lost  in  this  way.  Table  29  averages 
the  percolation  data  obtained  during  a  period  of  34  years  at  the  Rotham- 
sted  Experiment  Station  on  a  rather  heavy  loam,  or  clay  loam  soil.  It 
shows  the  amounts  of  water  percolating  through  the  soil  columns  20, 
40  and  60  inches  deep. 

Attention  is  directed  particularly  to  the  great  difference  between  the 
proportions  of  rainfall  removed  by  seepage  in  years  of  light  and  years  of 
heavy  fainfall.  The  figures  also  show  a  much  higher  percentage  of 
percolation  during  winter  months  when  there  is  comparatively  little 
evaporation  than  during  the  summer  months  when  the  evaporation 
rate  is  high.  As  a  rule,  the  hghter  the  soil,  the  larger  is  the  percentage  of 
percolation  water.     Consequently  in  the  irrigation  of  hght  soils  it  is 


52  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Table  29. — Rate  of  Percolation  of  Water  Through  Clay  Loam  Soil'" 


Inches 

of 
rain- 
fall 


Inches  of  water  drained 
through  soil  columns 


Per  cent,  of  rainfall  per- 
colating through  soil 
column 


20  40 

inches     inches 
deep        deep 


inches 
deep 


20 

40 

nches 

inches 

deep 

deep 

60 
Inches 
deep 


January .  .  . 
Februarj' . . 

March 

April 

May 

June 

July 

August . . . . 
September 
October.  . . 
November 
December. 


2.32 
1.97 
1.85 
1.89 
2.11 
2.36 
2.73 
2.67 
2.52 
3.20 
2.86 
2.52 


1.82 
1.42 
0.87 
0.50 
0.49 
0.63 
0.69 
0.62 
0.88 
1.85 
2.11 
2.02 


2.05 
1.57 
1.02 
0.57 
0.55 
0.65 
0.70 
0.62 
0.83 
1.84 
2.18 
2.15 


1.96 
1.48 
0.95 
0.53 
0.50 
0.62 
0.65 
0.58 
0.76 
1.68 
2.04 
2.04 


78.5 
72.2 
47.6 
26.5 
23.2 
24.0 
25.3 
23.2 
35.0 
57.8 
76.7 
80.3 


88.4 
80.0 
55.6 
30.0 
26.1 
27.6 
25.6 
23.2 
32.8 
57.5 
76.3 
85.4 


84.5 
75.2 
52.0 
28.0 
23.6 
26.3 
23.8 
21.7 
30.0 
52.3 
72.4 
81.0 


Mean  total  per  year. 


28.98 


13.90 


14.73 


13.79 


48.2 


51.0 


48.0 


Results  for: 
Maximum  rainfall. 
Minimum  rainfall. 


38.70 
20.50 


23.50 

7.32 


23.60 
7.90 


24.30 

7.70 


60.7 
35.7 


61.0 

38.5 


63.0 
37.6 


generally  necessary  to  use  more  water  than  in  heavy  soils  under  similar 
climatic  conditions  and  with  the  same  fruits.  The  extra  amount  of 
water  required  by  such  soils  may  be  reduced  somewhat  by  lighter  and 
more  frequent  applications,  but  this  too  may  be  carried  to  an  extreme  and 
result  in  an  unnecessary  waste  through  evaporation.  An  illustration  of 
this  principle  is  furnished  by  certain  orchards  on  the  Umatilla  Irrigation 
Project  in  eastern  Oregon.  Many  orchards  on  this  project  have  required 
7  or  8  acre-feet  of  water  in  order  to  bring  a  crop  of  fruit  to  maturity, 
though  the  trees  themselves  could  use  only  9  or  10  inches.  Evaporation 
rates  in  the  climate  of  that  section  are  very  high,  but  the  main  reason 
for  applying  9  to  10  times  more  than  the  trees  actually  use  is  the  extremely 
high  percolation  through  light  porous  sandy  soils  and  subsoils. 

The  Rise  Of  Water  By  Capillarity.  —It  is  often  thought  that  much  of 
the  water  that  percolates  through  the  soil  again  rises  by  capillary  action 
and  becomes  available  to  the  trees  later  in  the  season.  Investigations 
of  recent  years  tend  to  minimize  the  importance  of  this  upward  movement 
of  soil  moisture.  The  generally  accepted  opinion  of  the  present  may  be 
summarized  in  the  following  statement  by  Rotmistrov;!"^     "As  regards 


SOIL  MOISTURE 


53 


the  mechanical  raising  of  water,  however,  by  capillary  action  it  may  be 
assumed  that  the  limit  from  which  water  can  make  its  way  upward  lies 
much  higher  than  the  limit  accessible  to  the  roots.  All  the  data  at  my 
command  regarding  moisture  in  the  soil  of  the  Odessa  Experimental 
field  point  only  to  one  con- 
clusion, namely,  that  water 
percolating  beyond  the  depth 
of  40  to  50  centimeters  (16  to 
20  inches)  does  not  return  to 
the  surface  except  by  way  of 
the  roots."  Briggs,  Jensen 
and  McLane,23  in  reporting 
upon  the  results  of  irrigation 
experiments  in  citrus  groves 
in  California  state  that  avail- 
able soil  moisture  below  the 
third  foot  did  not  prevent 
orange  trees  from  wilting 
when  the  moisture  content 
in  the  first  3  feet  of  soil  fell 
below  its  wilting  coefficient 
and  the  roots  of  the  trees  were 
limited  to  the  first  3  feet. 
This  is  a  point  that  must  be 
kept  in  mind  in  irrigation 
practice  for  it  means  that 
trees  can  utilize  the  moisture 
supply  in  the  volume  of  the 
soil  that  the  roots  occupy, 
but  very  little  that  percolates 
to  or  stands  at  a  lower  level. 
In  other  words,  the  tree  can 
make  use  of  the  water  supply 
at  3  or  4  or  5  or  10  feet  in 
depth  only  to  the  extent  that 
it  can  develop  a  root  system 
that  penetrates  to  these 
depths. 

Lateral  Movement  of  Water  in  the  Soil. — The  lateral  movement  of 
water  in  soils  is  likewise  dependent  largely  upon  texture,  though  the 
amount  and  kinds  of  soluble  mineral  salts,  the  soil  colloids,  the  organic 
material  and  other  factors  have  their  influences.  In  open,  porous  soils, 
water  spreads  laterally  to  a  considerable  distance  and  with  comparative 
rapidity.     In  heavy,  compact  soils,  its  lateral  spread  is  slight  and  slow. 


20 


40 


50 


GO 


30 
Days 

Fig.  3. — Rate  of  movement  of  moisture  in  soil 
in  horizontal  open  flumes.  Figures  in  circles  indi- 
cate points  at  which  that  number  of  liters  of  water 
had  been  taken  up.  The  dotted  line  for  flume  No. 
71  (covered)  is  for  comparison  with  flume  No.  70 
(open).     {After  McLaughlin.^^) 


54  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

For  instance,  in  one  experiment  on  a  heavy  soil  in  California,  after  an 
irrigation  considered  sufficient  to  last  about  four  weeks,  the  moisture 
was  found  to  have  penetrated  laterally  only  about  eighteen  inches  from 
the  irrigation  furrow. ^^  Figure  3  shows  graphically  the  rate  of  this 
lateral  spread  as  it  takes  place  through  the  force  of  capillarity  and  unaided 
by  gravity.  The  spacing  of  irrigation  furrows  must  be  made  accordingly, 
if  the  entire  volume  of  the  soil  is  to  be  wetted.  It  is  for  this  reason  that 
basin  irrigation  or  flooding  is  sometimes  preferred  to  furrow  irrigation  in 
comparatively  heavy  land. 


THE  DISTRIBUTION   OF  FRUIT  TREE  ROOTS  AS  INFLUENCED  BY  SOIL 

MOISTURE 

The  size  and  distribution  of  the  root  system  depends  upon  the  opera- 
tion of  many  factors,  such  as  the  moisture  supply,  aeration  of  the  soil 
and  nutrient  supply.  In  most  cases  it  is  impossible  to  assign  to  each 
factor  the  part  it  has  played,  but  as  they  are  more  or  less  interdependent 
they  may  be  discussed  together. 

The  Ideal  Root  System. — Deep  rooting  is  desirable  for  the  purpose 
of  making  the  water  (and  nutrient)  supply  contained  in  a  large  volume 
of  soil  available  to  the  plant.  For  the  same  reason  there  should  be  at 
least  a  moderate  lateral  spread.  In  other  words  the  tree,  or  other 
fruit-producing  plant,  that  is  equipped  with  an  extensive  root  system 
will  be  able  better  to  endure  extremes  of  drought  or  temperature  or 
exceptional  demands  for  a  supply  of  nutrients,  than  one  with  a  limited 
root  system.  Plants  grown  in  a  comparatively  concentrated  nutrient 
solution  or  in  rich  soil  have  roots  that  are  shorter,  more  branched  and 
more  compact  than  those  grown  in  a  weak  nutrient  solution  or  in  a 
poor  soil.  Changing  fertility  is  one  explanation  of  the  marked  contrasts 
in  the  degree  of  ramification  of  roots  as  they  penetrate  different  strata.  ^^ 
The  ideal  root  system  is,  therefore,  not  the  one  with  branches  that  reach 
out  or  down  the  farthest,  but  the  one  that  more  or  less  fully  explores 
and  occupies  the  soil  to  a  reasonable  depth  and  within  a  reasonable 
radius.  Otherwise,  it  would  be  necessary  to  regard  the  root  system  pro- 
duced only  in  an  infertile  soil  as  the  ideal. 

Specific  and  Varietal  Differences  in  Root  Distribution. — Depth  of 
rooting  and  lateral  spread  of  roots  depend  in  the  first  place  on  the  species 
or  variety  of  plant.,  Some,  like  the  walnut  and  pecan,  are  character- 
istically deep  rooted;  others  like  the  spruces  and  hemlocks  and  the  river 
bank  grape  {Vitis  riparia)  are  characteristically  shallow  rooted.  The 
roots  of  certain  fruit  varieties,  like  the  Wealthy  apple,  are  strong,  stocky 
and  far  ranging;  those  of  other  varieties,  like  certain  strains  of  the  Doucin, 
are  short,  slender,  compact  and  much  branched.  These  characteristics 
should  be  borne  in  mind  when  selecting  fruits  or  fruit  stocks  for  particular 


SOIL  MOISTURE  55 

soils  and  when  considering  the  influence  of  various  environmental  factors 
and  cultural  practices  upon  root  distribution,  for  though  root  distri- 
bution is  influenced  profoundly  there  are  limits  to  the  plasticity  of  any 
species;  nothing  stated  in  this  connection  should  be  construed  as  im- 
plying that  these  usual  limits  for  the  species  or  variety  may  be  exceeded. 

The  Distribution  of  Tree  Roots  under  Varying  Conditions. — Tree 
roots  often  range  deep,  but  such  investigations  as  have  been  reported 
show  a  surprisingly  shallow  root  system  in  most  of  our  orchard  planta- 
tions, at  least  in  the  humid  regions. 

In  the  Hood  River  Valley,  Oregon  and  in  Ohio. — For  instance  a  report 
upon  the  condition  of  the  root  system  of  apple  trees  in  the  Hood  River 
valley  states: 

"It  was  found  that  the  majority  of  the  feeding  roots  of  fruit  trees  of  bearing 
age  were  located  from  3  to  10  inches  below  the  surface  of  the  soil."^  A  discussion 
of  the  root  systems  of  apple  trees  in  Ohio  includes  the  following  statement:  "The 
main  root  systems,  of  apple  trees,  under  the  different  methods  of  culture  (clean 
culture  with  cover  crops,  sod  culture,  and  sod  mulch),  were  found  to  be  at  a  sur- 
prisingly uniform  depth — the  greater  portion  of  the  roots,  both  large  and  minute, 
being  removed  with  the  upper  6  inches  of  soil.  .  .  .  The  fibrous  or  feeding-root 
sj'^stem  of  a  tree  under  annual  plowing  and  clean  culture  with  cover  crops,  practi- 
cally renews  itself  annually — pushing  up  thousands  of  succulent,  fibrous  rootlets 
to  the  very  surface  of  the  soil  where  they  actually  meet  with  the  steel  hoes  or 
spikes  of  the  cultivator  or  harrow,  especially  in  seasons  when  moisture  is  abun- 
dant. Apparently  but  a  small  percentage  of  these  rootlets  penetrate  the  lower, 
more  compact  colder  soil,  but  they  come  to  feed  where  warmth  and  air  and  mois- 
ture combine  to  provide  the  necessary  conditions  for  root  pasturage.  As  a  matter 
of  fact,  these  feeding  rootlets  are  cleanly  pruned  away  by  the  plowshare  each 
succeeding  year,  and  without  apparent  injury  to  the  trees  or  crops."" 

The  writers  then  go  on  to  state  that  the  destruction  of  the  roots  in 
the  upper  2  or  3  inches  of  soil  by  summer  drought  or  by  winter  cold  re- 
sults in  no  serious  injury  to  the  tree,  as  those  ranging  deeper,  4  to  6 
inches,  can  take  care  of  the  tree's  requirements. 

In  a  Gravelly  Loam,  Underlaid  by  Hardpan,  in  Maine. — Some  valuable 
data  on  the  root  distribution  of  apple  trees  growing  under  different  soil 
conditions  were  obtained  by  Jones"  in  Maine.  Figures  4  and  5  show  photo- 
graphs of  the  tree  roots  obtained  from  a  square  foot  of  soil  midway  be- 
tween two  Baldwin  trees  set  27  feet  apart  and  about  28  years  old.  The 
photographs  show  the  roots  in  successive  layers  of  soil  4  inches  thick. 
This  soil  was  a  gravelly  loam  to  a  depth  of  2  or  23^^  feet  where  a  rather 
impervious  hardpan  was  encountered.  Figure  4  shows  roots  growing  in 
a  rather  wet  portion  of  the  orchard;  those  in  Fig.  5  were  from  a  drier 
portion.  The  tops  of  these  trees  were  not  meeting,  yet  in  both  the  wet 
and  dry  areas  their  roots  were  interlacing  and  the  soil  to  a  depth  of  over 
2  feet  was  more  or  less  thoroughly  exploited.     Though  the  greatest  ex- 


56 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


SOIL  MOISTURE 


57 


■  -  a 


58 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


pansion  of  the  root  system  was  in  the  4-  to  8-inch  layer,  there  was  a 
fairly  large  number  of  roots  20  inches  deeper.  There  was  also  much 
better  expansion  of  the  root  system  at  both  upper  and  lower  levels  in 
the  drier  soil  than  in  the  one  classed  by  Jones  as  a  little  too  wet  for  the 
best  growth  of  the  apple  tree.  The  question  is  raised  by  Jones  as  to 
whether  interlacing  of  roots  is  not  evidence  that  for  a  number  of  years 
these  trees  had  been  suffering  from  lack  of  room,  a  suggestion  supported 
by  the  indifferent  performance  of  the  orchard  for  some  time  previous. 

Table  30  shows  the  length  of  the  roots,  in  feet,  found  in  each  cubic 
foot  of  soil  at  successive  distances  from  the  tree  trunk.  These  measure- 
ments were  taken  for  a  Milding  apple  tree  9.33  inches  in  diameter  2  feet 
from  the  ground,  with  an  11-foot  spread  of  branches,  and  growing  in  a 
stony  loam.  The  last  column  shows  the  computed  length  of  roots  for  the 
cylinder  of  soil  1  foot  in  thickness  surrounding  the  tree  at  a  given  distance 
from  the  trunk,  assuming  that  the  section  examined  is  typical  for  the 
entire  area  of  which  the  tree  is  the  center.  Figure  6  shows  graphically 
the  data  presented  in  Table  30.  They  afford  some  idea  of  the  relatively 
extensive  development  of  a  tree's  root  system  under  conditions  that  are 


Table  30. — Root  Distribution  of  a  25-year  Old  Apple  Tree,   Measured  by 

Sections 
(After  Jones''^) 


Distance  of 
section  in  feet 
from  tree  trunk 

Length  of  roots 

Length  of  roots 

Total  length 

Computed 

in  first  6- 

in  second  6- 

of  root  in 

length  for 

inch  layer  of 

inch  layer  of 

cubic  foot  of 

cylinder  about 

soil,  feet 

soil,  feet 

soil,  feet 

trunk,  feet 

1 

112 

32 

144 

144 

2 

66 

109 

175 

1650 

3 

19 

74 

93 

1460 

4 

3 

72 

75 

1650 

5 

0 

28 

28 

792 

6 

3 

48 

51 

1712 

7 

0 

48 

48 

2008 

8 

0 

32 

32 

1508 

9 

4 

72 

76 

4059 

10 

0 

35 

35 

2089 

11 

5 

37 

42 

2771 

12 

4 

16 

20 

1445 

13 

3 

26 

29 

2278 

14 

0 

18 

18 

1527 

15 

0 

12 

12 

1093 

16 

0 

8 

8 

779 

17 

6 

2 

8 

829 

18 

0 

8 

8 

880 

19 

0 

7 

7 

814 

20 

0 

^2 

M 

61 

SOIL  MOISTURE 


59 


presumably  more  or  less  common.  In  this  case  plowing  and  cultivating 
to  a  depth  of  6  inches  would  have  destroyed  a  little  less  than  one-tenth 
of  the  conducting  roots.  The  percentage  of  the  very  small  absorbing 
and  feeding  roots  would  not  necessarily  be  the  same.  Over  19,000  of 
the  total  of  29,547  feet  of  conducting  roots,  in  other  words  about  65  per 
cent.,  lie  beyond  the  spread  of  its  branches.  Probably  the  proportion 
of  feeding  roots  is  still  greater.  Irrigation  water  and  fertilizers  should  be 
distributed  accordingly;  the  treatment  of  the  small  area  of  soil  immediately 
surrounding  a  large  bearing  tree  which  is  difficult  of  access  with  the  tools 
of  cultivation  would  seem  to  be  of  small  importance  so  far  as  either  water 
or  nutrient  supply  is  concerned. 

120 


iJ  GO 
+i  50 


I     2     3     4     5     e     1     8     9     10    II     l^    \3    14    15    16    n 
Dis+ance  from  Tree,feet 

Fig.  6. — Distribution  of  apple  roots  in  surface  six  inches  and  second  six  inches  in  a 
soil  section  one  foot  wide  in  rather  heavy  loam.  Solid  line  shows  surface  layer;  broken 
line  shows  second  layer.      {After  JonesJ^) 


\l 

\ 

\ 
\ 

._, 

1 

/ 

\ 

1 

\ 

/ 

\ 

1 

\ 

/ 

\ 

/ 

\ 

/ 

\ 

\ 

— ■ 

\ 

y 

\ 

\, 

'' 

'■>»^ 

s 

^ 

^^ 

^ 

^ 

^ 

— 

^ 

^ 

< 

"~- 

*^, 

In  a  Thin  Gravelly  Loam,  Underlaid  hy  Rock,  in  Maine. — The  data 
given  in  Table  31  represent  extreme  conditions.  They  are  for  an  under- 
sized, stunted  seedling  apple  tree  probably  40  years  old,  on  level  ground 
at  the  top  of  a  hill  thinly  covered  with  a  rocky,  gravelly  clay  loam  The 
soil  was  less  than  a  foot  deep  and  was  underlaid  by  rock  or  ledge  or  with  a 
heavy  clay  mixed  with  gravel.  For  many  years  the  orchard  had  been  in 
pasture  and  the  trees,  having  received  practically  no  care,  had  experienced 
a  hard  struggle  for  existence  and  many  had  died. 

Without  doubt,  limited  nutrient  as  well  as  limited  moisture  supply  had 
been  an  important  factor  in  forcing  this  tree  to  extend  its  root  system  so 
far  and  wide  in  order  to  hold  on  in  its  struggle  for  existence.  Whatever 
may  have  been  the  exact  combination  of  factors  leading  to  this  develop- 
ment it  shows  a  marked  power  of  adaptation  on  the  part  of  the  plant.  It 
also  carries  the  suggestion  that  in  soils  where  deep  rooting  is  impossible 
the  spacing  of  trees  and  other  fruit  plants  should  be  much  wider  than 
under  more  favorable  conditions. 


60 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Table  31. — Root  Distribution  of  a  40-yeak  Old  Apple  Tree  in  a  Thin  Rocky 

Soil  Under  Sod  for  Many  Years 

(After  Jones''^) 


Distance 

Length 

Length 

Distance 

Length 

Length 

of  section 

of  roots 

of  roots 

Total 

of  section 

of  roots 

of  roots 

Total 

from 

in  top 

in  next 

length, 

from 

in  top 

in  next 

length. 

trunk, 

6  inches, 

6  inches. 

feet 

trunk, 

6  inches, 

6  inches, 

feet 

feet 

feet 

feet 

feet 

feet 

feet 

1 

64 

96 

160 

16 

32 

2 

34 

2 

98 

22 

120 

17 

10 

0 

10 

3 

20 

50 

70 

18 

6 

7 

13 

4 

34 

80 

104 

19 

6 

14 

20 

5 

54 

34 

88 

20 

8 

12 

20 

6 

22 

4 

26 

21 

8 

0 

8 

7 

14 

7 

21 

22 

11 

3 

14 

8 

17 

18 

35 

23 

3 

8 

11 

9 

16 

26 

42 

24 

3 

5 

8 

10 

0 

0 

0 

25 

0 

7 

7 

11 

0 

10 

10 

26 

2 

0 

2 

12 

6 

9 

15 

27 

5 

7 

12 

13 

12 

12 

24 

28 

0 

2 

2 

14 

28 

23 

51 

29 

0 

2 

2 

15 

0 

18 

18 

In  Dwarfs.- — In  contrast  with  the  comparatively  extensive  root 
systems  of  trees  growing  in  the  field  are  those  of  dwarfs  occasionally 
grown  in  the  garden  or  under  glass  whose  growth  is  restricted  by  various 
means.  Sometimes  resort  is  made  to  root  pruning;  sometimes  the  roots 
are  restricted  by  planting  in  pots  or  tubs.  Such  trees  develop  very  com- 
pact and  much  branched  root  systems  that  exploit  very  completely  the 
soil  within  their  range.  Dwarf  trees  with  such  restricted  root  systems 
are  much  more  subject  to  injury  from  extremes  of  moisture  than  standards 
with  unrestricted  root  systems.  Consequently  their  successful  culture 
necessitates  much  greater  care  in  watering,  fertilization,  pruning,  exposure 
to  light  and  management  in  general. 

The  Influence  of  Soil  Moisture  Content.- — Within  the  ranges  possible 
for  the  different  species,  depth  of  rooting  depends  to  a  very  important 
extent  on  soil  moisture  and  the  correlated  factor,  aeration.  Roots  do 
not  grow  and  branch  freely  in  a  very  dry  soil,  or  in  one  that  is  approach- 
ing a  water-logged  condition.  The  water-logged  soil  probably  inhibits 
root  growth  and  activity  through  a  lack  of  aeration;  the  dry  soil  through 
a  lack  of  the  stimulating  effect  of  the  water  itself.  Figure  7  gives  some 
idea  of  the  influence  exerted  by  the  percentage  of  soil  moisture  on  root 
formation  and  root  distribution  when  other  factors  are  as  uniform  as  it  is 
possible  to  make  them.     In  this  case,  however,  the  soil  moisture  did  not 


SOIL  MOISTURE 


61 


approach  sufficiently  near  the  saturation  point  to  check  root  formation. 
When  roots  find  an  abundance  of  water  close  to  the  surface  they  branch 
freely  through  the  surface  soil  and  show  Httle  tendency  to  go  deeper, 
particularly  if  conditions  are  more  and  more  unfavorable  for  root  develop- 
ment at  greater  depths.  These  two 
factors  together  probably  explain  the 
comparatively  shallow  rooting  of 
most  tree,  bush  and  vine  fruits  in  a 
large  portion  of  the  humid  region. 
Compact,  water-logged  subsoils  or 
a  high  water  table  prevent  the  roots 
from  penetrating  deeply. "  The  sur- 
face inch  or  so  is  too  dry  during  a 
major  portion  of  the  growing  season 
to  encourage  root  growth ;  the  result  is 
a  distribution  of  most  of  the  roots  be- 
tween the  depths  of  3  to  10  or  15 
inches. 

When,  however,  moisture  and 
aeration  conditions  are  favorable  for 
root  development  at  considerable 
depths,  deep  penetration  occurs. 
Thus  Hilgard  and  Loughridge^^  state 
that  on  some  of  the  silty  "low  mesa" 
soils  of  California  the  roots  of  cherry 
and  prune  trees  are  frequently  found 
at  depths  of  20  to  25  feet.  Such  deep 
rooting  is  also  characteristic  of  fruit 
trees  in  the  loose  soils  along  the 
Mississippi  and  Missouri  rivers. 
"These  are  soils,  however,  with  no 
hardpan  or  plowsole  and  with  the  Sandy 
water  table  many  feet  below  the  sur-  '^''^S 
face.  In  them  soil  grades  insensibly 
into  subsoil.  Indeed,  subsoil  in  the 
sense  in  which  the  term  is  generally 
used,  does  not  exist  except  below  the 
region  of  this  exceptional  root  pene- 
tration. It  hardly  need  be  pointed  out  that  trees  in  such  soils  seldom 
suffer  from  drought,  even  though  there  may  be  a  series  of  dry  years. 

When  plants,  accustomed  to  growing  in  a  soil  where  shallow  rooting  is 
necessary,  are  transplanted  to  one  in  which  deep  penetration  is  possible, 
they  first  send  out  shallow  lateral  roots,  their  distribution  being  much 
like  that  of  the  same  plant  in  the  region  or  soil  from  which  it  came.     They 


Cloy 


bandy 
Clay 


Pure 
Sand 


Clay 


Sand 


Clay 


Fig.  7. — Influence  of  soil  moisture 
upon  root  distribution  of  Kuhnia  gluli- 
nosa.     {After  Weaver}^^) 


62  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

probably  encounter  in  the  surface  layers,  shortly  after  the  time  of  setting, 
those  conditions  of  air  and  moisture  approaching  the  optimum  for  growth. 
Then  as  the  season  progresses  and  the  surface  soil  dries,  the  roots  in 
many  cases  turn  down  and  send  branches  into  deeper  layers  and  a  distri- 
bution is  effected  resembling  that  of  native  plants.®^  This  may  be  looked 
upon  as  a  kind  of  adaptation,  an  accomodative  change,  to  meet  new  con- 
ditions of  environment.  That  this  change  in  rooting  habit  is  very  largely 
a  response  to  moisture  and  aeration  conditions  is  indicated  by  the  fact 
that  with  a  rise  in  the  ground  water  table  from  heavy  irrigation  the  roots 
are  again  forced  to  occupy  only  a  shallow  layer  of  soil.  This  condition  is 
found  in  some  of  the  orange  groves  of  California.  ^^  Three  or  four  feet 
beneath  the  surface  the  soil  is  so  water-logged  that  roots  will  not  penetrate 
and  the  top  6  or  8  inches  are  so  filled  with  feeding  rootlets  that  each 
cultivation  results  in  more  or  less  serious  root  pruning.  Trees  under  such 
conditions  require  heavier  irrigation  and  more  fertilization  than  those 
with  deeper  roots  and,  what  is  perhaps  more  important,  they  are  more 
sensitive  to  extremes  of  any  kind  affecting  the  roots  either  directly  or 
indirectly.  Consequently  they  are  more  exacting  in  their  cultural 
demands.  The  same  danger  from  heavy  irrigation  is  met  in  deciduous 
fruit  production.  Thus  it  has  been  found  in  Utah  that  raising  the  water 
table  even  temporarily  by  irrigation  causes  the  death  of  the  deeper  roots 
and  results  in  a  kind  of  root  pruning  or  root  training  and  that  the  general 
shape  of  the  root  system  of  the  tree  may  be  controlled  more  or  less  by  the 
distribution  of  the  iri'igation  water. ^  One  of  the  most  difficult  problems 
in  many  irrigated  sections  is  to  apply  the  water  in  such  a  way  that  plants 
are  not  made  surface  feeders  and  the  natural  advantages  of  a  deep  soil 
lost. 

The  Influence  of  Cultivation. — Allen^  found  that  tillage  methods  influenced 
root  distribution  in  the  Hood  River  district.  He  reports  that  where  clean 
culture  had  been  practiced  without  the  use  of  the  plow  but  with  disk  and  other 
cultivators  "a  thick  mat  of  fibrous  roots  was  found  immediately  below  the  soil' 
mulch.  ...  In  the  few  restricted  areas  that  received  neither  cultivation  nor 
irrigation,  the  roots  were  found  to  be  distributed  from  near  the  surface  to  1 
foot  and  16  inches  in  depth.  Under  sod  and  irrigation  conditions  the  roots  were 
quite  uniformly  distributed  from  near  the  surface  to  23-2  feet  in  depth."  Immedi- 
ately under  the  loose  surface  soil  of  the  cultivated  areas  he  found  an  impervious 
hardpan  or  plowsole  had  developed,  which  was  dry  at  the  time  of  this  examina- 
tion.    The  untilled  and  irrigated  land  did  not  have  this  hardpan  layer. 

Different  tillage  methods  had  resulted  in  great  variation  in  the  physical 
character  and  moisture  content  of  the  soil  between  the  depths  of  6  and 
30  inches,  and  in  corresponding  variations  in  root  distribution.  Evidently 
the  varying  tillage  methods  used  in  certain  Ohio  orchards^*  did  not 
change  materially  the  character  of  the  soil  below  a  depth  of  6  or  10 
inches  and  since  few  roots  developed  in  it  below  this  depth,  root  distri- 


SOIL  MOISTURE 


63 


bution  was  influenced  but  little  in  this  particular  case.  Cultivation  is 
mentioned  often  as  a  means  of  forcing  deeper  rooting  of  fruit  trees  and 
sod  culture  as  encouraging  shallower  rooting.  These  practices  often 
have  these  effects,  but  they  may  have  no  such  effect,  as  in  the  Ohio  investi- 
gation cited,  or  they  may  have  the  opposite  effects,  as  in  Hood  River. 
This  brings  out  the  point  that  tillage  methods  as  such  are  not  to  be 
regarded  as  direct  means  of  influencing  root  distribution,  but  as  means 
of  altering  the  physical  and  chemical  condition  of  the  soil  and  thus  indi- 
rectly leading  to  shallow  or  deep  penetration.  Root  growth  and  distri- 
bution is  a  response  to  these  physical  and  chemical  conditions.  It  is 
noteworthy  that  in  the  Hood  River  orchards  many  of  the  symptoms  of 
drought  injury  were  associated  with  extreme  shallow  rooting — premature 
dropping  of  the  foliage,  dieback  and  fruit-pit. 

Interesting  data  concerning  the  effect  of  cultivation  on  root  distri- 
bution are  afforded  by  the  figures  in  Table  32.  Cultivation  along  one 
or  both  sides  of  the  tree  row  reduced  the  absolute  lateral  spread  and  the 
ratio  between  the  lateral  spread  and  height  of  the  trees.  The  greater 
reduction  accompanied  cultivation  along  both  sides.  In  the  cultivated 
soil  the  tree  roots  did  not  have  to  range  so  wide  to  meet  the  actually 
increased  water  requirements  of  the  trees  as  in  the  uncultivated  land. 
Incidentally  the  figures  in  Table  32  throw  some  light  on  the  lateral 
spread  of  tree  roots  as  compared  with  the  spread  of  their  branches. 
Though  spread  of  top  is  not  given  it  is  reasonable  to  assume  that  in  this 
species  it  is  less  than  tree  height.  It  is  often  said  that  the  lateral  spread 
of  the  roots  is  about  equal  to  the  lateral  spread  of  the  branches.  In 
uncultivated  ground  it  was  in  this  instance  more  than  twice  as  great. 


Table  32. — Effect  of  Cultivation  Upon  Root  Spread  of 

THE  Osage  Orange^^ 

Amount  of 
cultivation 

Cases 
measured 

Average  lieight 
of  trees 

Average  root 
extent 

Average  root  extent; 
proportion  to  height 

8 
25 
35 

20.0 
17.2 
21.7 

43,7 
28.9 
29.2 

218.7 

One  side  of  trees .  . 
Both  sides 

167.8 
134.5 

Mason^^  cites  an  instance  in  which  the  olive  grown  in  an  extremely  dry  soil 
and  climate  had  a  root  system  radiating  10  to  11  feet  in  nearly  all  directions  when 
the  top  was  only  6  feet  in  height,  had  a  spread  of  only  7  feet  and  a  trunk  diameter 
of  3%  inches.  In  this  case  there  was  a  total  of  185  feet  of  roots  3-8  inch  or 
more  in  diameter  and  the  area  occupied  by  roots  of  this  size  was  about  nine 
times  that  of  the  spread  of  the  branches.  This  fruit  as  it  grows  in  the  Sfax 
region  of  Northern  Africa  furnishes  a  good  illustration  of  the  adaptation  of  the 
root  system  to  moisture  conditions.  There  it  sends  out  numerous  roots  which 
run  for  long  distances  comparatively  close  to  the  surface  where  they  can  make 
use  of  the  moisture  that  penetrates  only  a  few  inches  into  the  ground  at  the 
time  of  the  infrequent  light  rains. 


64  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

The  Influence  of  Soil  "Alkali.'' — It  should  not  be  inferred  from  the 
emphasis  that  has  been  placed  upon  moisture  and  aeration  in  determining 
root  distribution  that  other  factors  are  of  little  significance.  Other 
factors  are  often  controlling. 

For  instance  in  reporting  upon  an  investigation  of  the  effects  of  alkali  on 
citrus  trees  Kelley  and  Thomas^"  state:  "It  is  especially  interesting  that  the 
roots  of  the  lemon  trees  have  not  penetrated  deeply  in  this  soil,  more  than  95 
per  cent,  of  them  being  within  18  inches  of  the  surface.  There  is  probably 
some  connection  between  this  fact  and  the  higher  concentration  of  alkali  salts 
found  in  the  third  and  fourth  feet." 

Applications  to  Orchard  Practice. — The  whole  subject  of  the  distribu- 
tion of  the  root  system  of  orchard  plants  may  be  summarized  in  this  way : 
though  different  species  of  plants  and  different  varieties  of  the  same 
species  have  characteristic  habits  of  root  growth,  the  extent  and  the 
distribution  of  their  root  systems  are  profoundly  influenced  by  environ- 
ment. Root  development,  both  as  to  amount  and  direction,  may  be 
regarded  as  a  response  of  the  plant  to  this  environment.  The  functioning 
of  that  part  of  the  plant  above  ground  is  conditioned  to  a  very  important 
degree  by  the  functioning  of  the  part  of  the  plant  below  ground,  and 
therefore  by  the  distribution  of  the  roots  in  the  soil.  Root  distribution 
is  under  control  to  the  extent  that  soil  conditions — texture,  moisture, 
aeration  and  nutrient  supply — are  under  control  and  to  a  certain  extent 
by  the  pruning  that  is  afforded  the  top,  a  matter  discussed  in  detail  later. 
If  the  soil  is  one  in  which  these  conditions  are  not  favorable  for  a  suitable 
root  distribution  or  in  which  they  cannot  be  made  favorable,  it  should 
not  be  devoted  to  fruit  culture,  because  fruit  culture  cannot  be  successful 
on  it.  As  soon  as  the  orchard  is  planted,  or  before  if  possible,  and  as 
long  as  the  orchard  remains,  it  is  well  to  study  from  year  to  year  the  way 
in  which  various  soil  treatments  influence  those  factors  determining  root 
distribution  and  then  employ  those  practices  that  lead  indirectly  toward 
ideal  root  systems.  Orchards  do  not  die  out  or  become  unprofitable  only 
because  of  fungi,  bacteria,  summer  drought  or  winter  cold.  These  are 
always  possible  contributing  factors  and  often  determining  factors,  but 
in  many  cases  the  fundamental  cause  of  distress  is  a  root  system  inade- 
quate for  requirements  of  the  tree  in  an  emergency — inadequate  perhaps 
because  too  shallow,  or  in  too  severe  competition  with  the  roots  of  other 
plants  or  because  it  is  not  exploiting  enough  soil.  Sometimes,  though 
the  contributing  causes  to  the  death  or  failure  of  the  trees  may  be  un- 
avoidable, the  fundamental  factor  may  be  completely  under  control. 

Summary. — In  terms  of  response  to  gravity  and  the  evaporating 
power  of  the  air,  soil  moisture  may  be  classified  as  gravitational  or  free, 
capillary  and  hygroscopic.  Only  the  capillary  moisture  is  available  to  the 
plant  in  any  considerable  amount.     The  capillary  supply  is  derived  from 


SOIL  MOISTURE  65 

precipitation  and  irrigation  or  to  a  limited  extent  from  the  gravitational 
water  that  reaches  the  ground  water  level.  The  optimum  water  content 
for  the  growth  of  plants  is  reached  when  its  relative  saturation  is  approxi- 
mately 50  per  cent.  A  certain  percentage  of  the  soil  moisture  is  held  in  a 
capillary  adsorbed  or  colloidal  form  and  is  not  frozen  at  the  ordinary 
freezing  point  of  water.  This  portion  of  the  water  supply  is  of  great 
importance  to  the  plant.  The  evidence  indicates  that  a  part  of  the  water 
of  plant  tissues  is  held  in  a  similar  manner  and  that  this  moisture  is 
significant  in  determining  drought  and  frost  resistant  qualities  of  the 
tissue  in  question.  The  percentage  of  the  rainfall  that  percolates 
beyond  the  range  of  the  tree  roots  varies  greatly  with  many  factors,  total 
precipitation  being  one  of  the  most  important.  Comparatively  little 
water  that  percolates  beyond  the  range  of  the  roots  becomes  available 
for  later  use  through  capillary  rise.  The  lateral  movement  of  soil 
moisture  depends  principally  upon  soil  texture  and  the  method  by  which 
irrigation  water  is  applied  to  the  soil  should  be  determined  accordingly. 
Root  distribution  is  governed  first  of  all  by  the  growth  characteristic 
of  the  species  or  variety  in  question.  To  an  important  extent,  however, 
it  is  influenced  by  soil  conditions,  particularly  soil  moisture  and  soil 
aeration.  A  deep,  moderately  wide-ranging  root  system  is  preferable  to 
one  that  is  shallow,  wide  spreading  or  narrow.  Though  the  great  major- 
ity of  the  roots  of  most  orchard  trees  are  in  the  upper  foot  or  fifteen  inches 
of  soil,  there  is  little  evidence  that  ordinary  tillage  results  in  an  injurious 
root  pruning.  Shallow  soils,  soils  underlaid  by  hardpan  or  with  a  high 
water  table,  should  be  avoided  for  fruit  culture  because  of  the  restricted 
root  range  that  they  necessitate  and  the  consequent  susceptibility  to 
drought  injury  of  one  kind  or  another.  Depth  of  rooting  can  be  con- 
trolled to  a  considerable  extent  by  cultural  practices,  such  as  tillage,  the 
use  of  cover  crops  or  intercrops  of  different  kinds,  irrigation  and  drainage. 


CHAPTER  V 

THE  RESPONSE  OF  FRUIT  PLANTS  TO  VARYING  CONDITIONS 
OF  SOIL  MOISTURE  AND  HUMIDITY 

Water  as  a  factor  in  growth  thus  far  has  been  discussed  only  in  its 
general  importance  in  the  development  of  the  plant  as  a  whole.  There 
are,  in  addition,  certain  specific  responses  made  by  the  plant  to  a  varying 
water  supply. 

Influence  of  Soil  Moisture  on  Vegetative  Growth. — One  of  the  most 
important  of  these  specific  responses  is  in  new  tissue  formation,  an  in- 
crease in  size  or  bulk.  Data  have  been  presented  in  Table  19  showing 
the  influence  that  various  methods  of  culture,  such  as  tillage,  tillage  and 
cover  crops  and  artificial  mulches,  have  upon  vegetative  growth  measured 
by  trunk  circumference. 

New  Shoots  and  Their  Leaves. — Table  33  gives  certain  averages  found 
by  Hedrick  in  sod-mulched  and  cultivated  plots  in  a  New  York  apple 
orchard.  Every  phase  of  vegetative  growth  measured  showed  a  gain 
from  tillage.  Moreover  the  tillage  plot  averaged  considerably  higher 
in  moisture  during  the  growing  season.  Probably  much  of  the  influence 
of  tiflage  was  due  to  the  increased  moisture  available  in  the  soil,  yet  it  is 
difficult  to  say  how  much  is  to  be  attributed  to  this  factor  and  how  much 
to  the  influence  of  the  tillage  on  plant  nutrients,  particularly  nitrates. 


Table    33.— Influence    of    Tillage    Methods    Upon    Vegetative 

Apples^^ 

Growth    in 

Sod 

Cultivated 

Avprnorp  IpTurfVi  nf  npw  Int.prals  in  infihpf?                              

3.40 
1.90 
0.87 
1.10 

6.70 

Average  number  of  new  laterals  per  year                       

4.40 

Average  weight  of  leaves  in  grams                                 

1.15 

Average  gain  in  trunk  diameter  in  inches  in  4  years 

2.10 

More  direct  evidence  of  the  effect  of  water  on  vegetative  growth  is 
furnished  by  certain  orchard  irrigation  experiments.  The  following 
quotations  from  a  report  on  an  investigation  in  Utah  bear  on  this  point. 
"Frequent  applications  of  irrigation  water  applied  to  peaches  on  a 
gravel  loam  (about  15  feet  deep)  at  intervals  of  7  or  8  days  produced  a 
more  continuous  and  greater  total  twig  growth  than  the  same  total 
amount  of  water  applied  with  larger  applications  at  intervals  of  every 
10  to  12  days.     The  more  porous  the  soil  the  more  frequently  the  trees 

66 


RESPONSE  OF  FRUIT  PLANTS  TO  CONDITIONS  OF  SOIL 


67 


should  be  watered.  .  .  ,  With  varying  times  of  application  of  irrigation 
water  the  season  of  most  rapid  twig  growth  is  during  the  season  of 
watering."'^  Barss,^  reporting  upon  the  results  of  some  pot  irrigation 
experiments  with  pears,  states:  "The  most  noticeable  variation  in 
response  to  the  application  of  different  amounts  of  water,  was  found  in  the 
development  of  the  new  wood.  All  the  lots  started  vegetative  growth  at 
about  the  same  time  .  .  .  but  terminal  bud  formation  took  place  early 
on  the  poorly  watered  trees  and  much  later  on  the  trees  of  the  other  lots. 
Furthermore  there  were  great  differences  in  the  rate  of  wood  growth  in 
these  different  lots  while  they  were  actually  growing.  .  .  .  The  spurs 
on  the  better-watered  trees  were  larger  and  more  vigorous.  .  .  .  From 
leaf  samples,  collected  and  weighed  in  order  to  bring  out  any  existing 
differences  in  weight,  it  is  apparent  that,  on  the  average,  the  leaves 
in  the  lots  receiving  most  water  were  far  heavier  than  those  in  the  lots 
receiving  less  water."  He  also  found  the  leaves  on  the  trees  receiving  the 
smallest  water  supply  were  variable  in  both  size  and  shape,  their  petioles 
were  slender,  their  lower  surfaces  were  markedly  pubescent  and  their 
color  was  dark  green.  Callus  tissue  formed  much  more  frequently  on  the 
well  watered  trees. 

An7iual  Rings  and  Trunk  Circumference. — The  results  of  study  on  the 
relation  between  tree  growth  and  total  yearly  rainfall  in  Arizona  are 


1870  1880  1890  1900  l^iQ 

Fig.  8. — Actual  rainfall  compared  with  rainfall  calculated  from  growth  of  trees, 
Arizona.  Solid  line  equals  calculated  rainfall.  Broken  line  equals  observed  rainfall. 
{After  Douglass J^) 

interesting  in  this  connection.  Under  the  comparatively  arid  conditions 
of  that  region  the  correlation  between  the  two  was  found  to  be  so  close 
that  with  a  knowledge  of  the  total  rainfall  of  any  one  year  the  average 
increase  in  diameter  of  trees  could  be  estimated  with  an  average  accuracy 
of  82  per  cent.;  conversely,  knowing  the  average  diameter  increment 
of  a  small  group  of  forest  trees  for  any  one  year  it  was  possible  to  estimate 
with  equal  accuracy  the  total  precipitation  of  that  year.  Figure  8  shows 
graphically  the  closeness  of  this  correlation.  Huntington^^  employed 
this  method  of  estimating  annual  rainfall  for  the  study  of  climatic  varia- 
tions during  the  last  1,000  years,  obtaining  growth  records  from  the  giant 
Sequoias  of  California.  Hartig,^^  however,  found  that  in  parts  of 
Germany  where  low  moisture  content  of  the  soil  apparently  is  not  the 
limiting  factor  to  growth,  the  beech  makes  a  smaller  annual  ring  during 


68 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


seasons  that  are  cold  and  wet  than  during  years  of  more  nearly  average 
temperature  and  humidity.  The  decreased  growth  during  the  wet 
season  may  be  correlated  with  poorer  aeration  in  the  soil. 

Moisture  Supply  and  the  Growth  Period  in  Early  Spring. — Most 
deciduous  fruits  have  a  short  period  of  very  rapid  vegetative  growth  in  the 
spring,  followed  by  a  longer  period  of  comparatively  slow  growth  that 
precedes  the  resting  stage.  That  this  is  a  characteristic  of  most  deciduous 
woody  plants  is  brought  out  by  data  condensed  in  Table  34.  Of  the 
70  species  of  trees,  shrubs  and  vines  considered  hardy  enough  for  outdoor 
culture  in  central  Michigan  approximately  one-fourth  had  completed 
their  shoot  growth  and  formed  their  terminal  buds  by  June  1,  and  over 
two-thirds  had  reached  a  similar  stage  by  June  20.  In  no  case  was  there 
appreciable  shoot  growth  before  May   1.     Gourley^^   states  that  this 


Table  34. — Numbers  of  Trees,  Shrubs  and  Vines  Completing  Shoot  Growth 
AT  Different  Dates 

(After  Baileif) 


Date   of  terminal  bud   formation 

June  1  or 
earlier 

June  1  to 
10 

June  10  to 
20 

June  20  to 
July   1 

July  1  to 
15 

After  July 
15 

Number                         .... 

16 
23 

8 
11 

24 
34 

14 
20 

5 

7 

3 

Per  cent 

4 

period  of  rapid  growth  in  the  apple  lasts  only  about  25  days  in  New 
Hampshire  and  that  it  is  during  this  period  that  external  factors,  such 
as  moisture,  have  their  greatest  influence  upon  new  tissue  formation. 
In  his  work  approximately  43,000  measurements  were  taken  and  his 
data  point  to  the  conclusion  that  there  was  no  very  close  correlation 
between  the  humidity  and  rainfall  curves  and  the  growth  curve  during 
this  period,  though  it  was  not  possible  to  control  all  factors  under  field 
conditions.  The  growth  curve  showed  a  closer  correlation  with  tem- 
perature than  with  any  other  factors  studied.  In  Idaho,  irrigation  of 
apple  trees  after  July  15  had  no  effect  upon  shoot  growth  but  as  a  rule 
the  more  irrigation  water  applied  before  July  1,  the  greater  was  the  shoot 
growth. ^2*  A  similar  correlation  between  growth  and  soil  moisture 
during  the  months  of  May,  June  and  July  has  been  observed  in  Indiana^^^ 
and  it  was  in  the  plots  with  the  lowest  water  content  that  there  was  the 
closest  correlation  between  growth  and  soil  moisture.  With  moisture 
conditions  approaching  the  optimum,  an  increased  rainfall  or  surplus  irri- 
gation water  has  comparatively  little  influence  in  forcing  growth. 

Pearson^^^  h^s  made  a  valuable  contribution  to  the  knowledge  of 
the  importance  of  an  adequate  soil  moisture  supply  during  the  com- 


RESPONSE  OF  FRUIT  PLANTS  TO  CONDITIONS  OF  SOIL 


69 


paratively  short  period  of  rapid  vegetative  growth.  Figure  9  presents 
graphically  the  results  of  his  series  of  observations  upon  yellow  pine 
seedlings  near  Flagstaff,  Arizona. 

In  commenting  upon  the  data  presented  in  this  figure  he  says:  "Contrary 
to  what  might  be  expected,  there  is  no  apparent  relation  between  height  growth 
and  annual  precipitation,  summer  precipitation  or  winter  precipitation,  m  fact, 
the  growth  from  year  to  year  often  varies  inversely  with  the  precipitation  for 
any  of  these  periods.  When  it  is  considered  that  of  the  total  annual  precipi- 
tation at  Fort  Valley,  the  mean  amounting  to  about  23  inches,  approximately  40 
per  cent,  comes  during  the  winter  months  (December  to  March),  30  per  cent, 
during  July  and  August,  and  less  than  10  per  cent,  during  the  spring  months 
(April  and  May),  the  foregoing  statements  are  startling.  In  order  to  clarify  the 
problem,  it  is  necessary  to  analyze  the  growth  habits  of  Western  yellow  pine  as 
well  as  the  cUmatic  and  soil  conditions  under  which  it  grows  in  this  locality. 


■ 

y' 

\ 

/ 

\ 

/ 

\ 

1 

\ 

/ 

\ 

\ 

1 

S 



""■^-^ 

/ 

\ 

1 

/ 

\ 

V 

/ 

\ 

\ 

/ 

\ 

^^ 

>. 

.-^ 

~>vv 

X 

"> 

Nr--r" 

/. 

> 

^?\ 





^... 

'^ 

'^^^v^ 

A 

/ 

^ 

/ 

\ 

/ 

-e-- 



,^^ 

.^^" 

\ 

1915 


1916      1917 


1909    1910       1911        1912       1913 

Year 

Fig.  9. — Seasonal  precipitation  and  annual  height  growth  of  western  yellow  pine 
saplings  from  1909  to  1917.  a,  Annual  precipitation;  h.  Winter  precipitation  (December- 
March  preceding  the  corresponding  year's  growth) ;  c,  Summer  (July-August)  precipita- 
tion; d,  Annual  height  growth;  e,  Spring  (April-May)  precipitation.      {After  Pearson y^"^) 


The  terminal  shoots  begin  to  elongate  about  the  middle  of  May,  and  by  July  1 
they  have  practically  completed  their  growth.  Thus  it  appears  that  the  entire 
height  growth  occurs  during  the  period  of  lowest  precipitation  of  the  year.  From 
the  middle  of  May  to  the  middle  of  July  the  rainfall  is  normally  less  than  one  half 
inch,  and  comes  in  such  small  showers  as  to  be  of  no  benefit  to  deep-rooted  plants. 
It  is  evident,therefore,that  the  moisture  utihzed  in  making  this  growth  is  drawn 
almost  entirely  from  a  stored  supply.  It  is  also  evident  that  the  midsummer 
rainfall,  since  it  does  not  begin  until  July,  when  height  growth  has  practically 
ceased,  is  of  httle  or  no  consequence,  as  far  as  the  current  year's  height  growth  is 
concerned.  The  water  storage  which  makes  growth  possible  is  mainly  the 
result  of  the  preceding  winter's  precipitation;  but  it  is  the  supplementary  sup- 
ply in  April  and  May  which  determines  whether  the  growth  is  to  be  above  or 


70  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

below  normal.  ...  It  is  evident  from  the  precipitation  figures  for  1913  that 
the  pines  in  that  year  depended  entirely  upon  winter  precipitation  for  their  height 
growth.  Since  the  total  precipitation  in  April,  May,  and  June  was  only  0.25 
inch,  it  may  be  readily  seen  that  an  addition  of  2  or  3  inches  during  this  period 
would  have  resulted  in  an  appreciable  increase  in  soil  moisture  and  presumably 
in  height  growth.  Such  was  the  case  in  1914  and  in  a  more  marked  degree  in  1915 
and  1917.  If,  as  is  often  the  case,  the  first  of  April  marks  the  end  of  the  season's 
storms,  a  dry  period  of  3  months  prior  to  the  beginning  of  the  summer  rains  may 
be  expected.  Since  yellow  pine,  on  account  of  the  low  temperature,  does  not 
begin  growth  until  about  the  middle  of  May,  a  dry  period  of  6  weeks  intervenes 
between  the  last  storm  or  the  disappearance  of  snow  and  the  beginning  of  growth. 
During  this  period  a  large  portion  of  the  stored  moisture  supply  is  dissipated 
without  benefit  to  the  tree.  If,  on  the  other  hand,  belated  storms  continue 
through  April  and  into  May,  the  stored  water  supply  is  not  only  conserved,  but 
may  be  actually  augmented.  A  typical  example  of  the  first  type  of  spring  was  in 
1916.  Despite  a  winter  precipitation  of  over  16  inches,  the  highest  on  record  in 
9  years,  soil  moisture  conditions,  after  it  became  warm  enough  for  growth,  were 
decidedly  below  normal.  .  .  .  The  years  1915  and  1917  are  examples  of  the 
second  type  of  spring.  The  winter  precipitation  was  only  9.4  inches  in  1914-15 
and  6.1  inches  in  1916-17,  but  in  both  years  the  precipitation  between  April 
1  and  May  15  was  around  6  inches." 

The  '^Second  Growth"  of  Midsummer  or  Late  Summer. — A  second 
period  of  rapid  vegetative  growth  frequently  occurs  in  late  summer  or 
fall.  Usually  it  takes  place  after  terminal  bud  formation  on  both  spurs 
and  shoots  in  the  case  of  spur  bearing  species.  Sometimes  the  terminal 
buds  on  the  shoots  "break"  and  a  new  shoot  growth  is  pushed  out; 
sometimes  terminal  buds  on  many  of  the  spurs  "break"  and  a  secondary 
spur  growth  takes  place  and  sometimes  the  lateral  buds,  rather  than 
the  terminals,  initiate  this  new  shoot  growth.  In  some  instances  terminal 
bud  formation  has  not  yet  occurred  in  the  primary  shoots  of  the  season, 
though  growth  has  slowed  down  very  materially,  so  there  is  a  sudden 
flush  of  rapid  vegetative  development.  Occasionally  this  "second 
growth,"  as  it  is  generally  called,  is  as  extensive  in  amount  as  that  made 
early  in  the  season,  though  this  is  not  usually  the  case.  Without  doubt 
nutritive  conditions  within  the  plant  and  in  the  soil  have  something  to 
do  in  determining  "second  growth"  but  the  fact  that  it  occurs  almost 
invariably  after  heavy  rains  or  irrigation  following  a  drought,  leads  to 
the  conclusion  that  it  is  due  at  least  in  part  to  changed  moisture  con- 
ditions. It  is  to  be  regarded  as  a  phenomenon  likely  to  accompany  irregu- 
larity in  moisture  supply  late  in  the  season,  and  is  a  response  of  the 
plant  to  disturbed  moisture  relations.  This  second  growth  is  sometimes 
accompanied  by  fall  blooming  in  some  of  the  tree  fruits.  Without 
doubt  the  "flush"  of  certain  evergreen  plants  of  tropical  countries  is 
a  related  phenomenon.  It  sometimes  gives  rise  to  two  "annual"  rings 
in  one  season  in  the  trunks  and  limbs  of  trees  and  other  woody  plants. 


RESPONSE  OF  FRUIT  PLANTS  TO  CONDITIONS  OF  SOIL  71 

If  this  second  growth  comes  fairly  early  so  that  the  new  tissues  have 
time  to  harden  and  mature  properly  before  winter  freezing,  little  harm 
may  result,  but  often  when  it  comes  late  in  the  season  the  tissues  do  not 
mature  thoroughly  and  serious  winter  killing  or  winter  injury  follows. 
It  is  doubtful  if,  irrespective  of  susceptibility  to  winter  injury,  much 
"second  growth"  is  desirable  in  sections  with  more  or  less  severe  winter 
weather,  for  there  is  reason  to  believe  that  the  tissues  are  formed  at  the 
expense  of  stored  materials  that  could  be  used  perhaps  to  better 
advantage  the  following  spring  and  summer. 

Influence  of  Water  Supply  on  the  Development  of  Fruit. — The 
influence  of  soil  moisture  on  the  development  of  the  fruit  is  no  less 
important  than  its  influence  on  vegetative  growth. 

Size. — The  largest  fruits  are  found  on  the  best  watered  trees  and 
there  is  abundant  experimental  data  to  show  the  effect  of  soil  moisture 
upon  fruit  size.  Thus  Hedrick,^^  who  found  his  tillage  plots  to  contain 
more  soil  moisture  than  his  sod-mulch  plots  reports  the  average  weight 
of  apples  from  the  cultivated  trees  to  be  7.04  ounces  while  the  average 
weight  of  those  growing  in  sod  was  only  5.01  ounces.  This  difference 
of  40  per  cent,  was  presumably  due  mainly  to  the  difference  in  moisture 
supply  and  accounts  in  large  part  for  the  difference  in  yield  between 
the  two  plots,  which  averaged  36  barrels  per  acre. 

In  the  discussion  of  the  influence  of  soil  moisture  upon  vegetative 
growth  it  is  pointed  out  that  new  shoot  growth  and  new  leaves  are  made 
early  in  the  season  and  it  may  be  only  during  a  comparatively  short 
period  in  spring  and  early  summer  that  this  growth  is  influenced  in  amount 
by  soil  moisture.  On  the  other  hand,  most  of  the  growth  of  the  fruit 
tissues  takes  place  after  midseason  and  therefore  it  is  reasonable 
to  believe  that  soil  moisture  exerts  its  greatest  influence  on  their 
development  during  the  last  half  of  the  summer  and  during  the  autumn. 
That  this  is  actually  the  case  is  indicated  clearly  by  a  number  of  irriga- 
tion experiments.  In  Idaho,  irrigation  of  winter  apples  before  July  10 
had  very  little  influence  on  their  size,  though  irrigation  after  that  date 
had  a  very  decided  influence. ^^^  Batchelor^^  in  reporting  upon  the 
results  of  irrigation  experiments  with  peaches,  states:  "No  amount  of 
water  applied  early  in  the  season  to  a  crop  of  peaches  on  a  gravelly  soil 
will  compensate  for  the  lack  of  water  during  the  month  before  harvest. 
...  A  larger  amount  of  water  is  evidently  required  if  the  irrigation  is 
deferred  until  late  in  the  season  than  in  case  the  water  is  applied  throughout 
a  longer  period  of  growth."  There  is  ample  evidence  to  show  that  for 
the  production  of  fruits  of  large  size  the  trees  should  be  well  supplied 
with  available  soil  moisture  throughout  their  growing  season.  Through 
measurements  of  apples  made  at  intervals  of  two  weeks  throughout  the 
season  it  has  been  found  that  size  increased  steadily  from  the  time  of 
setting  to  maturity.  ^^^  This  suggests  the  advisability  of  cultural  treat- 
ments to  promote  a  steady  growth.     That  there  is  a  limit,  however, 


72  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

to  the  increase  in  fruit  size  that  can  be  effected  through  increased 
moisture  supply  is  shown  by  many  irrigation  experiments.  For  instance, 
with  peaches  on  a  deep  gravelly  loam  in  Utah,  it  was  found  that  31 
acre-inches  of  irrigation  water  gave  as  large  size  and  as  large  yields  as 
62  acre-inches  under  the  same  conditions. ^^ 

An  interesting  moisture  relation  within  the  plant  itself  that  often 
affects  fruit  size  is  pointed  out  by  Chandler. ^^  He  shows  that  the  con- 
centration of  the  sap  within  the  leaves  of  the  tree  is  higher  than  that 
within  its  developing  fruits.  Consequently  in  times  of  drought,  when 
the  roots  are  unable  to  supply  the  amounts  transpired,  the  leaves  actually 
can  withdraw  moisture  from  the  fruits,  even  to  the  point  of  causing 
wilting  while  the  leaves  themselves  remain  turgid.  This  not  only  checks 
temporarily  all  increase  in  fruit  size  but  may  result  in  a  reduction.  Chan- 
dler cites  several  instances  in  which,  under  these  extreme  conditions, 
more  disastrous  results  occurred  in  cultivated  than  in  uncultivated 
orchards.  Cultivation  had  been  given  largely  for  the  purpose  of  con- 
serving moisture;  nevertheless  toward  the  end  of  a  long  drought  when 
the  moisture  supply  of  both  cultivated  and  uncultivated  orchards  was 
approaching  the  wilting  coefficient,  the  trees  in  the  cultivated  orchard 
suffered  more  because  they  had  larger  leaf  systems  and  required  more 
water  to  support  them.  Had  summer  pruning  to  reduce  the  leaf  systems 
been  done  promptly  in  these  cases,  evaporation  would  have  been 
reduced  and  wilting  of  the  fruit  prevented.  Chandler  states,  however, 
that  summer  pruning  for  the  purpose  of  increasing  fruit  size  through 
reducing  leaf  area  has  not  been  successful. 

Yield. — The  increases  in  yield  from  an  increased  moisture  supply,  up  to 
the  optimum,  are  in  general  still  more  striking  than  the  increases  in  size 
because  of  the  indirect  effects  of  moisture  through  better  fruit  setting 
and  the  formation  of  more  fruit  buds. 

A  striking  illustration  of  the  influence  of  rainfall  upon  yield  is  recorded 
for  the  palm  oil  tree  (Elaeis  guineensis)  in  the  British  Colony  of  Lagos. 
Data  showing  the  yearly  rainfall  and  the  yearly  exports  of  palm  oil  and  of 
palm  kernels  are  condensed  in  Table  35.  The  following  quotation  fur- 
nishes comment  on  these  data: 

"The  yield  of  fruit  from  the  palm  oil  tree  (Elaeis  guineensis)  varies  according 
to  rainfall.  With  a  sufficiency  of  moisture  the  tree  flowers  every  five  or  six  weeks, 
and  bears  eight  or  nine  mature  bunches  of  fruit  in  the  year,  but  if  the  rain  supply 
is  scanty  the  tree  flowers  only  every  ninth  or  tenth  week,  and  the  annual  yield 
is  reduced  to  about  five  bunches.  In  normal  times  the  Elaeis  bears  eight  heads 
(so-called  nuts)  in  the  year,  but  it  follows  a  similar  habit  to  the  cocoanut,  the 
heads  being  formed  spirally  in  the  axils  of  the  leaves  at  regular  intervals,  which 
are  long  or  short,  according  as  the  season  is  favorable.  The  mischief  arising  from 
insufficient  rainfall  does  not  finish  with  the  number  of  heads,  for  the  oil  is 
extracted  from  the  fiber  of  the  thin  outside  layers  of  the  fruit,  which  are  either 


RESPONSE  OF  FRUIT  PLANTS  TO  CONDITIONS  OF  SOIL  73 

Table  35. — Yearly  Rainfall  and  Exports  op  Palm  Oil  from  Lagos'" 


Year 

Rainfall, 

Palm  oil, 

Palm  kernels. 

inches 

gallons 

tons 

1887 

70.80 
49.87 

1888 

2,446,705 

42,525 

1889 

61.61 

3,349,011 

32,715 

1890 

90.88 

3,200,824 

38,829 

1891 

64.26 

4,204,835 

42,342 

1892 

69.68 

2,458,260 

32,180 

1893 

82,55 

4,073,055 

51,456 

1894 

70.10 

3,393,533 

53,534 

1895 

80.62 

3,826,392 

46,501 

1896 

74.23 

3,154,333 

47,649 

1897 

51.10 

1,858,968 

41,299 

1898 

80.20 

1,889,939 

42,775 

1899 

83.46 

3,292,881 

49,501 

1900 

72.82 

2,977,926 

48,514 

1901 

112.59 

3,304,055 

57,176 

1902 

47.82 

5,240,137 

75,416 

•    1903 

70.08 

3,174,060 

63,568 

red,  ripe,  succulent  and  rich  with  oil,  or  starved,  yellow,  and  destitute  wholly  or 
partially  of  oil,  according  to  the  amount  of  moisture  afforded  to  the  tree  during 
the  time  the  fruit  has  been  maturing,  "^o  Three  things  are  of  particular  interest 
in  connection  with  the  behavior  of  the  palm  oil  tree  in  Lagos:  (1)  Moisture  affects 
yield  mainly  through  influencing  the  frequency  of  flowering  and  fruiting.  (2) 
The  chemical  composition  of  the  fruit  is  greatly  modified.  (3)  Variations  in 
rainfall  are  as  likely  to  influence  fruit  production  the  succeeding  season  as  during 
the  current  j^ear.  This  is  explained  by  the  existence  of  two  seasons  of  heavy 
rainfall — one  early  and  one  late.  If  the  excess  or  the  deficiency  is  mainly  in  the 
latter  period,  its  influence  is  more  evident  in  production  the  following  calendar 
year.  More  attention  is  devoted  to  this  phase  of  the  question  under  Residual 
Effects  of  Soil  Moisture. 

Shape  and  Color. — The  influence  of  soil  moisture  on  the  color  and 
shape  of  fruit  is  of  little  importance  relatively  but  it  is  none  the  less  of 
interest.  In  Oregon  it  was  found  that  with  the  use  of  increasing  amounts 
of  irrigation  water  apples  tended  to  become  more  angular  and  elongated^^ 
and  the  same  phenomenon  has  been  noted  in  irrigated  orchards  in  Idaho. ^^4 
Many  observations  have  indicated  that  apples  in  a  very  dry  soil  are 
flatter  than  those  of  the  same  variety  grown  near  by  but  in  a  somewhat 
better  watered  medium.  In  irrigation  experiments  with  peaches  in 
Utah,  poor  color  was  associated  with  a  small  amount  of  water  and  high 
coloration  with  abundant  and  particularly  with  late,  watering.^^  A 
brighter  red  color  was  found  on  Esopus  apples  that  were  well  irrigated,  as 
compared  with  a  darker  and  duller  red  on  fruit  of  the  unirrigated  or 


74  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

lightly  irrigated  plots  in  Oregon.  ^^  Barss^  observes  that  Bartlett  pears 
from  trees  well  supplied  with  moisture  are  a  clear  green  at  picking  time; 
those  from  trees  suffering  for  lack  of  moisture  he  describes  as  bluish-gray 
green.  Increased  moisture  may  lead  indirectly  to  poorer  color  of  varieties 
of  apples,  pears  and  peaches  that  have  more  or  less  red  coloring  matter 
in  their  skin  by  producing  a  larger  wood  and  leaf  growth  and  thus 
more  shade,  the  formation  of  the  red  pigment  in  these  cases  being  depen- 
dent upon  sunlight  reaching  the  fruit  itself.  Though  this  effect  of  soil 
moisture  is  noted  only  late  in  the  season  as  the  fruit  is  maturing,  it  is 
not  an  effect  of  surplus  moisture  at  that  time  or  just  previous,  but  is 
rather  to  be  attributed  to  surplus  moisture  during  the  spring  months 
when  most  of  the  shoots  and  leaves  are  developed.  Thus  trees  with 
fruits  showing  the  effects  of  drought  in  poor  size  and  quality  may  at  the 
same  time  show  the  effects  of  too  much  moisture  during  the  spring  months 
in  poor  color.  Such  a  condition  suggests  the  contrasting  extreme,  namely 
high  color  from  good  exposure  to  the  light  incident  to  proper  foliage  and 
shoot  development  early  in  the  season  and  good  size  and  quality  incident 
to  abundant  moisture  late  in  the  season.  Either  extreme  can  be  produced 
or  at  least  approximated  by  skillful  culture,  particularly  in  irrigated 
sections  where  water  supply  is  under  control. 

Composition. — That  the  composition  of  fruit  is  influenced  materially 
by  water  supply  is  suggested  by  the  large  percentage  of  water  in  the 
tissues  of  the  fruit.  It  is  probable,  however,  that  the  most  important 
influence  of  soil  moisture  upon  quality  and  composition  is  not  in  modi- 
fying its  water  content,  but  rather  in  its  effect  upon  other  constituents. 
Thus  the  poor  quality  of  strawberries  ripening  during  or  immediately 
after  a  rainy  period  is  due  more  to  a  low  sugar  than  to  a  high  water  con- 
tent. Exact  figures  are  not  available  to  show  how  chemical  composition 
of  fruits  varies  with  definite  changes  or  variations  in  soil  moisture,  con- 
ditions being  otherwise  the  same,  but  it  is  presumable  that  such  figures 
would  show  material  differences.  Developing  oranges  may  contain  25  to 
30  per  cent,  less  moisture  during  the  middle  of  the  day,  when  transpi- 
ration is  at  its  highest,  than  at  night  when  it  is  at  its  minimum, ^^  but  the 
moisture  content  of  apple  leaves  has  been  found  to  vary  only  from  62.8 
per  cent,  to  64.8  per  cent,  when  the  soil  moisture  in  the  plots  in  which  the 
trees  were  growing  ranged  from  11  to  24  per  cent.^^^  This  suggests  that 
such  extreme  variations  as  have  been  found  in  the  orange  are  only  tempo- 
rary and  that  the  plant  possesses  a  marked  ability  to  construct  its 
tissues  along  a  chemical  pattern  independent  of  available  soil  moisture 
to  a  considerable  degree.  However,  comparatively  slight  differences  in 
chemical  composition  are  often  responsible  for  large  differences  in  flavor 
or  quality.  In  addition,  differences  in  soil  moisture  may  cause  shght 
differences  in  texture  and  in  the  size  and  cohesion  of  individual  cells  or 
groups  of  cells,  resulting  in  great  differences  in  quality.     The  comparative 


RESPONSE  OF  FRUIT  PLANTS  TO  CONDITIONS  OF  SOIL  75 

crispness  of  fruit  grown  where  there  is  an  abundance  of  soil  moisture  is 
a  matter  of  common  knowledge.  Bartlett  pears  grown  with  an  extremely 
limited  water  supply  are  distinctly  and  unpleasantly  astringent,  though 
fruit  of  that  variety  under  usual  conditions  is  without  astringency.^ 
Peaches  supplied  early  with  abundant  irrigation  water  but  suffering 
because  of  its  lack  late  in  the  season,  may  be  especially  sweet  and  of 
high  quality  but  somewhat  shriveled  and  of  little  commercial  value.^^ 

Many  claims  are  made  for  and  against  fruits  grown  in  irrigated 
sections.  The  discussion  is  based  on  the  assumption  that  there  is  some 
more  or  less  direct  influence  of  irrigation  water  on  the  composition  and 
consequently  on  flavor  and  quality.  If  this  were  the  case  the  evidence 
would  not  be  conclusive,  for  fruit  raised  either  in  an  irrigated  or  in  an 
unirrigated  section  is  a  product  of  the  many  factors  constituting  environ- 
ment and  not  solely  of  differences  in  soil  moisture.  Chemical  analyses 
of  many  hundreds  of  fruits  of  different  kinds  grown  with  and  without 
the  use  of  irrigation  water,  have  led  to  the  conclusion  that  in  most  decidu- 
ous fruits  differences  between  those  irrigated  and  those  not  irrigated  are 
negligible.''^  Onl}^  in  the  strawberry  were  important  differences  found. 
In  that  fruit  the  irrigated  berries  were  lower  in  dry  matter,  sugar,  acid 
and  crude  protein  and  these  differences  were  accompanied  by  a  marked 
difference  in  keeping  quality.  There  appears  to  be  little  reason  for  the 
popular  belief  that  irrigated  fruits  as  a  rule  are  softer  and  more  watery 
than  those  not  irrigated.  It  seems  to  make  no  difference  whether  the 
soil  receives  its  water  from  rains  or  through  an  irrigation  flume. 

Disease  Resistance  and  Susceptibility. — Correlated  with  the  influence 
of  soil  moisture  on  the  texture  and  composition  of  the  tissues  of  shoot, 
leaf  and  fruit  is  its  influence  on  resistance  and  susceptibility  to  certain 
diseases.  This  has  been  noted  many  times  in  the  common  bacterial 
fireblight  of  apples  and  pears.  This  disease  works  much  more  freely  in 
soft  succulent  tissues,  slowing  up  or  ceasing  entirely  as  it  reaches  older 
and  harder  wood.  Thus  high  moisture  content  of  the  soil,  forcing  a  more 
succulent  and  vigorous  growth,  favors  the  development  of  the  disease 
and  there  are  sections  where  the  most  practicable  method  of  controlling 
it  on  certain  varieties  is  such  culture  as  will  maintain  the  soil  moisture 
at  a  point  somewhat  below  the  optimum  for  growth  though  well  above 
the  wilting  coefficient.  An  investigation  of  the  relation  between  water 
content  of  soil  and  the  prevalence  of  fireblight  in  Idaho  showed  that 
the  soil  moisture  averaged  3  to  8  per  cent,  higher  in  badly  blighted 
orchards  than  in  nearby  orchards  having  little  of  the  disease. ^^4  Similar 
differences  were  found  in  the  soil  moisture  content  of  slightly  blighted 
and  badly  blighted  parts  of  the  same  orchard  and  in  the  soil  under 
diseased  and  disease-free  trees.  Extreme  atmospheric  humidity  may 
occasionally  be  a  contributing  factor.  Presumably  soil  moisture  exerts 
equally  great  influence  on  susceptibihty  or  resistance  to  many  other 


76  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

bacterial  and  fungous  diseases.  A  series  of  dry  seasons  is  almost  certain 
to  be  accompanied  by  an  increase  in  the  virulence  of  the  Illinois  blister 
canker  in  those  regions  where  that  disease  is  prevalent. ^^  The  influence 
of  soil  moisture  on  certain  physiological  disturbances  is  discussed  later. 

Residual  Effects  of  Soil  Moisture. — The  influence  of  precipitation  or 
of  irrigation  early  during  the  growing  season  is  more  or  less  immediate. 
On  the  other  hand  water  falling  or  applied  late  during  the  growing  season 
may  have  less  of  an  immediate  effect  on  the  plant  and  a  correspondingly 
greater  effect  at  a  later  period,  or  even  the  following  year.  Particularly 
is  this  true  of  late  fall  or  early  winter  rains  or  irrigation.  This  is  due 
partly  to  the  fact  that  some  of  the  water  is  stored  in  the  soil  for  later  use 
and  partly  to  the  fact  that  the  benefit  that  the  plant  derives  from  absorb- 
ing some  of  it  immediately  may  not  be  apparent  until  considerably  later. 
It  is  thus  proper  to  speak  of  the  residual  effects  of  soil  moisture. 

On  Vegetative  Growth. — It  is  a  common  observation  that  trees  suffer- 
ing from  drought  in  late  summer  and  early  fall  shed  their  foliage  early. 
This  is  particularly  true  of  species  and  varieties  ripening  their  fruit 
comparatively  early.  The  function  of  the  foliage  during  late  summer 
and  fall  is  to  manufacture  food  materials  which,  for  the  most  part, 
are  stored  through  the  winter  for  use  in  tissue  building  in  the  spring.  A 
large  part  of  the  new  growth  (roots,  shoots,  leaves  and  flowers)  in  early 
spring  is  at  the  expense  of  stored  foods.  Premature  defoliation,  from 
drought  or  any  other  cause,  therefore,  is  likely  to  result  in  a  check  to 
growth  the  following  spring  through  cutting  down  the  available  reserves. 
Though  exact  experimental  data  in  support  of  this  line  of  reasoning  are 
not  available  there  is  abundant  circumstantial  evidence  and  the  record 
of  numerous  observations  is  very  suggestive. 

Whitten^^^  has  assembled  some  data  bearing  on  this  question  for  the 
years  1894-1898  (see  Table  36).  In  commenting  on  these  he  says:  "It  will  be 
observed  that  the  last  part  of  the  years  1894  and  1897  were  marked  by  severe 
drouths,  and  that  the  average  growth  of  uncultivated  trees  fell  off  to  a  marked 
degree  during  the  next  year  or  two  after  each  of  these  dry  seasons.  Where 
trees  were  well  cultivated,  to  conserve  the  moisture  in  the  soil,  this  falling  off  of 
growth  was  not  noticeable.  .  .  .  The  unfavorable  effects  of  drouth  upon 
uncultivated  trees  may  not  be  so  apparent  during  the  dry  year  itself  as  it  is  1  or 
even  2  years  later."  Though  unfortunately  data  are  not  available  as  to  the 
exact  moisture  content  of  the  soils  in  these  plots  during  the  5-year  period  in 
question,  there  is  little  doubt  about  soil  moisture  being  mainly  responsible  for  the 
differences  in  growth  recorded. 

On  Yields. — The  residual  effects  of  soil  moisture  are  not  limited  to 
vegetative  growth.  In  all  probability  they  have  rather  general  influence 
and  affect  yield.  This  is  indicated  by  investigation  of  the  olive  industry 
near  Sfax  in  Northern  Africa.''^ 


RESPONSE  OF  FRUIT  PLANTS  TO  CONDITIONS  OF  SOIL 


77 


Table  36. — Showing  Certain  Residual  Effects  of  Soil  Moisture 

(After  Whitten^^*) 


Growth  ( 

in  inches) 

Variety 

Age 

Kind  of  cultivation 

1895 

1896  1897 

1898 

Ben  Davis 

7 

17.6 

21.7 

23.2 

24.5  Clean  cultivation. 

Ben  Davis 

11 

12.1 

12.4 

16.6 

14. 5|  Clean  cultivation;  cover  crops. 

Ben  Davis 

14 

17.0 

9.5 

16.2  10.8  Seeded  to  clover. 

Jonathan 

9 

17.2 

9.3 

13.6 

11.0 

In  clover;  cultivated  under  each  tree. 

Jonathan 

10 

7.3 

6.6 

11.4 

9.6 

Clean  cultivation;  cover  crops. 

Genet 

30 

4  ?, 

6  1 

10  4 

6  6 

In  bluegrass  and  clover;  some  culti- 

vation around  each  tree. 

Genet 

30 

3.6 

5.5 

8.9 

4.4 

In  bluegrass  pasture. 

Genet 

14 

13.0 

9.3 

11.2 

7.4 

In  clover. 

Rainfall  in  Inches  During  the  Growing  Season  for  Each  of  the  5  Years 


Month 


1894    1895    1896    1897    1898 


2.02  I  1.04 

4.33  6.09 

3.04  5.78 

1.20  I  4.93 

1.29  I  2.30 

7.57  I  1.48 

October 0.98  i  0.25 


April .  . . 
May . .  . 
June. . . 
July... 
August . 
September . 


3.08 
5.61 
4.33 
3.79 
1.85 
3.61 
2.45 


4.83 
3.19 
6.59 
4.28 
1.89 
0.51 
0.69 


2.76 
8.39 
9.02 
4.60 
0.47 
5.43 
2.61 


The  following  quotation  illustrates  the  point : 

"Although  the  records  do  not  cover  a  sufficientlj^  long  period  to  establish  a 
definite  relation,  it  would  appear  that  there  is  some  connection  between  the  size 
of  the  crop  and  the  amount  of  rainfall  of  the  preceding  year  or  years,  but  not 
that  of  the  spring  preceding  the  ripening  of  the  crop.  Thus,  the  comparatively 
heavy  rainfall  (3.6  inches  above  the  normal)  in  1897  doubtless  had  something 
to  do  with  the  large  crop  of  1898,  although  the  total  rainfall  of  the  first  5  months 
of  the  latter  year  was  less  than  half  of  the  normal.  Again  in  1901,  when  the 
crop  was  less  than  half  the  average  of  9  years,  the  rainfall  for  the  first  5  months 
was  not  greatly  below  the  normal,  but  that  of  the  pre\aous  year  was  less  than  half 
the  normal,  and  during  the  3  years  previous  the  annual  rainfall  was  only  a  little 
more  than  half  the  normal.  It  is  noteworthy  that  in  1900,  after  2  years  of 
rainfall  much  below  the  normal,  the  crop  was  about  an  average  one.  This  was 
probably  due  to  the  heavy  rainfall  of  November,  1899,  which  was  more  than  three 
times  the  normal  for  that  month,  while  the  precipitation  during  the  first  5  months 
of  the  year  in  which  the  crop  was  made  was  less  than  40  per  cent,  of  the  normal." 

Still  further  evidence  is  fm-nished  by  a  report  on  the  relation  of 
certain  climatological  factors  to  fruit  production  in  California: 


78  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

"The  character  of  the  autumn,  particularly  with  reference  to  rainfall,  deter- 
mines in  large  measure  the  size  and  the  quahty  of  the  fruit  crop  of  the  following 
year.  An  interesting  example  of  this  relation  is  apparent  in  the  1919  deciduous 
fruit  crop,  which  is  the  largest  of  this  kind  ever  grown  in  California.  During 
September,  1918,  the  heaviest  rains  recorded  in  a  month  of  September  in  California 
during  69  years  of  record  were  general  throughout  the  central  portions  of  the 
State."ioi 

Regularity  of  bearing,  as  is  pointed  out  later,  is  probably  more  closely 
associated  with  and  dependent  upon,  natural  flowering  habit  and  the 
nutritive  conditions  within  the  plant  than  upon  soil  moisture.  However, 
the  following  quotation  from  a  report  on  a  series  of  orchard  soil  experi- 
ments in  Pennsylvania  suggests  the  wisdom  of  looking  after  the  moisture 
supply  when  it  is  more  or  less  under  control:  "In  two  treatments,  the 
yields  of  Baldwin  and  Spy  have  remained  almost  constantly  between 
400  and  700  bushels  per  acre  annually  for  the  past  7  years,  while  marked 
fluctuations  in  yield  were  occurring  in  adjacent  plots  under  other  treat- 
ments. The  essential  features  of  the  former  treatments  have  been 
an  ample  food  and  moisture  supply,  the  absence  of  excessive  yields  in 
any  one  year,  and  undisturbed  root  system. "^^^ 

In  most  of  the  cases  cited  it  is  impossible  to  differentiate  between  the 
direct  influence  upon  the  plant  of  water  from  the  rains  of  the  preceding 
summer  and  fall  stored  over  winter  in  the  soil  and  what  has  been  termed 
indirect  effects  through  immediately  influencing  leaf  fall  and  food  storage. 
To  the  grower  it  is  the  combined  effect  that  is  important.  The  facts 
presented  carry  a  particularly  significant  lesson  for  the  grower  in  an 
irrigated  section  where  fall  and  winter  rains  cannot  be  depended  on,  but 
irrigation  water  is  available.  They  suggest  also  that  the  tree  that 
matures  its  crop  early  in  the  season,  whether  a  cherry,  apricot,  peach  or 
summer  apple,  has  as  real,  though  perhaps  not  as  great  a  need  of  late 
summer,  fall  and  winter  irrigation  as  one  maturing  its  crop  in  October. 

Influence  of  Atmospheric  Moisture  on  Growth. — It  is  difficult  in 
many  cases  to  distinguish  clearly  between  the  effects  of  soil  moisture  and 
of  atmospheric  humidity  on  the  plant.  Atmospheric  humidity  has  an 
influence  on  plant  development  independent  and  distinct  from  that  of 
soil  moisture,  though  it  often  happens  that  both  influences  tend  in  the 
same  general  direction. 

In  General. — Under  average  outdoor  growing  conditions  abundant 
soil  moisture  is  likely  to  be  accompanied  by  relatively  high  humidity  and 
low  soil  moisture  by  a  dry  atmosphere.  In  practice,  therefore,  these  two 
factors  of  environment  are  more  or  less  interdependent.  The  relation  of 
the  two  is  brought  out  by  data  presented  in  Table  37.  In  a  general  way 
it  may  be  stated  that  extreme  moisture,  either  of  soil  or  of  air,  hinders 
the  differentiation  of  tissues  while  dryness  accentuates  the  develop- 
ment   of   strengthening   and    conducting   tissues.     Examples   of   these 


RESPONSE  OF  FRUIT  PLANTS  TO  CONDITIONS  OF  SOIL 


79 


Table  37. — The  Influence  of  Moist  and  Dry  Soil  and  Air  on  Size  of  Leaf 
OF  Tropaeoltjm  Majus 

_  (After  Kohl^^) 


Soil 

Air 

Relative  size  of 
leaf  blade 

Moist 
Moist 
Dry 
Dry 

Moist 
Dry 
Moist 
Dry 

5 

4 
3 

1 

results  are  to  be  found  in  aquatic  plants  on  the  one  hand  and  in  desert 
plants  on  the  other.  In  the  former  the  cuticle  is  usually  thin  and  per- 
meable, the  stomata  are  numerous  and  exposed,  frequently  the  surface 
of  the  epidermis  is  enlarged  and  woody  tissue,  sclerenchyma  and  col- 
lenchyma  are  poorly  developed.  In  xerophytic  plants,  growing  under 
very  dry  conditions,  the  cuticle  is  thickened  and  rendered  imperme- 
able by  waxy  impregnations;  the  surface  of  the  entire  plant  is  reduced  to  a 
minimum,  the  stomata  are  few  in  number  and  frequently  situated  at  the 
base  of  depressions  in  the  surface  of  the  leaf.  Wood  and  fibers  are 
developed  to  a  marked  degree  and  specially  differentiated  water  storage 
tissue  is  of  frequent  occurrence. 

Apparently  atmospheric  humidity,  rather  than  soil  moisture,  soil,  or  tempera- 
ture, is  the  factor  determining  the  limits  for  the  production  of  certain 
varieties  of  dates.  Those  of  the  Deglet  Noor  type  thrive  only  in  the  driest 
cUmates,  Hke  that  of  the  desert  oasis  with  a  mean  humidity  of  35  to  40  per  cent. 
Dates  of  a  different  type  are  grown  in  the  vicinity  of  Alexandria,  Egypt,  with  a 
mean  annual  humidity  of  68  per  cent.*^ 

Russeting  of  Fruit. — In  addition  to  the  more  general  influences  of 
atmospheric  humidity  and  soil  moisture  on  plant  development  there 
are  certain  more  or  less  specific  influences  on  fruits  and  fruit  plants. 
One  of  the  most  conspicuous  and  frequently  observed  is  the  effect  on  the 
russeting  of  the  skin  of  certain  pomaceous  fruits,  particularly  the  apple 
and  the  pear.  This  results  from  a  cracking  and  weathering  off  of  the 
epidermis  and  an  increased  development  of  the  corky  parenchyma 
beneath.  It  occm-s  especially  in  humid  climates  or  during  rainj^  sea- 
sons. For  instance  the  Bosc  and  Winter  Nelis  pears  as  grown  in  the  dry 
atmosphere  of  the  Rogue  River  valley  of  southern  Oregon  are  practi- 
cally smooth  skinned  fruits.  Grown  in  the  more  humid  Willamette 
valley  a  hundred  miles  farther  north  their  surface  is  almost  completely 
russeted.  The  Cox  Orange  apple  is  a  half  russet  variety  as  grown  in 
England;  it  is  a  smooth-skinned  fruit  as  grown  in  the  Okanogan  region  in 
British  Columbia.  The  fruit  trade  generally  considers  that  fruit  pro- 
duced in  irrigated  sections  has  a  higher  "finish"  than  fruit  of  the  same 


80  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

varieties  produced  in  non-irrigated  orchards.  The  reason  Kes  in  the 
lower  atmospheric  humidity  of  the  sections  where  irrigation  is  practiced 
and  is  in  no  way  directly  connected  with  the  irrigation. 

This  russeting  of  the  skin  is  often  attributed  to  the  action  of  certain  spray 
materials  and  without  doubt  is  sometimes  partly  or  even  entirely  caused  by 
them.  In  most  cases,  however,  atmospheric  humidity  is  an  important  contribut- 
ing factor.  The  following  quotation  from  a  report  by  Morse, ^^  who  has  made  a 
study  of  the  subject  particularly  as  it  relates  to  spray  injury,  is  instructive: 

"One  of  the  most  prominent  facts  shown  by  the  tabulated  results  of  1916  is 
the  relatively  high  per  cent,  of  russeted  fruit  on  each  plot,  even  on  the  un- 
sprayed  check  which  showed  20.57  per  cent.  This  duplicated  a  condition  which 
prevailed  in  1913  when  over  31  per  cent,  of  russeted  fruit  was  obtained  on  the 
plot  upon  which  no  insecticide  or  fungicide  was  applied,  and  the  different  sprays 
produced  a  corresponding  increase  in  amount.  Although  this  russeting  was 
materially  increased  by  different  sprays  it  is  evident  that  much  of  it  must  be 
attributed  to  natural  causes.  The  weather  conditions  of  1913  and  1916  were 
remarkably  similar  in  many  ways,  and  differed  from  previous  seasons  in  which 
abnormal  fruit  russeting  did  not  occur.  In  1913  the  first  spray  apphcation  was 
followed  by  a  month  of  unseasonably,  cold  weather,  with  frosts  and  cold,  north- 
west winds,  associated  with  much  cloudiness  and  heavy  rainfall.  In  1916, 
similar  conditions  prevailed  previous  to  and  following  the  first  application. 
This  was  also  followed  in  1916  by  heavy  rains  and  continuous  cloudy  weather 
in  June  after  the  second  application,  which  was  not  the  case  in  1913." 

In  extreme  cases  this  russeting  may  be  accompanied  by  cracking  and 
malformation  of  the  fruit,  resulting  in  considerable  loss.  Sorauer"^ 
notes  that  in  the  grape  similar  atmospheric  conditions  may  lead  to  the 
development  of  cork  pustules  on  the  peduncles  or  pedicels  as  well  as  on 
the  fruit.  The  cork  generally  starts  to  develop  under  the  stomata  and 
the  disorder  is  likely  to  make  its  initial  appearance  comparatively  early. 

Some  of  the  effects  of  high  humidity  previously  mentioned,  for 
example  increased  leaf  surface  and  the  russeting  of  fruit,  are  phenomena 
that  likewise  accompany  a  decreased  light  supply.  This  raises  the  ques- 
tion as  to  whether  a  part  of  the  apparent  direct  influence  of  atmospheric 
humidity  may  not  be  due  in  reality  to  its  action  in  intercepting  light. 

Fruit  Setting. — Inquiry  shows  that  atmospheric  humidity  is  often  of 
greater  importance  in  the  setting  of  fruit  than  is  generally  realized. 
Hot  drying  winds  at  blossoming  time  may  evaporate  the  moisture  from 
the  stigmatic  secretions  and  thus  prevent  the  germination  of  the  pollen. 
Extreme  atmospheric  humidity  may  interfere  with  the  work  of  insects 
in  carrying  pollen  or  it  may  encourage  the  development  of  certain  fungi 
such  as  brown  rot  and  apple  and  pear  scab  that  work  on  the  flowers  and 
destroy  or  injure  them.  The  well  known  effects  of  rain  during  the  blos- 
soming season  in  preventing  pollination,  in  washing  away  and  destroying 
pollen  and  in  diluting  stigmatic  secretions  may  be  mentioned.     A  study 


RESPONSE  OF  FRUIT  PLANTS  TO  CONDITIONS  OF  SOIL  81 

of  the  "June  drop"  of  the  Washington  Navel  orange  in  CaHfornia  indi- 
cates that  a  large  part  of  this  drop  is  due  to  abnormal  water  relations 
during  that  part  of  the  day  when  transpiration  is  at  its  highest. ^^ 

"During  the  day  the  fruits  (of  the  Washington  Navel  orange)  decrease  in 
water  content  as  much  as  25  to  30  per  cent.  It  has  been  definitely  established 
that  under  severe  conditions  when  the  atmospheric  pull  is  high  the  leaves  actually 
draw  water  back  out  of  the  young  fruits  to  maintain  themselves.  But  this  supply 
is  not  sufficient  and  they  decrease  in  moisture  content  also.  The  combined 
effect  of  this  tremendous  loss  from  leaves  and  fruits  results  in  tensions  in  the 
water-conducting  systems  of  the  tree.  These  tensions  as  well  as  the  water  deficits 
have  been  found  to  be  at  their  maxima  when  environmental  conditions  are  most 
severe,  that  is,  between  10  a.m.  and  3  p.m. 

"Meteorological  records  show  that  the  atmospheric  humidity  of  the  interior 
valleys  is  quite  low  during  the  growing  months,  relative  humidities  of  15  per  cent, 
being  not  uncommon.  Such  humidities  may  and  do  occur  without  marked 
increase  in  air  temperature.  In  other  words,  it  is  possible  for  extremely  dry 
weather  to  occur  without  the  characteristic  hot-norther. 

"Experiments  have  been  performed  in  the  laboratories  at  Berkeley  in  which 
this  process  of  abscission  of  leaves  on  cut  branches  has  been  induced  by  artificial 
means.  The  process  itself  has  been  studied  and  found  to  consist  in  the  gelatini- 
zation  and  dissolution  of  the  cell  walls  resulting  in  complete  separation  of  the 
cells.  .    .    . 

"  The  major  part  of  the  June  drop  occurs  early  in  the  season  and  has  to  do  with 
blossoms  and  small  fruits.  It  is  caused  by  a  stimulus  to  abscission  arising  from 
abnormal  water  relations  within  the  plant  due  to  peculiar  climatic  conditions. 

"Further  evidence  that  the  cause  as  indicated  is  substantially  correct  lies 
in  the  fact  that  in  certain  orchards  which  are  provided  with  efficient  windbreaks 
and  interplanted  with  alfalfa  and  heavily  irrigated,  the  water  deficits  in  leaves 
and  fruits  have  been  found  to  be  much  reduced.  Such  orchards  have  less  drop 
and  are  notable  for  their  comparatively  large  yields.  The  Kellogg  orchard  at 
Bakersfield  is  planted  to  alfalfa  and  is  shielded  by  a  fairly  efficient  windbreak. 
Meteorological  measurements  made  in  this  orchard  and  on  the  desert  to  windward 
show  that  the  climatic  complex  is  greatly  ameliorated.  .  .  .  The  alfalfa  tran- 
spires at  a  tremendous  rate  and  literally  bathes  the  trees  in  a  moist  atmosphere. 
The  windbreak  retards  the  movement  of  this  relatively  moist  air  away  from  the 
vicinity.  The  vaporization  of  water  from  soil  and  plants  tends  to  lower  the 
temperature  of  the  air.  As  the  soil  is  largely  shaded,  the  high  soil  temperatures 
are  reduced,  which  temperatures  operate  to  cut  down  root  absorption  at  the  time 
of  day  when  water  loss  from  the  leaves  is  greatest.    .    .    . 

"It  thus  seems  probable  that  under  the  prevalent  practice  of  clean  cultivation, 
during  the  middle  of  the  day  when  transpiration  is  greatest  the  root  absorption 
is  actually  reduced,  resulting  in  water  deficits  in  all  parts  of  the  tree. 

"  Not  only  are  clean  cultivated  orchards  subjected  to  higher  soil  temperatures, 
but  inasmuch  as  the  root  system  tends  constantly  toward  the  surface  layers,  it  is 
much  reduced  by  the  annual  spring  plowing  which  shears  off  many  of  the  fibrous 
feeders,  thus  reducing  the  root  area  just  before  blooming  and  at  the  very  time 
the  trees  are  under  the  greatest  strain. "^^ 

6 


82  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

To  what  extent  a  very  high  transpiration  may  lead  to  the  formation 
of  abscission  layers  and  the  dropping  of  fruit  in  other  varieties  and  in 
other  species  is  not  known,  but  presumably  the  phenomenon  is  not 
limited  to  the  Washington  Navel  orange.  On  the  other  hand  there  is  a 
limited  amount  of  experimental  evidence  showing  that  very  high  atmos- 
pheric humidity  tends  to  cause  the  abscission  of  partly  developed 
apples  from  the  spur.''^ 

Summary. — Evidence  from  both  tillage  and  irrigation  experiments 
shows  increased  vegetative  growth,  as  measured  by  length  of  new  shoots, 
leaf  area  and  increment  in  trunk  circumference,  with  increasing  moisture 
supply  up  to  a  certain  limit  (the  optimum  for  growth).  The  amount  of 
soil  moisture  available  during  the  short  period  of  rapid  growth  in  early 
spring  is  particularly  important.  When  the  optimum  moisture  supply 
is  exceeded  the  correlation  becomes  negative.  Second  growth  of  mid- 
summer and  the  late  summer  months  is  generally  associated  with  an 
irregular  moisture  supply.  An  increased  moisture  supply  late  in  the  sea- 
son results  in  an  increase  in  size  of  fruit  and  in  larger  yields.  Regularity 
of  bearing  is  encouraged  by  an  adequate  and  continuous  moisture  supply. 
There  is  a  limit,  however,  to  what  can  be  accomplished  in  this  direction 
through  increasing  soil  moisture.  In  certain  species,  as  the  apple,  dry 
soil  conditions  tend  to  promote  an  oblate  form  of  fruit.  There  is  no 
very  direct  relation  between  moisture  supply  and  fruit  color,  though 
good  moisture  conditions  tend  to  yield  fruits  with  brighter  colors  than 
are  obtained  from  soils  that  are  too  dry  for  best  growth  and  development 
of  tree  and  fruit.  The  higher  colors  of  fruit  from  irrigated  sections  may 
be  attributed  to  more  nearly  cloudless  skies,  in  comparison  with  those  of 
more  humid  regions.  Fruits  that  develop  where  the  soil  moisture  is 
either  deficient  or  in  excess  are  inferior  in  quality  to  those  developing 
where  soil  moisture  conditions  are  more  nearly  normal.  Disease  suscepti- 
bility is  often  modified  materially  by  the  rate  of  growth,  as  influenced 
by  soil  moisture  conditions.  The  injurious  effects  of  deficient  moisture 
supply  may  be  more  evident  the  season  following  the  drought  than  during 
its  occurrence,  taking  the  form  of  decreased  vegetative  growth  and  lowered 
yields.  The  effects  of  variations  in  atmospheric  humidity  are  hardly  less 
pronounced  than  those  in  soil  moisture  supply.  Russeting  of  fruit  is 
common  in  many  species  when  the  humidity  is  high.  Water  deficiencies 
at  the  time  of  fruit  setting  are  likely  to  result  in  an  undue  amount  of 
dropping. 


CHAPTER  VI 

PATHOLOGICAL   CONDITIONS   ASSOCIATED   WITH 
EXCESSES  OR.  DEFICIENCIES  IN  MOISTURE 

Not  only  is  water  a  limiting  factor  to  growth,  but  when  there  is  a 
deficiency  or  when  it  is  present  in  excess  well  defined  pathological  condi- 
tions may  arise.  Some  of  the  most  difficult  disorders  with  which  the 
fruit  grower  has  to  deal  are  to  be  regarded  as  drought  or  as  excess  moisture 
diseases. 

DISTURBANCES  DUE  TO  MOISTURE  EXCESSES 

Excessive  moisture  conditions  are  likely  to  be  accompanied  by  a 
disproportionate  development  of  certain  tissues  usually  parenchyma  and 
this  is  at  the  expense  of  conductive  tissue. 

The  Splitting  of  Fruit. — One  of  the  most  frequent  troubles  incident  to 
the  presence  of  too  much  water  at  certain  seasons  of  the  year  is  a  splitting 
of  the  fruit.  This  is  most  likely  to  occur  shortly  before  maturity  when 
rains  follow  a  period  of  drought  during  which  the  fruit  has  been  checked 
in  its  growth.  Apparently  the  checking  of  growth  is  accompanied  by 
changes  in  the  fruit  skin  rendering  it  less  elastic  so  that  when  growth 
processes  are  accelerated  following  a  rain  it  is  unable  to  expand  rapidly 
enough  to  make  provision  for  the  developing  tissues  within.  Heavy, 
late  irrigation  following  a  long  dry  season  has  the  same  effect.  The 
stone  fruits  are  particularly  subject  to  this  trouble  and  certain  varieties 
of  apples,  for  example  the  Stayman  Winesap,  are  likewise  susceptible. 
In  the  stone  fruits,  splitting  is  sometimes  limited  to  the  stone,  the  flesh 
and  skin  remaining  intact.  Treatment  of  this  trouble,  as  of  most  dis- 
turbed conditions  due  to  abnormal  water  relations,  should  be  preventive 
rather  than  remedial.  Cultural  practices  should  be  directed  toward 
maintaining  in  the  soil  a  moderate  amount  of  available  moisture  so  that 
growth  will  not  be  checked,  even  though  there  may  be  an  extended 
period  of  dry  weather.  Splitting  of  flesh  and  of  stones  seldom  occurs  if 
the  tissues  of  the  fruit  are  kept  growing.  It  is  suddenly  renewed  growth 
following  a  check  that  causes  the  trouble. 

In  the  fig,  splitting  may  accompany  high  atmospheric  humidity  during  the 
ripening  period  even  though  there  be  no  rain  or  no  sudden  changes  in  water 
content  of  the  soil.  However,  they  are  much  less  likely  to  split  under  such  con- 
ditions than  when  rain  accompanies  a  humid  atmosphere  so  that  the  trees  can 
take  up  an  increased  amount  of  moisture.  ^"^  Should  dry,  warm  weather  follow 
the  splitting  of  this  fruit  the  fissures  may  close  and  partially  heal  over  without 
fermentation  setting  in. 

83 


84  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Related  to  the  splitting  of  the  skin  and  fleshy  tissues  of  many  fruits 
and  the  splitting  of  the  stones  of  drupaceous  fruits  is  the  cracking  of 
carpels  and  seed  coats  frequently  found  in  apples  and  occasionally  in 
pears  and  other  pomaceous  fruits.  This  is  often  accompanied  by  the 
development  of  a  whitish  mold-like  growth  along  the  edges  of  the  cracks, 
giving  rise  to  a  condition  spoken  of  as  "tufted"  carpels  or  "tufted" 
seeds.  According  to  Sorauer^^^  this  condition  is  due  to  an  excessive 
moisture  supply  and  the  consequent  disproportionate  growth  of  certain 
cells  and  tissues.  The  "tufting"  itself  is  hardly  to  be  regarded  as  a 
diseased  condition,  for  it  is  more  or  less  common  in  certain  varieties,  but 
apparently  an  excess  of  moisture  greatly  accentuates  the  condition.  It 
in  no  way  injures  the  quality  or  value  of  the  apple,  except  as  it  provides 
a  favorable  place  for  the  work  of  certain  fungi  which  may  gain  entrance 
to  the  seed  cavity  through  a  broken  calyx  tube. 

CEdema. — Q^^dema  may  be  described  as  a  swelling  of  certain  parts 
of  a  plant  caused  by  a  great  enlargement  of  the  component  cells.  In 
extreme  cases  the  cell  walls  break  and  the  cells  collapse,  resulting  in  the 
death  of  the  affected  tissues.  This  condition  is  due  frequently  to  an 
excess  of  moisture.  It  is  favored  in  the  case  of  the  tomato  by  insufficient 
light,  too  much  soil  moisture  or  a  soil  temperature  too  high  in  comparison 
with  the  air  temperature  so  that  transpiration  cannot  take  care  of  water 
absorption.^  Sorauer^^^  states  that  in  fruit  trees  these  swellings  are 
usually  covered  by  cork  but  that  sometimes  they  break  open.  He  notes 
that  the  trouble  is  fairly  common  when  either  currants  or  gooseberries 
are  grafted  upon  the  Golden  Currant  (Ribes  aureum).  The  swellings 
develop  just  below  the  union  and  the  cion  does  not  make  a  satisfactory 
growth.  In  this  case  the  excess  of  water  is  to  be  regarded  as  a  local 
rather  than  a  general  condition. 

A  similar  disorder  in  which  the  bark  develops  at  the  expense  of  the 
wood,  has  been  described  in  the  pear,  under  the  name  "parenchyma- 
tosis."^^*  The  swellings  may  be  on  one  side  only  of  the  limb  or  trunk  or 
they  may  extend  around  it,  giving  rise  to  a  barrel  shaped  or  cylindrical 
enlargement,  which  may  be  accompanied  by  a  splitting  of  the  bark. 

Thei'e  has  been  described  a  disorder  of  the  grape  also,  more  or  less 
closely  related  to  oedema,  due  to  excessive  atmospheric  humidity.  It  is 
most  frequently  found  in  grapes  grown  under  glass.  On  the  leaves  and 
peduncles  intumescences  develop  which  are  characterized  by  great 
turgidity,  a  high  oxalic  acid  and  low  starch  content. ^^"^ 

Fasciation  and  Phyllody. — Fasciation,  or  the  production  of  a  flat 
branch  which  resembles  several  branches  grown  together  is  regarded 
generally  as  a  malformation  belonging  in  the  field  of  teratology  rather 
than  as  a  pathological  or  diseased  condition  induced  by  agencies  more  or 
less  under  control.  Sorauer,^!''  however,  places  it  among  the  distur- 
bances due  to  overfeeding  and  associated  with  excessive  water  supply. 


PATHOLOGICAL  CONDITIONS  85 

A  form  of  phyllody,  known  as  "false-blossom"  or  "Wisconsin  false- 
blossom,"  apparently  caused  by  an  excessive  water  supply  has  been 
observed  in  some  of  the  cranberry  bogs  of  the  Northern  states.  It  is 
characterized  by  more  or  less  leaf-like  calj^x  lobes  and  petals,  aborted 
or  malformed  pistils  and  stamens,  the  production  of  little  or  no  fruit  and 
an  appearance  of  the  plant  suggestive  of  witches'  broo'm.  The  trouble 
"is  usually  associated  with  extreme  wet  or  dry  conditions  of  the  bog, 
but  most  frequently  with  an  excessive  water  supply.  In  most  of  the 
localities  in  which  it  has  been  observed  the  affected  plants  were  growing 
in  a  deep,  coarse  peat  soil  having  an  excessive  water  supply  during  the 
greater  part  of  the  growing  season. "^^°  What  is  evidently  a  very  similar 
disorder,  often  caused  by  disturbed  water  relations,  has  been  described 
under  the  name  "virescence"  as  affecting  the  coffee  tree  in  Indo-China.^^ 

Chlorosis. — Chlorosis  in  plants  is  generally  associated  with  some  form 
of  malnutrition  and  some  attention  is  devoted  to  it  in  that  connection. 
However,  Taylor  and  Downing^24  found  it  accompanying  over-irrigation 
in  a  number  of  Idaho  apple  orchards.  Indeed  they  came  to  regard  it  as 
one  of  the  evidences  of  excessive  applications  of  irrigation  water.  It  is 
possible  that  the  chlorotic  condition  of  the  trees  was  induced  through 
some  influence  of  the  excess  water  supply  on  the  plant  nutrients  in  the 
soil  or  the  foods  in  the  plant,  but  directly  or  indirectly  the  surplus 
moisture  was  responsible  for  it.  A  chlorotic  condition  of  the  peach 
induced  by  over-irrigation  has  been  reported  in  Baluchistan.^"  Its  early 
symptoms  were  much  like  those  of  the  "peach  yellows"  of  the  eastern 
United  States  and  at  one  time  it  was  thought  to  be  that  disease.  It  was 
accompanied  often  by  much  gumming  and  imless  promptly  treated  the 
tree  died.  The  use  of  less  irrigation  water  and  the  employment  of  cultural 
practices  leading  to  a  better  aeration  of  the  soil  were  efficient  correc- 
tives. Chlorosis  has  been  found  in  heavily  watered  seed  beds  of  the 
western  pine  in  Nebraska  while  check  plots  showed  none.^' 

Rough  Bark  or  Scaly  Bark  Disease. — This  disease  according  to 
Sorauer^'^  results  in  a  scaling  off  of  the  bark  from  the  roots  and  to  a  less 
extent  from  the  stem.  It  has  been  described  as  affecting  the  apple, 
cherry  and  plum  when  growing  on  low,  wet  ground.  When  appearing 
on  the  roots  it  is  likely  to  cause  the  death  of  the  tree;  when  it  attacks 
the  trunk  it  is  less  serious.  Histologically  what  takes  place  is  an  excessive 
lengthening  of  some  of  the  bark  cells.  This  process  may  continue  deep 
into  the  bark  layer  and  interfere  with  normal  functions  at  the  diseased 
spot. 

Watercore. — Curiously  enough  it  is  sometimes  difficult  to  decide 
whether  a  certain  disturbance  is  due  to  drought  or  to  an  excess  of  mois- 
ture. The  temporarj^  rising  of  the  ground  water  table  may  result  in 
the  death  of  a  considerable  part  of  the  root  system.  Later,  with  lowering 
of  the  water  table  the  soil  dries  out  and  if  there  is  a  prolonged  dry  period, 


86  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

the  tree  with  its  reduced  root  system  may  suffer  for  lack  of  water  and 
drought  injury  ensue.  It  is  a  case  of  drought  injury  but  in  the  last 
analysis  excess  soil  moisture  at  another  season  is  the  real  determining 
factor.  It  is  likewise  a  paradox  that  some  forms  of  watercore  must  be 
regarded  as  due  to  drought.  Though  many  cases  are  to  be  attributed  to 
other  factors,  Sorauer^^^  describes  at  least  one  form  as  associated  with  a 
deficient  soil  moisture  supply.  In  this  form,  water  fills  the  intercellular 
spaces  and  the  affected  tissues  become  hard  and  glassy.  The  outer 
portion  of  the  fruit  is  involved  more  directly  than  the  tissues  immediately 
surrounding  the  core.  The  seeds  remain  white  and  do  not  ripen  and  the 
affected  fleshy  tissues  turn  dark  upon  exposure  to  air  more  rapidly  than 
normal  tissues.  They  have  less  dry  matter,  less  ash  and  less  acid. 
Zurich  Transparent,  Gloria  Mundi,  White  Astrachan  and  Virginia 
Summer  Rose  are  mentioned  as  varieties  particularly  susceptible  to  this 
disease. 

The  watercore  more  frequently  occurring  in  the  United  States  is 
found  in  the  core  of  the  fruit  and  in  the  region  of  the  main  vascular 
bundles,  though  it  not  infrequently  extends  to  the  surface  or  may  be 
limited  even  to  the  surface  layers.  This  form  of  watercore  is  particularly 
virulent  in  regions  of  intense  sunlight  and  abundant  soil  moisture. 
Tompkins  King,  Fall  Pippin,  Yellow  Transparent,  Early  Harvest, 
Rambo  and  Winesap  are  mentioned  as  particularly  susceptible  varieties. ^^ 

DISTURBANCES  DUE  TO  MOISTURE  DEFICIENCIES 

A  deficiency  in  the  water  supply  is  likely  to  be  accompanied  by  dis- 
turbances in  the  conductive  system  and  an  excessive  development  of 
stone  cells  and  strengthening  tissue. 

Defoliation.  Premature  Ripening  of  Wood. — Summer  drought  often 
leads  to  premature  ripening  of  the  fruit,  early  leaf  fall  and  premature 
entrance  into  the  winter  rest  period.  Frequently  the  attacks  of  certain 
fungi  hasten  these  processes  so  that  distinction  between  their  influence 
and  that  of  drought  is  difficult ;  nevertheless  there  can  be  no  doubt  that  a 
lack  of  available  moisture  has  an  important  influence  of  this  kind.  These 
effects  of  drought  are  manifest  in  various  ways  in  the  different  fruits. 
For  instance,  the  leaves  of  the  peach  and  cherry  turn  yellow  and  fall, 
those  of  the  grape  turn  yellow  or  red  at  the  edges  or  between  the  veins 
and  those  of  the  pear  do  not  become  yellow  but  appear  brown  or  burned 
in  spots  and  remain  clinging  to  the  trees.  ^^*  When  yellowing  is  due  to 
drought  injury  it  is  as  a  rule  those  parts  of  the  leaf  farthest  removed  from 
the  veins  that  yellow  first.  A  somewhat  unusual  form  of  defoliation  due 
to  a  drought  has  been  mentioned  as  a  pectin  disease."*  It  has  been 
observed  on  the  grape  and  consists  in  the  formation  of  an  abscission  layer 
between  the  leaf  blade  and  petiole,  resulting  in  the  premature  falling  of 
the  blade.     The  loss  of  leaves  from  drought  robs  the  plant  of  essential 


PATHOLOGICAL  CONDITIONS 


87 


mineral  matter,  particularly  nitrogen  and  may  interfere  in  this  way  with 
its  nutrition  as  well  as  through  reducing  the  manufacture  and  storage  of 
elaborated  organic  materials.  Table  38  shows  the  mineral  constituents 
of  Syringa  leaves  at  the  time  of  defoliation  from  drought  and  at  the  time 
of  normal  abscission.  The  yellowing  and  dropping  of  the  leaves  of 
dwarf  pear  trees  in  times  of  drought  while  those  of  standard  trees  remain 
normal  is  clear  evidence  that  the  trouble  is  due  mainly  to  a  lack  of 
moisture,  the  limited  root  system  of  the  quince  being  unable  to  supply 
the  requirements  of  the  cion  in  such  emergencies."* 

Table  38. — Mineral  Constituents  of  Syringa  Leaves  at  Different  Periods 
IN  Percentages  of  Dry  Weight 

{After  Soraiier^^*) 


When  defoliated  by 
summer  drought 

When  normally  drop- 
ping in  the  fall 

1.847 
0.522 
2.998 
1.878 
8.028 

1  370 

PhosTjhoric  ;icid 

0  373 

Potash  

Calcium  oxid 

Ash 

3.831 
2.416 
9.636 

Apparently  related  to  these  troubles  induced  by  drought  is  the  tip- 
burn  of  certain  plants  occurring  during  periods  of  very  high  transpiration. 
Even  a  few  hours  of  very  rapid  transpiration  in  intense  sunlight,  high 
temperature  and  low  atmospheric  humidity  may  lead  to  so  great  a  reduc- 
tion of  the  water  content  in  the  edges  of  the  leaves  of  the  potato  that 
recovery  of  turgidity  is  impossible. ^^  The  affected  tissues  die,  a  condition 
known  as  tip-burn. 

Another  closely  related  form  of  drought  injury  has  been  found  on  the 
grape  in  New  York.  It  is  perhaps  best  described  in  the  words  of  the 
original  report : 

"Vines  affected  with  the  trouble  first  show  a  streaked  pallidness  of  the 
leaves  in  the  intervascular  spaces.  Later  these  streaked  areas  become  yellow. 
The  discoloration  is  more  marked  near  the  margins  and  eventually  the  pallid 
areas  coalesce  and  form  a  yellowed  band  extending  around  the  margin.  As  the 
season  advances  this  band  dies  and  becomes  functionless.  Isolated  areas  of  the 
leaf  blade  deaden  and  when  these  join,  a  considerable  part  of  the  leaf  tissue  may 
become  functionless.  When  the  entire  leaf  is  affected  the  outer  margin  often 
curls  upward.  The  injury  is  cumulative  unless  favorable  conditions  are  estab- 
Ushed  in  the  succeeding  years,  i.e.,  optimum  rainfall,  etc.  As  a  result  of  the 
injury  to  the  foliage,  growth  is  materially  checked  and  the  wood  usually  fails  to 
mature  well.  The  fruit  does  not  color  nor  is  the  normal  amount  of  sugar  fixed. 
'Shelling'  may  result. 


88  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

"Considering  the  facts  at  hand  it  would  seem  that  a  lack  of  available  soil 
moisture,  at  critical  periods  in  the  vine's  growth,  or  a  lack  of  root  aeration  as  a 
result  of  the  impervious  subsoil  together  with  the  shallow  depth  of  surface  soil, 
are  the  principal  contributing  factors  to  the  affection.  With  this  soil  type  the 
sickness  is  at  its  height  in  seasons  of  drought  as  well  as  in  those  of  excessive 
rainfall.  Soils  such  as  the  yellow  silt  are  generally  deficient  in  organic  matter, 
and  hence  in  their  water-holding  capacity.  With  them  the  affection  is  worst  in 
seasons  of  drouth  and  least  in  those  of  normal  rainfall.  During  early  summer  the 
vine  makes  a  rapid  growth  of  succulent  shoots  and  leaves  which  require  large 
amounts  of  water  to  develop."^"  Newly  planted  vineyards,  where  the  vines 
do  not  yet  have  extensive  root  systems,  are  more  Ukely  to  be  affected. 

Dieback. — From  the  form  of  drought  injury  described  in  the  grape, 
it  is  but  a  step  to  more  serious  conditions  resulting  in  the  death  of 
some  of  the  twigs,  shoots  or  branches  of  the  tree.  This  may  occur  in 
trees  of  almost  any  kind,  the  symptoms  varying  somewhat  in  different 
species.  However,  there  is  no  mistaking  the  disease  when  it  is  present. 
Without  doubt  dieback  may  be  due  to  any  one  of  a  number  of  factors. 
Chief  among  these  is  an  inadequate  water  supply,  not  necessarily  at  the 
time  the  symptoms  are  first  noticed,  but  perhaps  many  months  earlier. 
Batchelor  and  Reed^^  have  described  dieback  as  it  occurs  on  the  English 
walnut.  Since  its  appearance  there  is  fairly  typical  of  its  occurrence  on 
many  other  fruit  trees  the  following  account  is  taken  from  their  report: 

"We  have  very  convincing  evidence  to  show  that  trees  which  enter  the 
dormant  period  in  the  fall  in  a  perfectly  normal  and  healthy  condition  may 
suffer  from  dieback  due  primarily  to  a  lack  of  sufficient  soil  moisture  during  the 
winter  months.  During  the  winter,  trees  give  off  moisture  through  the  Umbs 
and  twigs.  If  for  a  prolonged  period  there  is  not  enough  soil  moisture  available 
to  the  roots,  the  trees  are  unable  to  obtain  sufficient  water  to  offset  the  loss  by 
evaporation  from  the  branches.  In  that  case  young  branches,  the  thin  bark  of 
which  permits  rapid  loss  of  water  from  the  wood,  may  die  as  a  result  of  desic- 
cation. This  injury  is  first  evident  when  such  branches  fail  to  produce  new  growth 
the  following  spring.  .  .  .  Frost  injury  is  usually  confined  to  1-or  2-year  old 
wood,  but  winter  drought  may  kill  back  limbs  8  years  old. 

"Another  condition  which  is  equally  critical  and  apt  to  injure  bearing  trees, 
as  well  as  young  ones,  is  the  occurrence  of  a  fluctuating  water-table.  The  sudden 
rise  of  a  fluctuating  water-table  kills  that  portion  of  the  root  system  which  is 
located  in  the  saturated  stratum.  In  severe  cases  where  the  major  portion  of  the 
root  system  is  killed  the  twigs  and  young  hmbs  of  the  tree  later  exhibit  typical 
cases  of  'dieback.'  It  might  seem  paradoxical  that  the  top  of  the  tree  should  dry 
out  and  die  when  the  roots  stand  in  an  excessively  wet  soil,  but  there  is  nothing 
contradictory  in  the  situation  when  it  is  seen  that  the  death  of  the  major  portion 
of  the  roots  makes  it  impossible  for  the  top  to  receive  the  necessary  moisture  to 
sustain  life." 

Though  much  of  the  dieback  or  exanthema  found  in  citrus  trees  is 
due  to  disturbed  conditions  of  nutrition  there  seems  to  be  no  doubt  that 


PATHOLOGICAL  COX DIT IONS  89 

the  disease  is  generally  associated  with  abnormal  moisture  conditions. 
Trees  subject  to  poor  drainage,  underlaid  with  hardpan  or  subject 
during  the  previous  season  to  extreme  drought  or  to  an  irregular  water 
supply  are  most  subject  to  the  disease.'*^  Drought,  therefore,  must  be 
regarded  as  an  important  contributing  factor.  Other  than  the  dying 
back  of  the  limbs,  this  disease  presents  a  number  of  well  defined  symptoms 
in  citrus  trees  that  may  be  mentioned  as  further  illustrations  of  the  dis- 
turbed and  pathological  conditions  which  may  arise  from,  or  be  end 
products  of,  an  abnormal  water  supply.  Among  them  are:  the  produc- 
tion of  gum  pockets,  stained  terminal  branches,  ammoniated  fruits,  bark 
excresences,  multiple  buds,  exceptionally  deep  green  color  of  the  foliage, 
the  production  of  S-shaped  terminal  shoots  and  of  coarse  leaves  somewhat 
Hke  those  of  the  peach  in  shape. •*'■* 

Cork,  Drought  Spot  and  Related  Diseases. — Under  these  names  have 
been  described  numerous  disorders  of  fruit  trees  that  are  apparently 
related.  Indeed  differentiation  between  them  is  frequently  difficult,  if 
not  impossible.  This  is  understood  easily  because  they  are  in  fact 
closely  related  and  are  perhaps  only  different  symptoms  of  the  same 
fundamental  disturbance  in  the  physiology  of  the  plant.  The  following 
descriptions  are  from  the  reports  of  those  who  have  made  a  close  study 
of  them. 

Fruit-pit. — "  In  the  early  stages  of  fruit-pit  one  finds  numerous  sunken  areas 
from  2  to  6  millimeters  in  diameter  on  the  surface  of  the  apple.  These 
depressions  are  somewhat  hemispherical  in  shape  and  have  the  appearance  of 
bruises.  At  this  stage  the  spots  are  not  brown  and  often  show  no  difference  in 
color  from  the  surrounding  surface  of  the  apple.  .  .  .  Later  they  begin  to  take 
on  a  brown  tint,  but  at  first  this  seems  to  show  through  from  rather  deeply 
seated  tissue  and  not  to  arise  from  any  discoloration  of  the  epidermal  or  imme- 
diately underlying  cells.  Sections  of  such  spots  show  that  this  is  the  case,  and  that 
the  browning  and  shrinking  of  the  cells  occur  in  the  pulp  of  the  fruit  and  in  the 
tissue  that  is  transitional  between  it  and  the  hypodermal  parenchjona. 
Later  the  surface  cells  also  become  dark  brown.  ...  As  the  disease  advances 
spots  situated  near  each  other  often  become  confluent,  developing  into  one  large 
spot.  In  all  such  cases  examined  it  was  found  that  the  original  spots  were 
closely  connected  with  one  vascular  branch.  .  .  .  The  surface  spotting  is  often 
accompanied  by  browning  of  the  tissue  immediately  surrounding  the  vascular 
bundles.  Upon  cutting  such  an  apple  one  sees  numerous  apparently  isolated 
brown  spots.  Further  study  shows  that  these  are  not  isolated  but  are  in  reality 
continuous  strands  of  brown  tissue  surrounding  the  vascular  bundles.  The 
portion  of  the  vascular  system  that  is  most  commonly  affected  is  that  lying 
within  fifteen  miUimeters  of  the  surface  of  the  apple.  The  surface  spots  often 
occur  without  the  internal  browning  and  also  the  internal  browning  may  occur 
unaccompanied  by  any  surface  derangement. "^^ 

Cork. — Cork  is  most  commonly  observed  when  the  apple  is  anywhere  from 
half  grown  to  nearly  mature.     It  may  be  briefly  characterized  as  internal  brown- 


90  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

ing,  described  by  Brooks  in  the  preceding  paragraph,  but  without  external  pits 
and  with  the  surface  of  the  apple  thrown  into  a  series  of  elevations  and  depres- 
sions. A  large  number  of  brown  corky  areas  occur  throughout  the  flesh,  follow- 
ing closely  the  course  of  the  vascular  bundles.  In  no  case  do  these  extend 
outward  as  far  as  the  skin,  consequently  there  are  no  external  brown  pits  charac- 
teristic of  true  fruit-pit  or  stippen.  A  further  difference  from  the  usual  type 
of  fruit-pit  is  that  the  spots  are  not  more  abundant  in  the  peripheral  zone,  but 
are  scattered  throughout  the  flesh  of  the  fruit.  There  is  no  bitter  taste  connected 
with  this  disease  in  Fameuse  apples. ^^ 

"Under  the  microscope  the  internal  brown  spots  of  cork  appear  as  aggrega- 
tions of  cells  with  brown  shrunken  contents.  A  number  of  the  cells,  though  not 
all,  are  shrunken  and  collapsed.  Around  the  corky  portion  the  healthy  cortex 
cells  form  a  ladder-like  arrangement  of  smaller,  more  nearly  rectangular  cells. 
It  is  as  though  they  had  been  stimulated  to  rapid  division  in  response  to  the 
decreased  pressure  from  the  direction  of  the  diseased  area.  Outside  of  this  zone 
the  pulp  cells  are  normal  in  size  and  form.  The  close  relation  of  the  dead  spots 
to  the  vascular  system  is  very  evident  under  the  microscope. "^^ 

Surface  Drought  Spot. — "An  early  stage  of  the  disease  is  manifested  by  an 
irregular  light-brown  area  in  the  skin.  When  the  fruits  affected  are  large,  two 
or  three  centimeters  in  transverse  diameter,  the  surface  of  the  fruit  is  usually 
smooth  and  regular,  there  is  no  shrinkage  or  sinking  in,  nor  anj^  abnormality 
in  the  flesh  beneath.  .  .  .  When  the  spot  first  appears  tiny  drops  of  a  clear  or 
yellowish  gummy  exudate  may  occur  on  its  surface.  Under  the  microscope  this 
exudate  shows  as  a  clear  gum.  ...  It  is  considered  to  be  merely  an  expression 
of  cell  sap  from  the  diseased  hypodermal  cells.  .  .  .  Most  of  the  fruits 
affected  when  young  drop  from  the  tree.  Some  of  them  .  .  .  persist,  and  as 
they  grow  the  affected  areas  become  roughened  and  cracked."'^ 

Deep-seated  Drought  Spot. — "This  type  of  lesion  is  characterized  by  the 
presence  of  brown,  corky  areas  in  the  flesh  of  the  apple  and  by  a  sinking  in  of 
portions  of  the  epidermis.  On  young  fruits,  from  1  to  2  or  2J'^  centimeters  in 
transverse  diameter,  the  disease  appears  as  a  large  brownish  area  in  the  skin  of  the 
fruit,  usually  near  the  blossom  end,  which  is  irregularly  sunken  and  wrinkled, 
indicating  shrinkage  of  the  tissues  beneath.  Cross-sections  show  brown  areas 
in  the  flesh  near  the  periphery.  These  are  opposite  the  main  vascidars,  and  often 
in  the  center  of  one  of  them  there  is  a  large  cavity,  the  apex  of  which  reaches  one  of 
these  vessels.  (Occasionally,  apples  are  found  in  which  there  is  one  of  these 
corky  areas  or  cavities  opposite  each  of  the  10  main  vasculars.)  These  internal 
spots  are  often  connected  by  a  narrow  brown  streak  running  close  to  the  periphery 
of  the  apple.  Sometimes  these  streaks  do  not  connect,  but  extend  only  a  short 
distance  in  either  direction  from  the  central  spot.  The  shrinkage  of  the  skin 
over  a  considerable  area,  and  the  presence  of  these  brown  corky  spots  and  streaks 
in  the  periphery,  suggest  the  type  of  fruit-pit  described  by  McAlpine  as  'con- 
fluent bitter-pit'  or  'crinkle.'  .  .  .  Microscopically,  sections  of  the  diseased 
spots  show  that  the  trouble  is  confined  to  two  or  three  layers  of  the  hypodermal 
parenchyma,  usually  the  inner  layers,  though  sometimes  the  entire  hypodermis  is 
affected  and  a  few  dead  cells  are  also  found  in  the  flesh.  The  diseased 
cells  retain  their  normal  outline,  but  their  contents  have  become  brown  and 
amorphous. "^^ 


PATHOLOGICAL  CONDITIONS  91 

Dieback  and  Rosette. — Dieback  in  its  early  stages  appears  usually  in  the 
spring.  Some  or  all  of  the  buds  toward  the  ends  of  the  shoots  remain  dormant, 
while  lower  buds  start.  The  shoot  ends  that  do  not  vegetate  may  remain  alive 
all  season  or  they  may  dry  out  and  die  earlier.  "The  appearance  of  one  of  these 
dieback  shoots  the  following  summer  was  that  of  a  completely  dead  tip  from 
6  inches  to  1  foot  long,  often  with  a  distinct  marginal  crack  between  it  and  the 
living  part  below.  From  some  point  back  of  this  tip  a  healthy  lateral  developed 
to  renew  the  branch."'^ 

The  early  stages  of  dieback  may  be  observed  in  cross  sections  of  dieback 
twigs  of  the  current  season's  growth.  "Such  a  twig  usually  shows  entirely  dead 
tissue  near  its  tip  and  a  discoloration  in  the  cambial  area  running  back  for  a 
variable  distance.  Under  the  microscope  this  discolored  zone  shows,  if  the 
sections  are  taken  near  the  tip,  a  large  number  of  cells  with  browned  contents  in 
the  cambium,  phloem  and  pericycle.  If  sections  are  made  from  parts  of  the 
twig  a  short  distance  below,  it  will  be  seen  that  growth  has  been  made  subsequent 
to  the  injury.  The  injured  cambium  has  produced  a  quantity  of  the  so-called 
parenchyma  wood,  the  browned  cells  of  the  phloem  and  pericycle  being  pushed 
outward.  Finally,  the  parenchj^ma  zone  becomes  buried  by  a  layer  of  new 
xylem,  outside  of  which  are  found  normal  bark  and  cambium."  .  .  .  Often 
some  of  the  buds  on  the  lower  part  of  such  dieback  shoots  "developed  clusters 
of  very  small,  lanceolate  leaves  with  shortened  petioles.  In  some  cases  the  twigs 
made  a  very  short  terminal  growth,  resulting  in  a  thickened,  shortened  axis  an 
inch  or  so  long,  bearing  a  cluster  of  leaves,  some  normal  and  some  short  lanceolate, 
the  general  effect  being  that  of  a  long  bare  twig  capped  by  a  rosette  of  leaves. "^^ 

In  commenting  on  these  diseases  Mix  remarks:  "It  is  evident  that  we  have 
under  consideration,  not  two  distinct  apple  diseases,  but  at  the  most,  two  types 
of  the  same  disease:  (a)  Drouth  spot,  with  which  are  associated  abnormalities 
of  the  foliage,  called  drouth  dieback  and  drouth  rosette;  and  (6)  cork,  which 
may  occur  in  association  with  drouth  spot,  but  which  often  occurs  independently, 
and  is  then  not  associated,  except  rarely,  with  any  disease  of  the  foliage. 

"  The  writer's  observations  show  that  these  diseases  may  occur  in  both  wet  and 
dry  seasons.  There  is,  however,  a  marked  relation  of  weather  conditions  to  the 
disease.  They  tend  to  disappear  during  wet  weather  and  are  much  more  serious 
during  a  dry  period,  especially  dry  weather  occurring  early  in  the  season. 

"Since,  however,  in  a  wet  season,  and  under  conditions  where  there  seems  to 
be  no  deficiency  of  moisture,  these  diseases  may  occur  in  trees  that  have  been 
previously  diseased  year  after  year,  insufficient  soil  moisture  cannot  be  looked 
upon  as  the  sole  cause.   .    .    . 

"It  is  suggested  that  the  exact  manner  of  occurrence  of  the  injury  may  be 
by  the  leaves  robbing  the  fruit  of  water  during  a  critical  period  of  low  root  supply 
and  high  transpiration.  Rapid  wilting  of  the  fruits  can  be  brought  about  by 
excessive  transpiration  from  the  leaves.  It  has  been  seen  that  this  wilting  may 
result  in  the  death  of  certain  cells  near  the  vascular  bundles,  forming  lesions 
resembling  those  of  drouth  spot,  and  occasionally,  of  cork.  Chandler  has  pre- 
sented evidence  that  transpiration  from  the  leaves  may  bring  about  a  scarcity  of 
water  in  the  fruit  under  field  conditions.  It  is  not  impossible  that  this  is  at  least 
one  of  the  ways  in  which  the  disease  may  be  caused. 

"This  seems  more  likely  than  that  injury  is  due  to  an  excessive  transpira- 


92  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

tion  from  the  fruit  itself,  or,  as  suggested  by  McAlpine  for  'crinkle,'  to  the  failure 
of  the  vascular  network  over  large  areas.  The  striking  thing  about  these  diseases 
is  the  presence,  not  the  absence,  of  meshes  of  this  vascular  network  in  close 
proximity  to  the  dead  cell  areas. 

"In  making  the  above  suggestion  as  to  the  cause  of  cork  and  drouth  spot,  the 
writer  realizes  that  the  small  amount  of  experimental  work  done  does  not  warrant 
a  definite  conclusion.  There  is,  undoubtedly,  much  yet  to  be  learned  of  the 
real  nature  of  these  diseases. 

"Furthermore,  it  is  not  intended  to  advance  this  theory  to  explain  the  cause 
of  true  fruit-pit,  or  stippen,  which  occurs  in  a  late  stage  of  the  fruit's  growth  and 
is  said  to  develop  in  storage." 

The  findings  of  Brooks  and  Fisher,^^  who  also  made  an  extended  study 
of  drought  spot  and  cork  in  apples,  in  the  main  corroborate  the  conclusions 
of  Mix  just  quoted.  They  succeeded  in  producing  drought  spot  experi- 
mentally by  subjecting  Winesap  trees  to  a  sudden  and  severe  drought 
when  the  fruit  was  about  1  inch  in  diameter.  Furthermore,  trees  of 
other  varieties  accidentally  receiving  similar  treatment  through  mishaps 
to  the  irrigation  system  produced  fruits  exhibiting  the  same  condition. 
It  was  noted  in  the  course  of  the  investigation  that  many  trees  after  once 
producing  drought  spot  fruits  continued  to  bear  them  in  later  years, 
even  though  suitable  soil  moisture  conditions  were  provided.  This  the 
investigators  believed  to  be  due  to  the  loss  of  many  roots  when  the 
drought  occurred.  They  found  cork,  or  troubles  very  similar  to  it,  in 
many  of  the  apple  producing  sections  of  the  Pacific  Northwest  and  in 
New  York,  Virginia  and  West  Virginia.  In  summarizing  their  findings 
they  state: 

"In  nearly  every  case  where  the  disease  has  been  observed  either  in  the 
East  or  West,  its  occurrence  in  the  orchard  has  been  closely  correlated  with  certain 
peculiar  soil  conditions ;  sometimes  an  excess  of  alkali  or  an  out-cropping  of  slate, 
but  more  often  a  shallowness  or  openness  of  the  soil.  In  most  sections  cork 
has  been  most  serious  when  there  was  a  shortage  in  soil-water  supply,  either 
resulting  from  Ught  rainfall  or  a  lack  of  irrigation. 

"The  observations  reported  above  seem  to  indicate  that  cork  is  a  form  of 
drouth  injury;  yet  the  disease  appears  to  differ  from  typical  drouth  spot,  both 
in  characteristics  and  conditions  of  occurrences.  With  certain  varieties  of 
apples  drouth  spot  can  apparently  be  produced  on  any  soil  under  conditions  of 
sudden  and  extreme  drouth.  Cork  seems  to  be  the  result  of  a  less  severe  but 
more  chronic  drouth  on  trees  located  on  certain  peculiar  soils,  especially  on  soils 
that  are  lacking  in  humus  and  are  not  retentive  of  moisture.  Bhster  is  closely 
associated  with  cork  and  is  probably  produced  by  the  same  agencies. 

"It  should  be  noted  in  this  connection  that  the  harmful  effects  of  drouth  are 
not  always  in  proportion  to  the  degree  of  desiccation.  Other  factors  must  be 
considered  in  a  study  of  drouth  troubles,  and  among  these  are  the  percentage 
of  harmful  substances  in  the  soil  water  and  the  general  growth  condition  of  the 
plant."26 


PATHOLOGICAL  CONDITIONS  93 

In  the  pecan  there  is  a  related  disorder,  though  its  most  conspicuous 
symptom  is  the  appearance  of  rosetted  branches.  This  is  associated  with 
a  deficiency  of  humus  as  well  as  an  insufficient  moisture  supply  in  the  soil 
but  destruction  of  roots  through  drought  or  an  extreme  depletion  of  the 
soil  moisture  are  important  contributing  factors. ^^ 

Bitter-pit. — In  bitter-pit  "the  diseased  tissue  is  dry  and  spongy,  the  cells  are 
collapsed  but  still  full  of  starch,  and  the  cell  walls  show  no  sign  of  thickening  or 
disintegration.  .  .  .  The  pits  are  usually  associated  with  the  terminal  branches 
of  the  vascular  bundles,  and  the  surface  spotting  is  often  accompanied  by  a 
browning  of  the  vascular  tissue  deeper  in  the  fruit,  giving  the  appearance  of  nu- 
merous brown  spots  in  the  flesh  when  the  apple  is  cut.    .    .    . 

"The  results  of  the  various  experiments  have  been  uniformly  consistent  in 
showing  that  heavy  irrigation  favors  the  development  of  bitter-pit.  Heavy 
irrigation  throughout  the  season  has  given  less  of  the  disease  than  medium  irri- 
gation followed  by  heavy,  and  light  irrigation  throughout  the  season  has  resulted 
in  more  bitter-pit  than  heavy  irrigation  followed  bj^  light.  Heav"^^  irrigation  the 
first  half  of  the  season  caused  the  trees  to  develop  a  more  luxuriant  foliage  and 
probably  produced  a  lower  concentration  of  cell  sap  in  the  apples,  both  of  which 
facts  would  tend  to  make  the  fruit  less  susceptible  to  the  forcing  effects  of  late 
irrigation.  The  amount  of  irrigation  in  August  and  September  has  apparently 
largely  determined  the  amount  of  disease. 

"Sudden  changes  in  the  amount  of  soil  water  do  not  appear  to  have  had  any 
effect  upon  the  amount  of  disease.  No  evidence  has  been  found  that  bitter-pit 
is  brought  about  by  a  rupture  or  bursting  of  the  cells. 

"Large  apples  have  been  more  susceptible  to  bitter-pit  than  small  ones,  but 
the  increase  in  the  disease  from  heavy  irrigation  has  been  almost  as  great  on  the 
small  and  medium  sized  fruits  as  on  the  large.  .  .  .  Apparently  apples  are  not 
susceptible  to  bitter-pit  merely  because  they  are  large,  but  rather  because  of 
conditions  that  may  sometimes  accompany  an  increased  growth. 

"The  results  as  a  whole  point  to  the  harmful  effects  of  heav>^  late  irrigation 
regardless  of  the  size  of  the  fruit.  In  looking  for  the  final  cause  of  the  disease  not 
only  the  direct  growth-forcing  effects  of  the  water  should  be  considered  but  also 
the  effects  of  the  excess  water  upon  the  soil  flora  and  soil  solutes."" 

Jonathan-spot. — "  'Jonathan-spot'  is  the  term  applied  to  superficial  black  or 
brown  spots  that  are  especially  common  on  Jonathan  apples.  ...  In  the  early 
stages  of  the  disease  only  the  surface  color-bearing  cells  are  involved  and  the 
spots  are  seldom  more  than  2  mm.  in  diameter,  but  later  the  spots  may  enlarge 
to  a  diameter  of  3  to  5  mm.,  become  slightly  sunken  and  spread  down  into  the 
tissue  of  the  apple  to  a  considerable  depth.  .  .  .  The  results  of  both  years 
gave  some  evidence  that  heavy  irigation  was  more  favorable  to  the  disease  than 
light  irrigation,  but  there  was  nothing  to  indicate  that  the  amount  of  soil  moisture 
was  an  important  factor  in  determining  the  amount  of  Jonathan  spot."^^ 

To  what  extent  these,  or  similar  diseases  are  to  be  found  in  other 
fruits  is  unknown.  There  is  reason  to  beheve,  however,  that  just  as  some 
of  these  diseases  of  the  apple  have  been  dismissed  as  winter  injury  or  as 


94  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

some  other  rather  obscure  disorder,  so  some  of  the  serious  troubles  of  these 
other  fruits  may  prove  eventually  to  be  due  directly  or  indirectly  to 
drought.  Rosette  and  little-leaf  are  certainly  not  unknown  in  the  cherry, 
apricot,  plum  and  pear  though  little  attention  has  been  devoted  to  them. 

Barss'"  records  "cork"  as  of  frequent  occurrence  in  pears  in  Oregon  and  a 
"drought  spot  "or  "gum-spot  "as  not  uncommon  in  prunes.  Both  are  attributed 
to  disturbed  water  relations.  In  speaking  of  the  gum-spot  of  prunes  he  says: 
"It  comes  on  just  about  in  midseason  and  appears  first  as  watery-looking  spots 
on  the  fruit.  These  usually  swell  and  burst  open  by  a  crescent-shaped  sht,  from 
which  there  is  an  exudation  of  transparent  gum  that  hardens  on  the  surface.  In 
the  flesh  of  such  prunes  small  brown  flecks  always  appear,  beneath  the  gum- 
spot.  These  usually  consist  of  a  few  dead  pulp  cells  situated  in  the  region  of  the 
outer  network  of  veins.  Such  injury  is  often  slight  and  the  prunes  mature  with 
very  little  evidence  of  the  trouble.  More  severe  injury,  however,  may  result  in 
the  death  of  larger  areas  of  the  pulp.  The  resulting  collapse  of  the  tissues  and 
cessation  of  growth  produces  an  irregular  or  corrugated  surf  ace.  Such  affected 
prunes  usually  color  up  prematurely  and  drop  off. 

"In  some  years,  as  the  prunes  approach  maturity  great  losses  to  growers 
result  from  an  internal  breaking  down  of  the  flesh,  with  brown  discoloration  and 
disagreeable  odor,  which  has  sometimes  been  erroneously  mistaken  for  brown 
rot.  This  internal  browning  usually  starts  immediately  around  the  pit,  but  often 
extends  outward  until  in  some  cases  it  reaches  the  skin  and  involves  the  whole 
flesh.  The  trouble  is  .  .  .  presumably  due  to  disturbed  water  balance  in 
the  tree  and  perhaps  is  similar  in  origin  to  'punk'  in  the  apple." 

The  assumption  should  not  be  made,  however,  that  all  these  diseases 
described  and  discussed  here  under  the  names  of  cork,  fruit-pit,  bitter- 
pit,  Jonathan-spot,  dieback,  rosette,  etc.  are  always  due  exclusively  to 
disturbed  water  relations.  Though  without  doubt  they  often  are  caused 
directly  or  indirectly  by  excessive  moisture  or  by  drought,  there  are 
other  contributing  factors  and  in  some  instances  their  occurrence 
may  be  due  to  these  other  factors  alone.  For  instance,  White  ^^^  ^nd 
Ewert*'''  ^^  present  evidence  that  in  Australia  much  of  the  bitter-pit  in  the 
apple  is  due  to  localized  poisoning  caused  by  the  presence  of  minute 
quantities  of  certain  mineral  toxins  absorbed  either  from  the  soil  or  from 
the  coating  of  certain  spray  materials  on  the  fruit  itself. 

Black-end. — Under  the  name  black-end  has  been  described  a  physiological 
disease  of  pears  in  which  the  skin  around  the  apical  end  of  the  fruit  turns  black 
while  the  flesh  immediately  underneath  becomes  hard  and  dry  and  may  crack. i° 
Such  fruits  are  likely  to  be  rounded  at  the  apical  end  instead  of  depressed  in  the 
usual  manner.  The  blackened  area  often  blends  gradually  into  healthy  tissue. 
This  disease  is  found  most  frequently  in  the  hotter  and  drier  portions  of  Oregon , 
and  "all  the  circumstantial  evidence  points  to  the  probabiHty  that  excessive 
evaporation  in  hot  weather  or  insufficient  soil  moisture  are  responsible  for  its 
development,  since  it  appears  usually  on  soils  either  unfavorable  for  root 
growth  or  unretentive  of  moisture  or  both." 


PATHOLOGICAL  CONDITIONS  95 

Silver  Leaf. — Sorauer^^''  describes  one  type  of  silver  leaf  occurring 
on  apricots,  plums,  cherries  and  apples.  The  immediate  cause  of  the 
silvery  or  milky  appearance  of  the  leaves  is  the  partial  separation  of  the 
epidermal  cells  from  one  another  and  from  the  palisade  cells,  the  inter- 
cellular spaces  becoming  greatly  enlarged.  The  older  leaves  are  more 
subject  than  the  younger.  This  disease  is  usually  associated  with  some 
gummosis  of  the  limbs  and  in  aggravated  cases  the  affected  branches  die. 
Aderhold  suggests  that  the  failure  of  the  middle  lamella  to  cement 
adjoining  cells  is  due  to  a  lack  of  calcium,  which  permits  the  pectin  to 
become  soluble.  As  the  disease  generally  occurs  locally  in  the  plant, 
the  lack  of  calcium  is  not  the  result  of  a  deficiency  in  the  soil  but  is  due 
to  a  local  disturbance  in  the  conducting  system. 

Some  other  forms  of  silver  leaf  occasionally  appearing  in  the  orchard 
and  affecting  entire  trees  or  entire  orchards  may  be  due  to  quite  different 
causes. 

Lithiasis. — Drought  at  or  shortly  before  the  riaaturing  season  of  pears 
has  been  noted  often  to  cause  increased  grittiness  of  the  flesh,  the  stony 
aggregations  around  the  core  becoming  larger.  Sorauer^^^  describes  an 
aggravated  form  of  this  trouble  under  the  name  lithiasis.  In  this  drought 
disease  sclerotic  tissue  develops  near  the  surface  of  the  fruit,  particularly 
on  the  sunny  side.  Ordinarily  it  is  found  only  in  cases  of  extreme 
drought. 

Summary. — Either  an  excess  or  a  deficiency  in  soil  moisture  is  likely 
to  be  accompanied  by  a  disturbed  condition  within  the  plant  and  often 
by  the  appearance  of  some  pathological  symptom.  Among  those  brought 
on  by  excesses  in  the  moisture  supply  are  fruit  splitting,  fasciation,  phyl- 
lody,  oedema,  chlorosis,  scaly  bark  and  water  core.  High  atmospheric 
humidity  is  an  important  contributing  factor  in  oedema;  fruit  splitting 
is  due  to  an  irregular  soil  moisture  supply  as  much  as  to  an  excess. 
Measures  against  all  of  these  troubles  should  be  preventive  rather  than 
remedial.  They  include  provision  for  adequate  drainage  and  caution 
in  the  use  of  irrigation  water.  Premature  defoliation  and  the  attend- 
ant ripening  of  the  wood  is  one  of  the  more  serious  results  of  a  moisture 
deficiency.  It  is  likely  to  be  followed  by  decreased  vegetative  growth, 
lessened  yields  and  in  extreme  cases,  dieback.  The  earlier  entrance 
into  the  rest  period  and  the  poorer  maturity  of  the  wood  both  tend 
toward  susceptibility  to  winter  injury.  Dieback,  rosette  and  little- 
leaf  are  closely  related  disorders  of  the  tree  due  in  many  cases  to  summer 
drought.  Often  associated  with  these  tree  diseases,  but  sometimes  more 
or  less  independent  of  them,  are  a  number  of  closely  related  diseases  of  the 
fruit  itself  that  have  been  described  under  the  names:  fruit-pit,  cork, 
drought  spot,  bitter-pit,  Baldwin-spot,  Jonathan-spot  and  black-end. 
It  is  probable  that  some  of  these  terms  as  commonly  used  refer  to  one  and 
the  same  trouble,  or  at  least  they  overlap.     This  group  of  disorders, 


96  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

though  directly  due  to  (h'ought,  frequently  may  be  a  result  of  too  much 
moisture,  or  a  water  table  too  high  at  some  other  season,  resulting  in  a 
restricted  root  system.  Here  again,  protection  lies  more  in  preventive 
than  in  remedial  treatments. 

Suggested  Collateral  Readings 

1.  Schimper,   A.  F.   W.     Plant  Geography.     (English  Translation)   Oxford,    1903. 

(Particularly  pp.  159-173,  81-85.) 

2.  Bowman,  I.     Forest  Physiography.     New  York,   1914.     (Chapter  3  on  Water 

Supply  of  Soils;  Relation  to  Plant  Growth  and  Distribution,  pp.  41-54.) 

3.  Weaver,  J.  E.     The  Ecological  Relations  of  Roots.     Pub.  286  Carnegie  Inst,  of 

Washington.     1919.     (Particularly  pp.  27-28,  100-108,  121-127.) 

4.  Hilgard,  E.  W.,  and  Loughridge,  R.  H.     Endurance  of  Drought  in  Soils  of  the 

Arid  Region.     Rept.  Cal.  Agr.  Exp.  Sta.  for  1897-8.     Pp.  40-64. 

5.  Loughridge,  R.  H.     Moisture  in  California  Soils  During  the  Dry  Season  of  1898. 

Rept.  Cal.  Agr.  Exp.  Sta.  for  1897-8.     Pp.  6.5-96. 

6.  Mason,   S.   C.     Drought  Resistance  of  the  Olive  in  the  Southwestern  States. 

U.  S.  D.  A.,  Bur.  PI.  Ind.  Bui.  192,  pp.  9-33.     1911. 

7.  Huntington,  E.,  and  others.     The  Climatic  Factor  as  Illustrated  in  Arid  America. 

Pub.  Carnegie  Inst,  of  Washington,  pp.  101-174.     1914. 

8.  Whitten,  J.  C.     An  Investigation  in  Transplanting.     Mo.  Agr.  Exp.  Sta.  Res. 

Bui.  33.     1919. 

9.  Bates,  C.  G.     Windbreaks;  Their  Influence  and  Use.     U.  S.  D.  A.,  Forest  Service 

Bui.  86.     1911. 

10.  Gourley,   J.   H.     Some   Observations  on   the   Growth   of   Apple   Trees.     N.    H. 

Agr.Exp.  Sta.  Tech.  Bui.  12.     1917. 

11.  Green,  W.  J.,  and  Ballou,  F.  H.     Orchard  Culture.     Ohio  Agr.  Exp.  Sta.  Bui.  171. 

1906. 

12.  Hedrick,  U.  P.     A  Comparison  of  Tillage  and  Sod  Mulch  in  an  Apple  Orchard. 

N.  Y.  Agr.  Exp.  Sta.  Bui.  314.     1909. 

13.  Hedrick,  U.  P.     Tillage  and  Sod  Mulch  in  the  Hitchings  Orchard.     N.  Y.  Agr. 

Exp.  Sta.  Bui.  375.     1914. 

14.  Mix,  A.  J.     Cork,  Drouth  Spot  and  Related  Diseases  of  the  Apple.     N.  Y.  Agr. 

Exp.  Sta.  Bui.  426.     1916. 

15.  Gladwin,  F.  E.     A  Non-parasitic  Malady  of  the  Vine.     N.  Y.  Agr.  Exp.  Sta. 

Bui.  499.     1918. 

16.  Briggs,  L.  J.,  and  Shantz,  H.  L.     The  Water  Requirement  of  Plants.     A  Review 

of  Literature.     U.  S.  D.  A.,  Bur.  PI.  Ind.  Bui.  285.     1913. 

Literature  Cited 

1.  Agr.  Jour.  India.     13:  150.     1918. 

2.  Allen,  R.  W.     Ore.  Agr.  Exp.  Sta.  Rept.  of  the  Hood  River  Branch  Exp.  Sta. 

Pp.  20-24.     1914-15. 

3.  Andre,  G.     Chimie  agricole.     1:485.     Paris,  1914. 

4.  Atkins,   W.   R.   G.     Some  Recent  Researches  in   Plant  Physiology.     P.   201. 

London,  1916. 

5.  Atkinson,  G.  F.     Cornell  Univ.  Agr.  Exp.  Sta.  Bui.  53.     1893. 

6.  Babcock,  S.  M.     Wise.  Agr.  Exp.  Sta.  Research  Bui.  22.     1912. 

7.  Bailey,  L.  H.     Mich.  Agr.  Exp.  Sta.  Bui.  31.     1887. 

8.  Ballantyne,  A.  B.     Utah  Agr.  Exp.  Sta.  Bui.  143.     1916. 


WATER  RELATIONS  97 

9.  Barss,  A.  F.     Bienn.  Crop  Pest  and  Hurt.  Rept.     Ore.  Agr.  Exp.  Sta.      1 :  38-49. 
1913-14. 

10.  Bars.s,    H.    P.     Bienn.    Crop    Pest    and    Hort.    Rept.     Ore.    Agr.    Exp.    Sta. 

3:  159-166.     1921. 

11.  Batchelor,  L.  D.     Utah  Agr.  Exp.  Sta.  Bui.  142.     1916. 

12.  Batchelor,  L.  D.,  and  Reed,  H.  S.     Cal.  Agr.  Exp.  Sta.  Circ.  216.     1919. 

13.  Bates,  C.  G.     U.  S.  D.  A.,  Forest  Service  Bui.  86.     1911. 

14.  Bedford,  H.  A.  R.,  and  Pickering,  S.  U.     Science  and  Fruit  Growing.     P.  283. 

London,  1919. 

15.  Bergman,  H.  F.     Ann.  Bot.     34:  13-33.     1920. 

16.  Boussingault,  J.     Agronomic.     6:  349.     1878. 

17.  Bouyoucos,  G.  J.     Mich.  Agr.  Exp.  Sta.  Tech.  Bui.  36.     1917. 

18.  Bowman,  I.     Forest  Physiography.     P.  42.     New  York,  1914. 

19.  Ibid.     P.  66. 

20.  Briggs,  L.  J.,  and  Shantz,  H.  L.     U.  S.  D.  A.,  Bur.  PL  Ind.  Bui.  230.     1912. 

21.  Briggs,  L.  J.,  and  Shantz,  H.  L.     U.  S.  D.  A.,  Bur.  PL  Ind.  Bui.  285.     1913. 

22.  Briggs,     L.    J.,    and  Shantz,   H.  L.     Proc.   Pan-Amer.   Sci.   Cong.     3:95-107. 

1915-16.     (Reviewed  in  Exp.  Sta.  Rec.     41:632.     1919.) 

23.  Briggs.  L.  J.,  Jensen,  C.  A.,  and  McLane,  J.  W.     U.  S.  D.  A.  Bui.  499.     1917. 

24.  Brooks,  C.     Torrey  Bui.     35:  423-456.     1908. 

25.  Brooks,  C,  and  Fisher,  D.  F.     Jour.  Agr.  Research.     13:  109-137.     1918. 

26.  Brooks,  C,  Cooley,  J.  S.,  and  Fisher,  D.  F.     U.  S.  D.  A.,  Farmers'  Bui.  1160. 

1920. 

27.  Brown,  G.     Jour.  Ecology.     3:  30-31.     1915. 

28.  Burgerstein,  A.     Oester.  bot.  Zeitsch.     25:  6.     1875. 

29.  Burgerstein,  A.     Sitzungsb.  d.  Wien.  Akad.     73:  abt.  1  Riehe  2;  78.     1876. 

30.  Buttenshaw,  W.  R.     Mo.  Weather  Rev.     32:  470.     1904. 

31.  Caldwell,  J.  S.     Physiological  Researches.     1.     1913. 

32.  Cannon,  W.  A.     Carnegie  Inst.  Wash.  Yearbook.     17:  83-85.     1919. 

33.  Card,  F.  W.     Neb.  Agr.  Exp.  Sta.  Bui.  48.     1897. 

34.  Chandler,  W.  H.     Mo.  Agr.  Exp.  Sta.  Research  Bui.  14.     1914. 

35.  Coit,  J.  E.,  and  Hodgson,  R.  W.     Cal.  Agr.  Exp.  Sta.  Bui.  290.     1918. 

36.  Corbett,  L.  C.     S.  D.  Agr.  Exp.  Sta.  Bui.  44.     1895. 

37.  Coville,  F.  V.     U.  S.  D.  A.,  Bur.  PL  Ind.  Bui.  193.     1910. 

38.  Craig,  J.     Cornell  Univ.  Agr.  Exp.  Sta.  Bui.  198.     1902. 

39.  Cramer,  P.  J.  S.     Phillipine  Agr.  Rev.     3:94-100.     1910. 

40.  Darwin,  F.     Proc.  Roy.  Soc.     B87:  281-299.     1914. 

41.  Delwiche,  E.  J.,  and  Moore,  J.  G.     Wis.  Agr.  Exp.  Sta.  Rept.     P.  382.     1907. 

42.  Dixon,  H.  H.     Transpiration  and  the  Ascent  of  Sap  in  Plants.     London,  1914. 

43.  Duggar,  B.  M.     Plant  Physiology.     P.  87.     New  York,  1912. 

44.  Eberdt,  O.     Die  Transpiration  der  Pflanze  and  ihre  Abhangigkeit  von  aiisseren 

Bedingungen.     P.  88.     Marburg,  1889. 

45.  Emerson,  R.  A.     Neb.  Agr.  Exp.  Sta.  Bui.  79.     1903. 

46.  Ibid.     Bui.  92.     1906. 

47.  Ewert,  A.  J.     Proc.  Roy.  Soc.  Victoria.     24  (N.  S.):  367-419.     1911. 

48.  Ibid.     26  (N.  S.):  2-44,  226-242.     1914. 

49.  Floyd,  B.  F.     Fla.  Agr.  Exp.  Sta.  Bui.  140.     1917. 

50.  Gladwin,  F.  E.     N.  Y.  Agr.  Exp.  Sta.  Bui.  499.     1918. 

51.  Gloyer,  W.  O.     N.  Y.  Agr.  Exp.  Sta.  Bui.  485.     1921. 

52.  Gourley,  J.  H.,  and  Shunk,  V.  D.     N.  H.  Agr.  Exp.  Sta.  Tech.  Bui.  11.     1916. 

53.  Gourley,  J.  H.     N.  H.  Agr.  Exp.  Sta.  Tech.  Bui.  12.     1917. 

54.  Green,  W.  J.,  and  Ballou,  F.  H.     Ohio  Agr.  Exp.  Sta.  Bui.  171.     1906. 


98  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

55.  Haberlandt,  G.     Physiological  Plant  Anatomy.     English  translation.     P.  219. 

London,  1914. 

56.  Hartig,  T.     Allg.  Forst  u.  Jagdzeit.  N.  F.  54.     1878. 

57.  Hartig,  T.     Bot.  Centralblatt  36:  388-391.     1888 

58.  Hasselbring,  H.     Bot.  Gaz.     57:  72-73.     1914. 

59.  Hedrick,  U.  P.     N.  Y.  Agr.  Exp.  Sta.  Bui.  314.     1909. 

60.  Hedrick,  U.  P.     N.  Y.  Agr.  Exp.  Sta.  Bui.  375.     1914. 

61.  Heinicke,  A.  J.     Cornell  Univ.  Agr.  Exp.  Sta.  Bui.  393.     1917. 

62.  Hellriegel,  F.  H.     Beitrage   zu   den   Natur   wissenschaftlichen   Grundlagen  des 
Ackerbaus.     Pp.      662-664     Braunschweig,  1883. 

63.  Hilgard,  E.  W.     Soils,  6th  Edition.     Pp.  168-171,  245.     New  York,  1914. 

64.  Ibid.     P.  200. 

65.  Ibid.     P.  263. 

66.  Hilgard,  E.  W.,  and  Loughridge,  R.  H.     Cal.  Agr.  Exp.  Sta.  Rept.     Pp.  41,  56. 

1897-8. 

67.  Hooker,  H.  D.,  Jr.     Ann.  of  Bot.     29:  265-283.     1915. 

68.  Hooker,  H.  D.,  Jr.     Mo.  Agr.  Exp.  Sta.  Research  Bui.  40.     1920. 

69.  Hooker,  H.  D.,  Jr.     Proc.  Am.  Soc.  Hort.  Sci.     17:  204-207.     1920. 

70.  Howard,  A.     Rept.  Agr.  Research  Inst.  Pusa.     P.  43.     1913-14. 

71.  Howard,  A.,  and  Howard,  G.  L.  C.     Agr.  Research  Inst.  Pusa.  Buls.  52  and  61. 

1915-16.     (Abs.  in  Plant  World.     20:  260-262.     1917.) 

72.  Huntington,   E.     The  Climatic  Factor  as  Illustrated  in  Arid  America.     Pp. 

101-174.     Carnegie  Inst.  Washington,  1914. 

73.  Jones,  F.  R.     A  Study  of  the  Development  and  Extent  of  the  Roots  of  Apple 

Trees.     1912.     Unpublished  Thesis  on  file  in  the  Library  of  the  University  of 
Maine. 

74.  Jones,  J.  S.,  and  Colver,  C.  W.     Ida.  Agr.  Exp.  Sta.  Bui.  75.     1912. 

75.  Kearney,  T.  H.     U.  S.  D.  A.,  Bur.  PI.  Ind.  Bui.  125.     1908. 

76.  Kelley,  W.  P.,  and  Thomas,  E.  E.     Cal.  Agr.  Exp.  Sta.  Bui.  318.     1920. 

77.  King,   F.  H.     Physics  of  Agriculture.     2d  Edition.     P.   131.     Madison,  Wis. 

1901. 

78.  Ibid.     P.  189. 

79.  King,  F.  H.     U.  S.  D.  A.,  Bur.  Soils  Bui.  26.     1905. 

80.  Kohl,  F.  G.     Die  Transpiration  der  Pfanzen.     Brunswick,  1886. 

81.  Korstian,    C.   F.,    Hartley,    C,    Watts,   L.   F.,    and   Hahn,   G.  G.     Jour.  Agr. 
Research.     21:  153-169.     1921. 

82.  Kosaroff,  P.     Einfluss  verschiedenen  ausseren  Faktoren  auf  die  Wasseraufnahme 

der  Pflanzen.     Dissertation.     Leipzig,  1897. 

83.  Leather,  J.  W.     Cited  by  J.  W.  Patterson.     Jour.  Agr.  Victoria.     10:353.     1912. 

84.  Lepeschkin,  W.  W.     Beih.  Botan.  Centralbl.     19:  409-452.     1906. 

85.  Lewis,  C.  I.,  Kraus,  E.  J.,  and  Rees,  R.  W.     Ore.  Agr.  Exp.  Sta.  Bui.  113.     1912. 

86.  Loughridge,  R.  H.     Cal.  Agr.  Exp.  Sta.  Rept.     Pp.  61,  64,  66.     1897-98. 

87.  Ibid.     Pp.  82,  94,  95,  96. 

88.  Lutman,  B.  F.     Vt.  Agr.  Exp.  Sta.  Bui.  214.     1919. 

89.  Lyon,   T.  L.,   and  Fippin,   E.  O.     The  Principles  of  Soil   Management.     4th 

Edition.     New  York,  1911. 

90.  Ibid.     P.  192. 

91.  Mason,  S.  C.     U.  S.  D.  A.,  Bur.  PI.  Ind.  Bui.  192.     1911. 

92.  Mason,  S.  C.     U.  S.  D.  A  Bui.  271.     1915. 

93.  McCool,  M.  M.,  and  Millar,  C.  E.     Soil  Sci.     9:  217-233.     1920. 

94.  McCue,  C.  A.     Del.  Agr.  Exp.  Sta.  Bui.  120.     1918. 

95.  McLaughlin,  W.  W.     U.  S.  D.  A.  Bui.  835.     1920. 


WATER  RELATIONS  99 

96.  McMurran,  S.  M.     U.  S.  D.  A.  Bui.  756.     1919. 

97.  Mix,  A.  J.     N.  Y.  Agr.  Exp.  Sta.  Bui.  426.     1916. 

98.  Morse,  W.  J.     Me.  Agr.  Exp.  Sta.  Bui.  271.     1918. 

99.  Nisbit,  J.     Studies  in  Forestry.     P.  77.     Oxford,  1894. 

100.  Palladin,  W.     Ber.  Deutsch.  Bot.  Ges.     8:  364-371.     1890. 

101.  Palmer,  A.  H.     U.  S.  D.  A.,  Mo.  Weather  Rev.     48:  151-154.     1920. 

102.  Pearson,  G.  A.     Jour.  Forestry.     16:  677-683.     1918. 

103.  Pulling,  H.  E.     Plant  World.     21:223-233.     1918. 

104.  Rixford,  G.  P.     U.  S.  D.  A.  Bui.  732.     1918. 

105.  Rosa,  J.  T.  Jr.     Proc.  Am.  See.  Hort.  Sci.     17:  207-210.     1920. 

106.  Rotmistrov,   V.   G.     Nature  of   Drought  According  to   the  Evidence  of   the 

Odessa  Experiment  Station,  Russia.     Eng.  Edition.     P.  20.     Odessa,  1913. 

107.  Russell,  T.     Cited  by  S.  B.  Green.     Minn.  Agr.  Exp.  Sta.  Bui.  32.     1893. 

108.  Schnee,  F.     tJber  den  Lebenszustand  allseitig  verkorkter  Zellen.     Dissertation. 

Leipzig,  1907. 

109.  Schwartz,  F.     Unters.  a.  d.  Bot.  Inst,  zu  Tubingen.     1:140.     1883. 

110.  Shear,  C.  L.     U.  S.  D.  A.,  Farmers'  Bui.  1081.     1920. 

111.  Smith,  J.  W.     U.  S.  D.  A.,  Mo.  Weather  Rev.     48:  446.     1920. 

112.  Sorauer,  P.     Pflanzenkrankeiten.     3te  Auflage.     1:169-170.     Berlin,  1909. 

113.  Ibid.     P.  210. 

114.  Ibid.     P.  275,  284-285. 

115.  Ibid.     P.  286. 

116.  Ibid.     P.  324. 

117.  Ibid.     P.  332. 

118.  Ibid.     P.  335. 

119.  Ibid.     P.  422. 

120.  Ibid.     P.  435. 

121.  Spoehr,  H.  A.     Carnegie  Inst.  Wash.  Publ.  287.     1919 

122.  Stewart,  J.  P.     Pa.  Agr.  Exp.  Sta.  Bui.  134.     1915. 

123.  Stewart,  J.  P.     Pa.  Agr.  Exp.  Sta.  Bui.  141.     1916. 

124.  Taylor,  E.  P.,  and  Downing,  G.  J.     Ida.  Agr.  Exp.  Sta.  Bui.  99.     1917. 

125.  Thompson,  R.  C.     Ark.  Agr.  Exp.  Sta.  Bui.  123.     1916. 

126.  Tucker,  M.,  and  von  Seelhorst,  C.     Journ.  f.  Landw.     46:  52-63.     1898. 

127.  Tufts,  W.  P.     Letter  to  one  of  the  authors,  dated  March  21,  1921. 

128.  U.  S.  D.  A.,  Div.  Agr.  Soils  Buls.  1,  2  and  3.     1895. 

129.  Van  Slyke,  L.  L.,  Taylor,  O.  M.,  and  Andrews,  W.  H.     Geneva  Agr.  Exp.  Sta. 

Bui.  265.     1905. 

130.  Von  Seelhorst,  C.     Journ.  f.  Landw.     58:  83-88.     1910. 

131.  Weaver,  J.  E.     Cam.  Inst.  Wash.  Publ.  286.     1919. 

132.  White,  J.     Proc.  Roy.  Soc.  Victoria.     24  (N.  S.):  2-16.     1911. 

133.  Whitehouse,  W.  E.     Ore.  Agr.  Exp.  Sta.  Bui.  134.     1916. 

134.  Whitten,  J.  C.     Mo.  Agr.  Exp.  Sta.  Bui.  49.     1900. 

135.  Whitten,  J.  C.     Mo.  Agr.  Exp.  Sta.  Research  Bui.  33.     1919. 

136.  Widtsoe,  J.  A.     Dry  Farming.     P.  185.     New  York,  1911. 

137.  Wiggins,  P.  G.     Am.  Jour.  Bot.     8:  30-40.     1921. 

138.  Woodbury,  C.  G.,  Noyes,  H.  A.,  and  Oskamp,  J.     Purdue  Univ.    Agr.    Exp. 

Sta.  Bui.  205.     1917. 

139.  Zon,  R.     Proc.  Soc.  Amer.  Foresters.     2:  79.     1907. 


SECTION  II 
NUTRITION 

Nutrient  supply  is  generally  considered  the  most  important  of  the 
factors  limiting  growth  and  productiveness.  Certainly  it  ranks  second 
to  no  other  in  determining  the  success  or  failure  of  the  orchard  enter- 
prise within  those  sections  or  areas  where  climatic  conditions  make 
possible  a  fruit  industry  and  where  economic  conditions  make  practicable 
its  development.  Though  there  are  many  single  cases  in  which  the 
water  supply,  the  prevalence  of  pests  or  some  other  factor  assumes 
paramount  importance,  the  most  common  limiting  influence  is  associated 
with  nutritive  conditions.  Much  of  the  effort  of  the  careful  grower  is 
directed  toward  relieving  his  plants  from  unnecessary  competition  and 
struggle  for  a  nutrient  supply. 

Few  general  questions  pertaining  to  fruit  growing  have  been  less 
thoroughly  understood  than  soil  productivity  as  it  relates  to  tree  growth. 
This  condition  has  existed  mainly  because  of  the  assumption  by  analogy 
that  the  requirements  of  trees,  vines  or  other  fruit  producing  plants  are 
practically  identical  with  those  of  annual  crops  and  because  until  very 
recently  experimental  evidence  upon  which  to  base  reliable  interpre- 
tations and  Conclusions  has  been  lacking.  Trees,  shrubs  and  vines  have 
life  histories,  even  seasonal  life  histories,  quite  different  from  those  of 
annuals.  It  is  to  be  expected,  therefore,  that  they  possess  quite  different 
nutrient  requirements  or  at  least,  quite  different  feeding  habits.  These 
nutrient  requirements  and  feeding  habits  must  be  studied  thoroughly 
before  there  can  be  a  proper  appreciation  of  the  orchard  soil  productivity 
problem. 


100 


CHAPTER  VII 

PLANT  NUTRIENTS  AND  THEIR  ABSORPTION 

Plants  require  for  their  nutriment  water,  carbon  dioxide,  oxygen, 
nitrates  (or  other  nitrogen  carrying  compounds),  sulphates,  phosphates, 
salts  of  iron,  magnesium,  potassium  and  calcium.  Though  chemical 
analysis  of  plant  tissue  shows  that  almost  every  clement  may  be  found 
in  one  plant  or  another,  carbon,  hydrogen,  oxygen,  nitrogen,  phosphorus, 
sulphur,  potassium,  magnesium,  iron,  calcium,  chlorine,  silicon,  sodium, 
aluminum  and  manganese  are  found  in  practically  all  plants.  The 
first  ten  of  these  are  necessaiy  for  all  the  higher  plants.  Water,  nitrogen 
and  all  the  mineral  elements  are  absorbed  by  the  roots  from  the  soil. 
Absorption  by  the  leaves  also  occurs  under  certain  circumstances  but 
ordinarily  this  process  may  be  disregarded.  The  water  relations  of 
plants  have  been  treated  in  the  previous  section;  the  other  plant  nutrients 
absorbed  from  the  soil  form  the  subject  of  this  chapter. 

DISTRIBUTION  OF  ELEMENTS  FOUND  IN  ASH 

The  mineral  constituents  of  plants,  except  a  part  of  the  sulfur,  are 
left  as  ash  after  the  tissue  has  been  burned.  Some  conception  of  the 
amount  and  composition  of  plant  ash  may  be  derived  from  the  analyses 
of  the  wood,  bark  and  leaves  of  the  beech  in  Table  1. 


Table  1. — Ash  Analyses  of  Wood,  Bark  and  Leaves  of  Beech"* 


Ash       K2O 

CaO 

MgO 

FeaOs 

P2O5 

SO3 

Si02 

Wood 

Bark 

Leaves 

0.355 
5_J60 
5.140 

14.4 

5.1 

21.8 

69.2 
88.4 
44.3 

4.5 
3.6 

7.2 

2.3 
0.7 
2.3 

2.7 
2.1 

7.8 

3.5 
1.0 

2.4 

10.0 
3.7 
10.5 

In  Tissues  of  Different  Kinds. — The  data  in  Table  2  on  the  amount 
and  composition  of  the  ash  of  apple  trees,  give  an  idea  of  the  variations 
that  maj^  occur  in  the  composition  of  different  parts.  The  distribution 
of  ash  in  the  apple  tree  at  the  time  of  leaf  fall  is  shown  in  Table  3.  The 
ash  percentage  of  bark  is  always  many  times  that  of  the  wood  as  Table  4 
shows.  The  ash  content  of  seeds  varies  from  2  to  6  per  cent.  Thus, 
seeds  of  the  chestnut  contain  2.38  per  cent,  of  ash,  almonds  4.9  per  cent, 
and  coffee  3.19  per  cent.^  The  composition  of  such  ash  appears  from 
data  presented  in  Table  5. 

101 


102 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 
Table  2. — Ash  Analyses  of  Apple  Varieties^*" 


Ash  in 
percent- 
ages of 
dry  weight 


Si02      P2O6      SO3      CaO     MgO    NaaO     K2O 


(In  percentages  of  ash) 


Branches : 

Haas 

Golden  Sweet 
Hurlburt 

Trunks: 

Haas 

Golden  Sweet 
Hurlburt 

Roots : 

Haas 

Golden  Sweet 
Hurlburt 


3.93 
3.04 
4.92 

2.04 
2.29 

2.89 

5.64 
3.53 
4.34 


1.81 

7.35 

3.02 

43.68 

10.02 

2.51 

2.49 

5.89 

2.96 

40.60 

8.07 

7.09 

2.60 

4.44 

3.57 

41.55 

2.88 

4.98 

2.04 

2.13 

7.55 

44.52 

9.30 

1.33 

4.98 

4.61 

1.17 

41.96 

4.61 

3.91 

3.93 

4.08 

3.85 

44.80 

5.22 

2.48 

26.84 

9.44 

5.11 

32.98 

9.30 

4.74 

27.65 

7.71 

2.83 

26.99 

4.84 

3.87 

25.72 

4.17 

6.19 

25.20 

10 .  37 

7.22 

8.59 
3.37 
5.16 

6.96 
8.02 
1.31 

5.43 
2.00 
9.86 


Table  3. — Ash  Analyses  of  a  7-year  Old  Apple  Tree  at  the  Time  of  Leaf-fall^^ 
(In  percentages  of  dry  weight) 

Summer  growth 3 .  57 

1-year  old  branches 2 .  83 

2-year  old  branches 2 .  76 

3-year  old  branches 2 .  75 

4-year  old  branches 1 .  87 

5-year  old  branches 1 .  78 

Trunk 1.33 

Large  roots =  .  .  .  .  1 .  83 

Small  roots 4.51 


Table  4. — Ash  Content  of  Wood  and  Bark® 
(In  percentages  of  dry  weight) 


Wood 


Mahaleb  cherry 
Sweet  cherry .  .  . 
Horse  chestnut . 


1.38 
0.23 

2.58 


Table  5. — Ash  Analyses  of  Seeds^" 


K2O 

CaO 

MgO 

P2O5 

SO3 

Chestnut 

56.6 
26.5 

3.8 

8.4 

7.4 
16.1 

18.1 
34.8 

3.8 

Plum ! 

7.1 

PLANT  NUTRIENTS  AND  THEIR  ABSORPTION 


103 


In  Tissues  of  Different  Age. — Age  is  likewise  an  important  factor 
influencing  ash  content.  The  percentage  of  ash  increases  with  age  in 
the  leaves  and  wood,  but  diminishes  in  the  roots,  branches  and  fruit. 
Though  in  these  last  it  increases  in  absolute  amount,  the  proportion  falls 
off  since  organic  matter  increases  at  a  greater  rate.  Table  6  shows  the 
increase  in  ash  content  of  beech  wood  with  age. 

Table  6. — Ash  Content  of  Beech  Wood^os 
(In  percentages  of  dry  weight) 


Years  of  Rings 
1  to  15 
15  to  25 
25  to  35 
35  to  45 
45  to  60 
60  to  83 
83  to  94  (sap-wood) 


1.162 
0.825 
0.645 
0.612 
0.555 
0.458 
0.205 


At  Different  Seasons. — An  increase  in  the  percentage  ash  content 
of  apple,  pear,  cherry  and  plum  leaves  during  the  season  is  shown  in 
Table  7.  The  absolute  amount  of  ash  present  declines,  however,  before 
the  leaves  fall  (Table  8).     Developing  fruits,  on  the  other  hand,  show  a 

Table  7. — Ash  Content  of  Leaves^^^  (in  percentages  of  dry  weight) 


Apple 

Pear 

Cherry 

Plum 

May  9 

8.304 

8.017 
9.166 

10.889 

6.908 



7.157 
9.454 

9.552 

9.006 

10.510 
12.319 

14.446 

May  14 

May  18 

June  22             . 

7.369 
15.031 

Aug.  29 

Sept.  30 

Oct.  2 

17.757 
20 . 987 

Oct.  15 

Table 

8.— C 

RAMS  OF  Ash 

IN  100  Leaves'*'^ 

Apple                  Pear 

Cherry 

Phun 

Ash 

Fresh 
weight 

Ash 

Fresh 
weight 

Ash 

Fresh 
weight 

Ash 

Fresh 
weight 

Julv  14 

2.876 
3.016 
3.576 
3.214 

95.15 
89.60 
95.10 
91.81 

1.270 
1.469 
1.548 
1.638 

47.19 
46.73 
42.98 
42.93 

2.494 
2.568 
2.814 
2.920 
3  214 

76.48 
64.73 
65.83 
64.98 
74   61 

3.038 
2.721 
2.693 

2.822 

3.076 

70  07 

Julv  31     

59.73 

Aug.  18,  21 

49.67 

Sept.  3,  4,  6 

50.20 

Oct.  7 

Oct.  23,  27,  29 

1.311 

36.22 

2.215    52.97 

55  85 

Nov.  4 

2.541 

66.46 

104 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


decrease  in  the  percentage  of  ash  and  an  increase  in  the  absolute  amount. 
The  data  in  Table  9  illustrate  these  changes.     The  large  increase  in  the 


Table  9. — Ash  Content  of  Fruit'^'' 


Pear 


Apple 


Date 

Percent- 
age of  dry 
weight 

Absolute 

amount, 

grams 

Date 

Percent-       Absolute 

age  of  dry      amount, 

weight           grams 

May  26 

7.96 
5.50 
4.32 
2.87 
3.27 
2.73 
.   2.27 
1.76 
1.46 
1.56 
0.91 
,,3I 

.0.0017 
0.0068 
0.0198 
0.0269 
0.043 
0.057 
0.069 
0.068 
0.079 
0.098 
0.065 
0.090 

June  2 

8.88 

0.0019 

June  12 

5.09 
3.44 
2.89 
1.80 
1.33 
1.78 
1.43 
1.33 
1.07 
0.80 
1.67 
1.58 

0.0066 

June  15 

June  22   

0.011 

June  25 

July  2 

July  12 

July  22 

Aug.  1 

0.026 

July  5 

0.034 

July  15 

0.044 

July  25 

0.070 

Aug.  11 

Aug.  21 

Aug.  31 

Sept.  10 

Sept.  20 

Sept.  30 

0.075 

Aug.  14 

0.076 

Aug   24 

0.079 

Sept  3 

0.066 

Sept   8 

0.160 

0.150 

ash  content  of  the  fruit  affects  the  ash  content  of  the  spur  on  which  the 
fruit  is  borne.     Figure  10  shows  a  rapid  decrease  in  the  percentage  ash 


Fig.  10. — Ash  content  of  apple  spurs  in  percentages  of  dry  weight;  bearing  spurs 
represented  by  continuous  lines  marked  W,  B  and  /  for  Wealthy,  Ben  Davis  and  Jonathan 
respectively;  non-bearing  spurs  shown  by  broken  lines  marked  J  and  B;  barren  spurs 
represented  by  dot-dash  lines  marked  B  and  A''  for  Ben  Davis  and  Nixonite.  {After 
Hooker.^oo) 

content  of  bearing  spurs  beginning  the  latter  part  of  May  or  in  June 
and  continuing  until  the  fruit  is  picked. i""  In  a  summer  apple  Hke 
Wealthy,  the  curve  rises  in  September,  the  fruit  having  been  picked  in 


PLANT  NUTRIENTS  AND  THEIR  ABSORPTION  105 

August.  In  Ben  Davis  and  Jonathan,  the  fruit  of  which  is  picked  the 
beginning  of  October,  the  curve  does  not  rise  until  November.  Spurs 
in  the  off  year  and  barren  spurs  have  no  such  characteristic  decrease 
in  ash  content  during  June. 

ABSORPTION 

Mineral  constituents  and  nitrogen  are  absorbed  by  the  plant  mostly 
through  the  roots.  They  are  present  in  the  soil  as  salts  in  solution  and 
are  taken  up  in  large  part  by  osmosis  along  with  the  soil  water,  the 
osmotic  system  being  the  same  as  that  involved  in  water  absorption. 

The  Osmotic  System. — The  soil  solution  and  the  cell  sap  are  sepa- 
rated by  a  semi-permeable  membrane,  through  which  the  salts  present  in 
the  soil  solution  are  able  to  enter  though  the  organic  substances  within  the 
cell  are,  for  the  most  part,  incapable  of  passing  in  the  opposite  direction. 
Inorganic  salts  dissociate  to  a  considerable  degree,  so  that  in  a  solution  of 
sodium  chloride,  for  example,  there  are  present,  besides  molecules  of 
salt,  ions  of  sodium  and  ions  of  chlorine.  These  separate  ions  have  the 
same  value  in  regard  to  osmotic  concentration  as  entire  molecules; 
consequently  a  solution  of  inorganic  salts  is  capable  of  producing  a  higher 
osmotic  pressure  than  a  solution  of  organic  compounds  having  the  same 
number  of  molecules  in  a  given  volume.  In  order  that  absorption  of  the 
various  mineral  constituents  should  take  place  by  osmosis,  the  concentra- 
tion of  each  salt  within  the  plant  must  be  less  than  its  concentration  in 
the  soil  solution.  Though,  as  previous  analyses  have  shown,  plant 
tissue  contains  considerable  amounts  of  these  mineral  elements  the  plant 
is  still  able  to  absorb  material  from  an  exceedingly  dilute  soil  solution 
which,  in  many  cases,  contains  a  lower  percentage  of  a  given  constituent 
than  the  plant  tissue  itself.  This  is  possible  because  the  constituents  in 
the  plant  are  insoluble  or  are  combined  in  an  organic  form.  Since  in 
either  case  they  are  removed  from  the  osmotic  system,  the  effective  con- 
centration of  inorganic  salts  within  the  plant  remains  less  than  that  of 
the  soil  solution.  It  is  evident,  though,  that  a  certain  concentration  of 
salts  in  the  soil  is  necessary  for  osmotic  absorption.  In  other  words,  the 
plant  is  unable  to  avail  itself  of  all  the  mineral  matter  of  the  soil  solution. 
However,  very  dilute  solutions  are  often  sufficient  for  ordinary  growth. 

Thus  "Birner  and  Lucanus  many  years  ago  found  that  mature  crops  of  good 
yield  could  be  grown  in  a  well  water  containing  about  18  parts  potassium  (K) 
and  about  2  parts  phosphoric  acid  (PO4)  per  million  of  solution  and  very  satis- 
factory'' growth  of  wheat  has  been  obtained  in  the  water  from  the  Potomac 
River,  which  contained  about  7  parts  per  million  of  potassium. "^^ 

When  these  facts  are  combined  with  the  conclusions  reached  by 
Cameron  and  Bell,^*  that  the  concentration  of  the  soil  solution,  with 
respect  to  the  principal  mineral  plant  nutrients,  is  sufficient  for  the  growth 


106  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

and  development  of  crops  and  that  the  magnitude  of  the  concentration 
is  the  same  for  practically  all  soils,  one  might  easily  be  led  to  the  belief 
that  fruit  plants  seldom  suffer  from  lack  of  an  adequate  supply  of  mineral 
nutrients.  However,  this  inference  is  hardly  warranted  for,  as  is  shown 
later,  mineral  nutrients  may  be  in  solution  and  still  be  unavailable  to  the 
plant.     In  other  words  solubility  and  availability  are  not  synonymous. 

Furthermore,  it  may  be  noted  that  the  5  parts  of  water  soluble  nitrates 
per  million  of  dry  soil  found  by  Gom-ley  and  Shunk^^  in  sod-mulched  orch- 
ards during  the  growing  season  were  apparently  insufficient  for  satisfactory 
wood  growth  and  fruit  production,  while  a  concentration  of  15  to  40  parts 
per  million  under  certain  other  systems  of  culture  proved  entirely  ade- 
quate. In  this  case  all  the  nitrogen  measured  was  in  an  available  form. 
Whether  in  the  sodded  area  nitrogen  could  be  absorbed  by  the  trees  only 
when  the  concentration  in  the  soil  reached  a  certain  minimum,  or  whether 
a  very  limited  amount  was  absorbed  even  at  the  lowest  concentrations, 
cannot  be  stated  from  available  data;  they  show  clearly,  however,  that 
the  trees  were  unable  to  remove  nitrates  completely  from  the  soil  and 
further,  that  a  nutrient  solution  very  dilute  in  respect  to  this  element 
provides  only  for  very  slow  growth. 

Displacement. — The  amounts  of  the  various  inorganic  constituents 
in  the  soil  are  subject  to  variation  and  exchanges  of  bases  may  occur  when 
they  are  present  as  silicates.  Potassium,  ammonium,  magnesium, 
sodium  and  calcium  form  a  series  in  which  each  member  is  capable  of 
displacing  any  member  following  it  in  the  series.  One  of  two  things 
may  happen:  an  essential  element  may  be  lost  to  the  plant  by  becoming 
soluble  and  being  washed  out  of  the  soil,  or  it  may  be  changed  from  an 
unavailable  to  an  available  compound  and  so  placed  at  the  disposal  of 
the  plant. 

Of  most  common  occurrence  is  the  displacement  of  calcium  by 
potassium  or  sodium,  resulting  in  the  calcium  salts  going  into  solution. 
However,  large  amounts  of  calcium  are  capable  of  displacing  small 
amounts  of  potassium ^''^  or  any  other  base  standing  ahead  of  it  in  the 
series.  Hence,  calcareous  soils  are  likely  to  be  deficient  in  potash 
and  the  application  of  calcium  in  great  amounts  tends  to  deplete  the 
potassium  supply.  Grape-fruit  seedlings  have  been  observed  to  show 
injuries  characterized  by  yellowing  of  the  foliage  due  apparently  to 
the  presence  of  ground  limestone;  more  injury  was  evident  in  sandy 
soils  than  in  loams. ^®  One  type  of  this  yellowing  is  "frenching,"  a 
lack  of  green  color  in  the  areas  between  the  largest  veins,  which  is  shown 
later  to  be  a  characteristic  symptom  of  potassium  starvation.  "French- 
ing"  was  produced  also  by  sulphate  of  ammonia  or  organic  fertilizers 
containing  ammonia.  This  effect  may  be  attributed  to  displacement 
of  potassium  in  the  soil  by  relatively  large  amounts  of  ammonia. 

The  effects  on  the  plant  of  displacement  of  bases  may  be  indirect 


PLANT  NUTRIENTS  AND  THEIR  ABSORPTION  107 

rather  than  direct,  for  the  displacement  elements  may  combine  to  form 
more  soluble  salts  and  thus  be  rendered  more  available. 

As  an  instance,  according  to  Loew:^-*  "Lime  and  gypsum  can  also  in  cer- 
tain cases  release  such  potash  in  the  soil  as  is  still  unavailable.  This,  as  well  as 
the  enhanced  root-hair  production  under  the  influence  of  the  increased  amount 
of  ume,  accounts  for  the  greater  absorption  of  potash  by  the  plant  on  soils  rich 
in  lime." 

Displacement  would  of  course  be  of  little  value  to  the  plant  if  the 
elements  released  were  washed  from  the  soil  as  a  result  of  the  greater 
solubility  of  their  salts. 

Availability  of  Ash  Constituents. — The  soil  constituents  are  of  use 
to  the  plant  only  when  combined  in  certain  specific  chemical  compounds. 
Thus,  sulphur  must  be  present  as  sulphate,  phosphorus  as  phosphate,  and 
the  various  bases  as  relatively  soluble  salts. 

Availability  and  Solubility  Distinguished. — Solubility,  however,  is 
only  the  first  prerequisite  to  availability  and  absorption;  it  is  not  an 
absolute  criterion  of  the  crop-producing  power  of  soils,  as  is  indicated  by 
studios  on  many  soils  in  this  country^^  and  by  investigations  on  the  red 
soils  of  the  "djati"  forests  of  Java.^^  Nevertheless,  "in  general  it  can 
be  said  that  a  very  heavily  fertilized  or  extremely  rich  soil  gives  a  greater 
solubility  product  than  an  unfertilized  or  poor  soil."^^  Conversely 
"as  a  result  of  laboratory  studies  it  appears  that  the  constituents  of 
soils  which  have  been  cropped  for  a  long  period  of  years  go  into  solution 
at  a  somewhat  slower  rate  than  do  those  of  the  corresponding  virgin 
soils. "^^'^ 

Factors  Influencing  Solubility. — The  solubility  of  soil  ingredients  is 
affected  by  such  factors  as  temperature,  moisture  content,  chemical 
composition  of  the  soil  and  root  activity.  According  to  McCool  and 
Millari3o  the  rate  of  solution  is  more  rapid  at  25°C.  than  at  0°C.  The 
concentration  of  the  soil  solution  apparently  depends  also  on  the 
relative  masses  of  the  soil  and  water. 

"At  the  ratio  of  1  of  soil  to  5  of  water  the  rate  of  solubility  of  natural  soils 
is  also  slow  and  the  extent  of  solubility  extremely  small.  In  fact,  the  amount  of 
material  that  went  into  solution  at  this  water  content  is  only  about  half  as  much 
as  that  at  the  water  content  of  1  of  soil  to  .7  of  water,  and  yet  an  apparent 
equilibrium  was  attained.  .  .  .  The  amount  of  material  that  goes  into  solution 
seems  to  increase  as  the  ratio  of  soil  to  water  is  increased  up  to  about  the  opti- 
mum moisture  content  and  then  it  decreases."^* 

The  effect  of  chemical  composition  on  solubility  is  discussed  by 
Bouyoucos.^^ 

"As  a  whole  it  appears  that  the  phosphates  tend  to  depress  solubihty  and  that 
they  probably  act  as  conservers  of  bases  under  field  conditions."     Other  salts, 


108 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


however,  tend  to  increase  solubility.  "The  result  of  solubility  of  these  singly 
salt  treated  soils  goes  to  indicate  that  a  salt  or  fertilizer  treatment  leaves  a  resid- 
ual effect  upon  the  soil  and  this  residual  effect  continues  to  be  manifested  in  in- 
creased solubility  and  in  increased  crop-producing  power." 

Availability  of  Phosphorus. — It  has  been  stated  that  phosphorus 
is  available  to  the  plant  only  when  present  as  a  phosphate  and  that  sul- 
phur is  absorbed  only  as  sulphate.  However,  all  phosphates  and  sulphates 
are  not  equally  available;  furthermore,  a  phosphate  that  is  highly  avail- 
able for  the  plants  of  one  species  may  be  much  less  available  to  those  of 
another.  This  principle  is  well  illustrated  by  the  data  presented  in 
Table  10  showing  the  percentage  of  normal  growth  made  by  plants  grown 
in  nutrient  solutions  that  were  uniform  except  for  the  form  in  which 
phosphorus  was  presented. 

Table  10. — Comparative  Growth  of  Various  Plants  with  Different 
Phosphates 
(After  Truog^^^) 
(Growth  on  acid  phosphate  represented  by  100) 


Kind  of 
plant 

Kind  of  phosphate 

Blank 

Alumi- 
num 

Tri- 
calcium 

Ferric 

Ferrous 

Rock 

Mag- 
nesium 

Man- 
ganese 

Oats 

Buckwheat.  . 

Rape 

Corn 

Barley 

Alfalfa 

Clover 

Millet 

Serradella.  .  . 

6.8 
3.6 
0.8 
8.6 
16.7 
1.5 
1.0 
0.7 
0.6 

96.4 

88.0 

96.4 

56.3 

104.7 

78.6 
84.2 
86.7 

78.7 

70.5 
70.1 
76.2 
26.8 
62.2 
99.2 
64.5 
34.8 
90.4 

79.9 
32.5 
23.4 
40.3 
133.5 
93.6 
68.9 
103.8 
111.7 

82.9 
63.3 
61.5 
19.3 
79.7 
28.1 
23.6 
31.0 
28.2 

9.1 

70.0 

46.8 

10.0 

25.8 

38.3 

6.1 

4.1 

3.2 

21.3 
15.5 
7.1 
26.7 
16.0 
49,9 

76.4 
125.3 
20.8 
4.2 
73.8 
51.7 

In  commenting  on  these  data  Truog'*^  remarks:  "The  great  differences 
exhibited  by  the  various  plants  in  their  growths  on  the  different  phosphates 
indicate  tliat  plant  characteristics  play  an  important  role  in  this  connection. 
The  fact  that  rape  made  a  better  growth  on  rock  phosphate  than  on  ferric 
phosphate,  while  in  the  case  of  oats  the  opposite  was  true,  indicates  that  solu- 
biUty  alone  is  not  the  only  factor  involved  in  the  utilization  of  these  phosphates 
by  plants.  The  remarkably  vigorous  growth  of  the  barley  with  ferric  phos- 
phate is  another  indication  that  aside  from  solubility  or  availabiUty,  some 
phosphates  seem  to  serve  the  needs  of  certain  plants  better  than  others.  The 
remarkable  adaptability  of  certain  soils  to  certain  crops  may  partly  be  due  to 
causes  of  this  nature." 

Availability  Varies  According  to  Kind  of  Plant. — In  general  the  avail- 
ability of  inorganic  soil  constituents  is  increased  by  the  activity  of  the 


PLANT  NUTRIENTS  AND  THEIR  ABSORPTION  109 

roots.  Their  solvent  action  is  yet  to  be  accounted  for  satisfactorily. 
Crocker  suggests  that  the  strong,  insoluble  pectic  acids  found  in  the 
walls  of  root  hairs  may  be  responsible  for  the  absorption  of  bases  and 
the  setting  free  of  mineral  acids,  which  would  have  a  localized  and 
temporary  solvent  action  on  the  soil.  Various  plants  show  great  differ- 
ences in  the  dissolving  power  of  their  roots,  or  at  least  in  their  ability  to 
obtain  required  nutrients. 

Hartwell*^  found  that  carrots  secured  all  the  phosphorus  they  required  from 
a  soil  in  which  rutabagas  and  cabbage  were  practically  unable  to  grow,  while 
wheat,  oats,  white  beans  and  soy  beans  ranged  between  these  extremes.  Simi- 
larly, he  found  "an  ability  of  the  soy  bean  to  obtain  from  the  deficient  [in  avail- 
able potassium]  plots  about  two-thirds  of  their  maximum  requirements,  whereas 
carrots  obtained  about  half  their  needs,  mangels  about  one-fourth  and  summer 
squash  only  about  one-tenth." 

It  is  not  clear  to  what  extent  this  characteristic  feeding  power  of 
various  plants  may  be  due  to  varying  ability  to  dissolve  the  materials 
they  encounter  in  a  solid  or  colloidal  form,  what  part  may  be  due  to 
varying  ability  to  use  nutrients  combined  in  different  forms  (e.g.,  potas- 
sium in  the  form  of  a  chloride  instead  of  sulphate),  or  what  part  may  be 
due  to  varying  ability  to  absorb  from  very  dilute  solutions.  This 
question  needs  careful  investigation,  particularly  in  its  application  to 
orchard  and  vineyard  fruits  of  different  kinds  and  to  the  stocks  upon 
which  they  may  be  grown.  It  is  conceivable  that  the  high  feeding  power 
of  a  certain  stock  in  respect  to  some  particular  material  may  be  of  as 
great  significance  in  the  success  of  a  fruit  plantation  in  a  certain  soil 
as  the  question  of  "congeniality"  of  stock  and  cion.  From  the  data 
presented  by  Hartwell,  the  inference  may  .be  drawn  that  the  potassium 
found  in  the  soil  and  practically  unavailable  to  mangels  and  summer 
squash  would  be  made  available  to  them  were  soy  beans  first  grown 
upon  the  land  and  then  plowed  under,  for,  after  the  soy  beans  had 
dissolved  and  used  it,  other  plants  wovild  find  it  in  a  different  form. 
There  may  be  little  occasion  for  special  efforts  to  make  potash  more 
available  to  orchard  trees  by  using  intcrcultures,  for  evidence  is  presented 
later  that  for  fruit  trees  potash  is  seldom  a  limiting  factor.  Nevertheless, 
the  general  principle  involved  may  be  important  in  relation  to  other 
elements. 

Availability  of  Iron  and  Sulphur. — Certain  types  of  bacteria  oxidize  sulphur  or 
hydrogen  sulphide  to  sulphates  and  others,  ferrous  oxide  to  ferric  oxide.  These 
organisms  may  play  some  part  in  rendering  sulphur  and  iron  available,  though 
the  most  important  type  of  bacterial  action  in  the  soil  is  concerned  with  general 
decomposition  and  particularly  with  the  nitrogen  supply. 

Availability  of  Nitrogen. — Just  as  sulphur  is  available  only  in  the  form 
of  sulphate  and  phosphorus  in  the  form  of  phosphate,  most  nitrogen  is 


no  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

absorbed  in  the  form  of  nitrate.  However,  nitrites  and  salts  of  ammonia 
can  be  utilized  to  a  limited  extent,  different  plants  showing  considerable 
variations  in  this  respect.  Organic  nitrogen  also  may  be  a  substitute  for 
nitrate,  though  inorganic  nitrogen  compounds  are  used  in  preference. 
It  has  been  shown  that  such  nitrogenous  soil  constituents  as  nucleic 
acid,  hypoxanthine,  xanthine,  guanine,  creatinine,  creatine,  histidine, 
arginine  and  choline  serve  as  sources  of  nitrogen  when  nitrates  are  absent, 
but  not  to  any  great  extent  when  large  amounts  of  nitrate  are  pres- 
gjj^  163,  169.  Moreover,  the  absorption  of  nitrate  by  plants  grown  in 
culture  is  always  reduced  when  creatine  or  creatinine  is  present,  though 
the  total  nitrogen  intake  remains  fairly  constant.  These  organic  nitrogen 
compounds  have  no  effect  on  potash  or  phosphorus  absorption. 

Bacteria  are  of  great  importance  in  making  organic  nitrogen  com- 
pounds in  the  soil  more  available  to  the  plant  and  incidentally  in  destroy- 
ing toxic  substances.  Putrefying  bacteria,  for  example,  convert  the 
nitrogen  of  organic  compounds  to  ammonia  and  nitrogen  gas. 

Hart  and  Tottingham*^  have  shown  that  "soluble  phosphates  increase 
enormously  the  number  of  soil  organisms  and  the  rate  of  ammonification  and 
destruction  of  organic  matter,  while  the  sulphates  activate  but  slightly  in  these 
directions.  The  processes  mentioned  are  admitted  to  be  of  great  importance 
to  the  plant's  nutrition  and  environment,  involving,  as  they  must,  not  only  a 
more  rapid  formation  of  readily  soluble  compounds  of  nitrogen  and  a  possible 
destruction  of  harmful  organic  materials,  but  a  greater  saturation  of  the  soil 
moisture  with  carbon  dioxide,  resulting  in  increased  solution  of  mineral  materials 
necessary  for  rapid  growth."  Work  at  the  Utah  Experiment  Station^^  indicates 
that  sulphates  have  a  particularly  stimulating  effect  on  soil  bacteria  under  certain 
conditions. 

Nitrification. — The  ammonia  produced  by  bacterial  action  is  in  its  turn 
converted  to  nitrites  and  these  nitrites  to  nitrates  by  nitrifying  bacteria, 
each  of  these  changes  being  carried  out  by  distinct  organisms.  These 
organisms  require,  for  the  process  of  nitrification,  good  aeration,  involving 
both  oxygen  and  carbon  dioxide,  a  certain  water  supply,  the  presence  of 
calcium  or  magnesium  compounds,  a  medium  temperature  and  freedom 
from  an  excess  of  soluble  organic  compounds  or  from  free  ammonia.  It 
is  evident  that  conditions  favoring  the  action  of  nitrifying  organisms  will 
tend  to  increase  the  supply  of  available  nitrogen. 

Aided  by  Liming.— It  has  been  found  that  applications  of  lime  in  many 
cases  increase  nitrification.  Table  11  presents  the  results  of  one  such 
experiment  with  orchard  soils  in  New  Hampshire.  Obviously  in  this 
instance  liming  benefited  the  soil  in  at  least  this  one  direction  and  it  is 
possible  that  at  the  same  time  it  exerted  no  harmful  influence.  However, 
data  are  presented  later  to  show  that  it  may  have  a  very  harmful  effect 
through  rendering  iron  unavailable.  Consequently  a  single  fertilizer 
application  may  produce  at  the  same  time  both  beneficial  and  harmful 


PLANT  NUTRIENTS  AND  THEIR  ABSORPTION 


111 


Table  11.— Nitrates  in  Limed  and  Unlimed  Plots  »i 

(In  parts  per  million  of  dry  soil) 

Limed  plot 

Unlimed  plot 

Year 

Surface  soil 

Subsoil 

Surface  soil 

Subsoil 

1913 

82.33 

19.60 

57.46 

6.16 

1914 

82.46 

23.43 

57.09 

15.21 

1915 

29.98 

13.78 

24.26 

17.24 

1916 

98.48 

24.16 

80.36 

11.56 

Average 

73.31 

20.23 

54.79 

12.54 

effects.  These  may  just  about  neutralize  each  other  and  leave  the  plants 
practically  uninfluenced  by  the  treatment,  or  the  one  influence  may 
greatly  outweigh  the  other.  Caution  should  be  exercised,  however,  in 
making  applications  of  lime  to  the  orchard. 

Influenced  by  Methods  of  Soil  Management. — Moreover  different 
methods  of  soil  management,  particularly  as  they  effect  aeration  and  soil 
temperature  have  a  marked  effect  on  nitrate  production. 

Gourley  and  Shunk*'  found  that  "the  ratio  of  nitrates  between  sod,  tillage 
and  tillage  with  cover  crops  is  as  1  :  5.4  :  10.6  in  the  surface  soil  and  in  the  sub- 
soil as  1  :  3.3  :  3.7.  At  no  time  during  the  experiment  have  we  obtained  a 
sample  under  sod  that  showed  more  than  14.78  parts  nitrates  per  million  and  the 
average  for  the  4  years  is  3.18  p. p.m.  with  an  average  of  17.40  p. p.m.  and  for 
tillage  plus  a  leguminous  cover  crop  it  has  shown  as  high  as  132  p.p.m.  and  the 
average  is  33.91  p.p.m.  for  the  4  years." 

The  nitrate  determinations  showing  the  result  of  4  years'  experiments 
on  orchard  soils  are  summarized  in  Table  12,  Whether  the  small 
amount  of  nitrate  under  sod  is  the  result  of  reduced  nitrate  produc- 
tion or  merely  the  residue  from  a  greater  nitrate  consumption  by  the 
plants  constituting  the  sod,  the  effect  on  the  orchard  trees  is  the  same. 
Under  sod  there  is  but  little  available  nitrate.  In  Indiana  also,  it  was 
found  that  in  a  young  orchard  most  nitrates  are  formed  under  the  clean 
culture-cover  crop  system  of  soil  management,  and  the  straw  mulch 
ranked  next.-"*^  The  heavier  the  mulch,  the  later  in  the  spring  does 
bacterial  activity  begin  because  of  the  lower  temperature  and  the  later 
in  the  fall  does  it  persist  as  a  result  of  the  higher  temperature  of 
the  soil. 

It  is  probably  because  of  their  influence  upon  nitrate  formation  that 
various  tillage  methods  have  so  generafly  proved  superior  to  sod  manage- 
ment methods  in  promoting  both  vegetative  growth  and  fruit  production. 
This  is  true  particularly  in  areas  that  are  more  humid  or  have  deeper 
soils.     On  the  other  hand,  in  sections  having  a  long  dry  period  during 


112 


FlXDAMEXTAl.S  OF  FRVIT  rRODlCTIO.X 


TaBI.K    V2. WaTKK    Soi.lBl.E    XlTKATE    IN     PaHTS    TEK    Mll.LlON    OK    DuY    SoIL" 

i,.\voi;igo  por  \i\oO 


Year 


Sod 


Surfaoo  soil 


Tillage 


I'illago  with  oovor 
crop 


1913 
1914 
1915 
1916 


Averngo 


4  41 
2  00 
o  59 

3.  IS 


IS.  25 
14.01 
21.05 
16.29 

17.40 


oS .  o< 
37  27 
IS  75 
41.20 

33.01 


Subsoil 


1913 

1 .  55 

6.90 

0  S7 

1914 

3  56 

6.62 

10.  SI 

1915 

1.51 

10.76 

6.SS 

1916 

2. IS 

5.05 

S  05 

Averasro 

2  20 

7.33 

S  15 

iho  sunmior.  wherever  the  soils  are  of  sueh  nature  that  they  encourage 
shallow  rooting  the  iuHuenee  of  these  various  systems  of  soil  management 
iipcMi  moisture  supply  is  probably  a  factor  of  equal  or  greater  unportance. 
However,  it  is  neither  difficult  nor  expensive  to  furnish  trees  growing  in 
sod  with  an  adequate  supply  of  nitrates  through  the  use  of  certain  fertil- 
izers. Indeed,  it  is  in  orchards  of  this  kind  that  nitrogenous  fertilizers 
have  given  some  of  the  most  striking  results  and  the  question  maj-  be 
raised  whether  some  nitrogen-carrying  fertilizer  may  not  be  a  more  or 
less  constant  requirement  if  orchards  permanently  under  this  method  of 
soil  management  are  to  be  kept  growing  and  producing  most  efficiently. 

Influt'wecl  by  Temperature  and  Soil  Moisture. — The  effects  of  moisture 
and  of  temperature  on  the  activity  of  nitrifying  bacteria  are  shown  by  a 
seasonal  variation  in  nitrate  content.  For  example,  in  Illinois  soils -^'' 
the  most  active  season  of  nitrate  production  and  accumulation  is  late 
spring  and  early  summer  when  optimum  moisture  and  temperature 
conditions  are  approached.  Early  autumn  is  the  next  most  active 
season,  when  these  optimum  conditions  for  nitrate  production  are  fre- 
quently approached.  During  the  summer  little  nitrate  is  produced 
unless  the  weather  is  cool  and  moisture  plentiful;  in  winter  there  is  no 
evidence  of  nitrate  production. 

Similar  conditions  are  i-eported  for  orchard  soils  in  Indiana^^  where 
very  little  nitrate  was  found  in  late  fall  and  winter,  though  maxima  were 
found  in  early  summer  and  early  fall.     Orcharding,  however,  is  carried 


PLANT  NUTItlKNTS  AND  TIIEIli  AHSOIil'T ION  1]:^ 

on  in  inany  scMrtioiis  where  seasonal  and  soil  conditions  an;  iriat(!i'ially 
dilferent  from  thoso  of  Illinois  and  Indiana  antl  it  is  concoivabh;  lliat 
under  Certain  environinontal  conditions  nitrate  production,  evcni  under 
sod,  inif2;ht  keep  pace;  wilh  the  tn^e's  requirements  for  nitrog(!n. 

Losses  of  Nitrogen  from  the  Soil. — Nitrates  are  very  soluble  in 
\vat(M-  ajid  unlike  most  of  the  mineral  nutrients,  are  not  adsorbed  or 
otherwise;  fixed  in  the  soil  to  any  considerable  degree.  Heavy  rains  or 
heavy  irrigation  washes  them  out  and  carries  them  away  in  the  drainage 
water.  In  one  Florida  experiment  this  loss  from  leaching  was  found  to 
('(pial  the  nitrate  content  of  over  800  pounds  of  nitrate  of  soda  per  acre 
during  a  10-month  period/  Not  the  least  important  function  of  cover 
crops  is  to  take  up  the  nitrates  that  are  being  formed  in  late  summer  and 
autumn,  to  store  their  nitrogen  in  organic  form  during  the  winter  and  to 
return  it  to  the  soil — thence  to  the  trees — the  following  growing  season, 
thus  preventing  a  large  loss  through  drainage.  The  advantage  of  a 
soil,  and  of  orchard  management  methods,  permitting  deep  rooting  and  the 
storage  of  large  quantities  of  capillary  water  minimizing  seepage  losses, 
is  evident. 

Maintaining  the  Nitrogen  Supply  of  the  Soil. — Despite  the  means 
that  may  be  taken  to  prevent  undue  loss  of  soil  nitrates,  crop  production 
alone  removes  considerable  quantities  and  unless  the  supply  of  nitro- 
genous coinpounds  from  which  they  arc  derived  is  maintained  the  time 
will  come  when  they  cannot  be  formed  in  quantities  sufficient  for  maxi- 
mum crop  production.  The  organic  matter  of  the  soil  is  the  storehouse 
of  these  nitrogenous  compounds  and  with  its  gradual  depletion  the 
nitrogen  problem  becomes  acute.  It  is  well  known  that  constant  tillage 
is  one  of  the  most  effective  means  of  reducing  or  "burning  out"  humus 
supply.  Consequently  the  cultural  methods  in  the  orchard  that  make 
nitrogen  available  most  rapidly,  deplete  the  total  supply  most  rapidly. 
Indeed  it  may  be  questioned  if,  over  a  long  period,  the  orchard  under  a 
strictly  clean-culture  method  of  management  will  not  need  heavier 
nitrogen  fertilization  than  the  one  in  sod. 

Some  measure  of  the  cumulative  effect  of  tillage  as  compared  with  a  sod 
covering  on  total  nitrogen  supply  is  contained  in  the  following  statement: 
"Analysis  of  soil  taken  from  this  land  at  the  time  the  experimental  work  was 
started  indicated  a  nitrogen  content  of  5,000  pounds  per  acre.  After  this  soil 
had  been  cropped  and  cultivated  for  20  years,  the  nitrogen  content  was  approxi- 
mately 4,000  pounds  per  acre.  Adjacent  soil  which  was  in  grass  during  the  20- 
year  period  contained  5,600  pounds  of  nitrogen."^  It  is  significant  that,  though 
there  was  a  loss  of  20  per  cent,  of  the  total  nitrogen  supply  of  the  soil  during  the  20 
years  in  the  cultivated  land,  there  was  an  actual  increase  of  12  per  cent,  in  the 
sod  land  during  the  same  period.  This  can  be  attributed  to  nitrogen  fixation, 
particularly  by  leguminous  plants  in  the  sod,  in  addition  to  the  nitric  acid 
contributed  by  rain  water. 

8 


114  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

The  likelihood  of  trees  under  one  of  the  two  standard  systems  of 
orchard  culture  suffering  from  lack  of  available  nitrogen  and,  on  the  other 
hand,  the  nearly  absolute  certainty  that  under  the  other  system  the 
soil  will  have  its  total  nitrogen  I'eserve  seriously  depleted,  suggest 
that  a  combination  of  the  two  methods  possibly  might  afford  a  means  of 
maintaining  permanently  the  nitrogen  supply  of  the  soil  and  at  the  same 
time  obviate  the  necessity  of  supplying  the  trees  artificially  with  readily 
available  nitrates.  Such  a  combination  might  consist  in  alternating 
sod  and  cultivation  each  in  2-year  periods  or,  better  still,  in  maintaining 
alternate  tree  rows,  the  "middles,"  under  the  two  respective  systems 
and  then  occasionally  reversing  the  treatments  on  these  alternate  strips. 
The  marked  success  that  frequently  has  attended  such  a  combination  is 
evidence  of  its  practicability  under  many  conditions.  Such  a  combina- 
tion treatment  is  a  compromise  also  in  its  influence  upon  soil  moisture 
supply  and  soil  erosion.  In  some  instances  it  might  prove  undesirable 
because  of  the  increased  difficulty  in  controlling  certain  orchard  pests 
which  are  best  held  in  check  by  cultivation. 

Few,  if  any,  of  the  plant  nutrients  obtained  from  the  soil  are  subject 
to  such  great  variation  from  season  to  season  and  even  from  week  to 
week  as  is  nitrogen;  likewise  few  are  so  completely  under  the  control  of 
the  grower  through  methods  of  soil  management.  It  is  largely  because  of 
the  first  two  facts  that  the  problem  of  maintaining  fertility  in  the  orchard 
generally  centers  around  the  nitrogen  supply.  The  discussion  that  has 
preceded  serves  also  to  bring  out  clearly  the  fact  that  proper  treatment 
of  the  soil  may  reduce  or  altogether  remove  the  necessity  for  nitrogen 
fertilization  and  that,  on  the  other  hand,  there  are  instances  where  it  may 
be  true  economy  not  to  employ  those  practices  that  will  lead  to  greatest 
nitrate  formation  but  deliberately  to  limit  this  process  and  supply  the 
deficiency  by  artificial  means. 

Nitrogen  Fixation. — Nitrogen  gas  is  not  available  to  the  higher  plants, 
but  it  is  acted  upon  by  nitrogen-fixing  bacteria  which  convert  it  either 
to  nitrates  or  to  other  nitrogenous  compounds  that  in  due  time  are  con- 
verted into  nitrates.  Some  of  these  bacteria  are  able,  independent  of  any 
association  with  the  roots  of  higher  plants,  to  fix  this  atmospheric  nitro- 
gen and  thus  effect  the  first  step  in  rendering  it  available.  ^^' ^^  Indeed 
there  are  conditions  under  which  their  activity  is  so  great  that  the  resul- 
tant accumulation  of  nitrates  renders  the  soil  toxic  to  trees  and  other 
plants.^'  For  the  most  part,  however,  nitrogen  fixation  by  bacteria 
is  effected  by  forms  living  in  colonies  on  the  roots  of  leguminous  plants 
where  they  produce  nodules  or  tubercles. 

As  very  few  of  the  species  bearing  edible  fruits  belong  to  the  legume 
family,  nitrogen-fixing  bacteria  are  of  comparatively  little  direct  benefit 
except  when  they  fix  nitrogen  in  the  absence  of  host  plants.  However, 
they  become  of  great  value  indirectly  when  leguminous  cover  crops  or 


PLANT  NUTRIENTS  AND  THEIR  ABSORPTION  115 

a  sod  including  legumes  is  maintained.  There  are  conditions  under 
which  it  is  difficult  or  impracticable  to  grow  legumes  in  the  orchard; 
nevertheless  their  special  value  should  not  be  overlooked,  particularly 
where  there  is  need  of  increasing  the  available  nitrate  supply.  Their 
judicious  use  in  place  of  some  of  the  other  cover  or  mulching  crops  or 
in  the  place  of  some  other  system  of  orchard  management  often  obviates 
the  necessity  of  supplying  the  trees  with  nitrogen  through  mineral  or 
animal  fertilizers. 

An  instance  of  the  results  that  can  be  obtained  by  the  use  of  leguminous  plants 
as  cover  crops  is  described  by  Coville.'*^  "  The  trees  in  one  newly  planted  orchard 
of  Grimes  apples  have  been  kept  in  a  remarkable  condition  of  growth  by  one 
initial  application  of  manure  in  the  year  of  their  planting,  succeeded  by  the 
following  rotation:  In  May  the  ground  is  sowed  to  cowpeas.  These  are  plowed 
under  in  September  and  followed  immediately  by  the  sowing  of  rye  mixed  with 
hairy  vetch.  In  the  following  May  the  mixed  crop  is  plowed  under.  The 
same  1-year  rotation  has  been  followed  year  after  year.  Under  this  treatment 
the  soil,  which  has  the  appearance  of  almost  pure  sand,  has  become  so  fertile 
without  the  application  of  lime,  commercial  fertilizer  or  manure  that  an  occa- 
sional crop  of  cowpeas  has  been  cut  for  hay  without  serious  interference  with  the 
progress  of  the  orchard."  The  successful  use  of  such  a  system  would  depend 
upon  an  abundant  water  supply. 

Were  it  possible  to  maintain  permanently  a  good  stand  of  clover, 
vetch,  alfalfa  or  some  other  leguminous  crop  in  the  orchard  and  to  leave 
the  growth  that  it  produced  on  the  ground  for  a  mulch,  it  would  afford 
an  almost  ideal  sod  system  of  management — from  the  standpoint  of 
maintaining  Soil  fertility — though  water  competition  between  the  trees 
and  the  intercrop  would  make  it  entirely  impracticable  under  many 
circumstances.  Under  average  conditions,  however,  the  maintainance 
of  such  a  sod  is  next  to  impossible  because  bluegrass  or  other  species 
crowd  out  the  legumes.  Where  such  a  legume  sod  can  be  maintained 
and  the  competition  for  moistm-e  can  be  largely  eliminated  by  irrigation, 
a  system  of  soil  management  is  possible  that  affords  the  trees  excellent 
nutritive  conditions  for  vigorous  growth  and  heavy  production  and  is 
at  the  same  time  economical.  Various  fungi  found  in  the  roots  of  certain 
heaths  (Ericaceae),  are  likewise  capable  of  fixing  nitrogen.  It  is  probable 
that  the  cranberry  and  blueberry  obtain  at  least  a  portion  of  their  nitro- 
gen supply  through  similar  agencies. 

Soil  Reaction :  Acidity  and  Alkalinity. — The  absorption  of  available 
inorganic  salts  by  the  root  is  affected  to  an  important  degree  by  acidity, 
concentration,  toxicity,  aeration  and  temperature  of  the  soil  and  of  the 
soil  solution.  The  reaction  of  the  soil  solution  is  of  great  importance. 
Most  plants  thrive  best  when  the  soil  is  very  weakly  acid.  Many  water 
plants  live  better  in  a  very  weakly  alkaline  solution,  while  land  plants 
show  marked  differences  in  the  amount  of  acidity  which  they  will  endure. 


116  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

When  the  acidity  of  the  soil  increases  beyond  the  low  value  which  is 
most  favorable  to  land  plants,  it  becomes  an  important  factor. 

Soil  Reaction  and  the  Availability  of  Phosphorus. — The  effect  of  soil 
acidity  on  the  availability  of  phosphorus  is  shown  by  the  following 
quotation  from  Harris  :^^ 

"In  addition  to  the  work  that  has  been  done,  on  determining  the  degree  of 
soil  acidity,  many  investigations  have  been  undertaken  to  determine  the  relation 
of  soil  acidity  to  the  quantity  of  available  phosphorus  in  the  soil.  As  a  result 
of  the  work  of  Wheeler,  Thorne,  Whitson  and  Stoddart,  it  has  been  show  that  the 
content  of  this  element  is  generally  low  in  acid  soils  and  largely  unavailable  for 
use  by  plants.  Stoddart  explains  this  by  saying  that  acid  soils  convert  any 
calcium  phosphate  that  may  be  present  into  soluble  compounds  which  are  either 
washed  out  or  are  fixed  in  an  insoluble  form  by  the  formation  of  iron  and  alumi- 
num phosphates." 

Soil  Reaction  and  the  Availability  of  Iron.- — An  excess  of  calcium  salts 
affects  the  availability  of  iron  in  such  a  way  that  many  plants  grown  on 
calcareous  soils  suffer  from  lack  of  iron,  even  though  iron  is  present  in 
considerable  amounts.  It  is  from  this  cause  that  grape  vines  and  fruit 
trees  become  chlorotic  on  some  of  the  calcareous  soils  of  France  and 
England,  pineapples  and  sugar  cane  on  Porto  Rican  soils  containing 
large  amounts  of  lime  and  citrus  fruits  in  Florida  when  ground  limestone 
is  added  to  the  soil. 

"In  Porto  Rico  the  extension  of  the  pineapple  industry  has  been  retarded 
by  a  disease  known  as  chlorosis,  the  principal  external  mark  of  which  is  the 
yellowing  of  the  foliage  and  the  consequent  poor  nutrition  of  the  plant.  From 
investigations  by  Gile  and  by  Loew  it  appears  that  the  yellow  color  of  the  leaves 
and  the  accompanying  weakness  of  the  plant  are  due  to  the  lack  of  iron,  and  that 
where  the  soil  contains  an  excess  of  lime  the  organic  acids  which  are  needed  to 
dissolve  the  iron  of  the  soil  are  themselves  neutralized  and  the  iron,  although 
present,  is  not  available  for  absorption  by  the  pineapple  roots. "^* 

According  to  Gile  and  Carrero,"  sugar  cane  grown  on  the  calcareous  soils 
of  Porto  Rico  suffers  from  chlorosis.  Analysis  shows  that  the  ash  of  these  chlor- 
otic leaves  has  less  iron  then  normal  leaves. 

Floyd^^  describes  two  types  of  injury  to  grape-fruit  seedlings  from  the  presence 
of  ground  limestone  in  the  soil.  In  addition  to  frenching  which  has  been  dis- 
cussed, chlorosis  occurs.  This  type  of  injury  may  be  attributed  to  iron  deficiency 
and  is  probably  quite  distinct  from  frenching,  since  no  case  of  the  latter  was 
observed  to  develop  into  complete  chlorosis.  The  larger  the  amount  of  limestone 
in  the  soil  the  greater  was  the  injury  observed. 

The  unavailability  of  iron  in  calcareous  soils  is  probably  attributable 
to  the  alkaline  reaction  produced  by  an  excess  of  calcium  salts  in  solution. 
Colloidal  iron  hydroxide  is  formed  in  alkaline  solutions  and  is  for  the 
most  part  unavailable  to  plants.  Similar  conditions  prevailing  in  man- 
ganiferous  soils  confirm  the  idea  that  the  basic  reaction  of  the  soil  solu- 


PLANT  NUTRIENTS  AND  THEIR  ABSORPTION  117 

tion,  rather  than  the  presence  of  specific  calcium  or  manganese  compounds, 
is  responsible  for  the  formation  of  iron  hydroxide. 

Pineapples  grown  in  Hawaii  on  the  black  manganese  soils  of  the  island  of 
Oahu  suffer  from  chlorosis.  This  condition  is  recognized  by  yellowing  of  the 
leaves,  stunted  red  or  pink  fruits,  many  of  which  crack  open  and  decay  and 
other  toxic  effects.  ^^^  Other  crops  grown  on  these  manganese  soils  suffer 
similarly,  especially  corn,  pigeon  peas,  cowpeas  and  rice.  On  the  other  hand, 
sugar  cane  is  less  sensitive  and  certain  weeds  such  as  the  sow  thistle,  Waltheria 
americana  and  Crotalaria  sp.,  show  no  effects  from  manganese. ^"^  The  difference 
between  these  two  types  of  plants  was  revealed  by  ash  analyses.  Those  to 
which  the  soil  is  toxic  have  less  iron  in  their  ash  when  grown  on  manganiferous 
soils  than  when  grown  on  ordinarj^  soils.  The  ash  of  the  weeds  growing  wild  on 
the  manganese  soils  without  apparent  ill  effects  showed  no  decrease  in  iron,  con- 
taining even  more  than  when  grown  on  other  soils.  ^'^ 

The  other  elements  in  the  ash  showed  no  such  significant  variation,  though 
in  practically  every  instance  the  absorption  of  manganese  was  increased  on  the 
manganese  soil  and  with  it  the  absorption  of  calcium. 

The  unhealthy  growth  on  the  manganese  soil  thus  appears  to  be  due 
to  a  lack  of  available  iron.  The  plants  suffered  from  iron  starvation  in 
spite  of  the   10  to  30  per  cent,  of  iron,  oxide  in  the  manganese  soils. 

Applications  of  iron  sulphate  to  the  soil,  at  rates  varying  from  500  to 
3000  pounds  to  the  acre,  were  unsuccessful  in  preventing  chlorosis; 
but  less  than  50  pounds  of  iron  sulphate  per  acre  sprayed  on  the  leaves 
effected  a  prompt  cure.^^  This  is  of  particular  interest  for  it  shows  that 
pineapple  leaves  can  absorb  enough  iron  to  cure  chlorosis,  though  the 
roots  are  not  able  to  do  so  under  the  circumstances.  It  has  been  found 
that  the  chlorosis  of  many  coniferous  seedlings  growing  on  a  calcareous 
soil  can  be  remedied  by  spraying  with  a  1  per  cent,  solution  of  iron  sulphate 
and  this  treatment  has  become  a  regular  practice  in  certain  nurseries. ^'^ 
An  interesting  treatment  more  or  less  generally  and  successfully  used 
in  France  and  Germany  for  the  cure  of  chlorosis  in  grape  vines^*^ 
consists  in  brushing  the  cut  surfaces  of  pruned  vines  with  a  concentrated 
solution  of  ferrous  sulphate.  Filling,  with  a  soluble  iron  salt,  holes  bored 
in  chlorotic  trees  frequently  has  been  tried  in  New  Mexico  and  generally 
with  satisfactory  results.  ^^^ 

From  this  discussion  of  the  effects  of  calcium  and  manganese  on 
iron,  it  is  evident  that  fertilization  may  be  of  value,  not  only  for  adding 
plant  nutrients  to  the  soil,  but  also  under  certain  conditions,  for  rendering 
soluble  and  available  to  the  plant,  nutrients  that  though  present  are 
unavailable.  Conversely,  ill  advised  fertilization  may  change  mineral 
elements  that  are  present  from  a  soluble  to  an  insoluble  form  and  there- 
fore make  them  unavailable  to  the  plant.  Through  this  effect  liming  has 
led  to  chlorosis  of  the  pineapple  in  Porto  Rico.^^  It  would  be  of  interest 
to  know  the  results  following  direct  attempts  to  change  the  reaction  of  the 


118  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

solution  of  calcareous  or  manganiferous  soils  where  chlorosis  is  produced. 
Possibly  the  application  of  acid  in  some  form  would  be  as  effective  in 
preventing  chlorosis  as  the  apphcation  of  iron  salts  to  the  leaves  or  cut 
surfaces. 

Acid  Tolerance  of  Certain  Crops. — Most  deciduous  orchard  fruits  are 
acid  tolerant  to  a  considerable  degree.  The  strawberry  has  been  shown 
to  prefer  an  acid  soil-"^  and  the  blueberry^^  demands  a  soil  markedly 
acid  in  reaction.  In  the  practically  neutral  reaction  of  a  good  garden 
loam  it  fails  to  thrive  or  even  dies  out.  The  superior  development 
of  wild  raspberries,  blackberries,  dewberries  and  haws  in  soils  that  are 
at  least  slightly  acid  suggests  that  their  cultivated  relatives  may  be 
at  home  in  similar  soil  conditions.  That  deciduous  fruits  are  not  alone 
in  their  tolerance  or  preference  for  soil  acidity  is  indicated  by  the  behavior 
of  citrus  trees  in  acid  soils. 

CoIIison"  in  reporting  the  results  of  a  series  of  fertilizer  experiments  in  Florida 
says:  "So  far  as  could  be  noted  an  acid  soil  has  no  injurious  effect  on  the  growth 
of  the  orange  tree.  On  some  of  the  most  acid  plots  in  the  grove  the  trees  are 
vigorous  and  have  made  very  good  growth,  ranking  well  up  among  the  best  plots 
in  the  grove." 

Furthermore,  practically  all  of  the  best  orchard  cover  crops  are  dis- 
tinctly acid  tolerant.  The  following  commonly  used  cover  crops  belong 
in  this  class;  cowpeas,  soy  beans,  hairy  vetch,  crimson  clover,  rye,  oats, 
millet,  buckwheat  and  turnip. ^^ 

Since  deciduous  fruit  plants  are  predominantly  acid  tolerant,  they 
should  not  be  exposed  to  a  markedly  alkaline  reaction  of  the  soil.  Ammo- 
nia in  considerable  amount  depresses  root  growth  and  eventually  kills 
the  roots,  because  of  its  effect  on  the  soil  reaction.  Injuries  resulting 
from  an  excess  of  "alkali,"  as  the  term  is  generally  used  in  the  arid  and 
semiarid  sect  ons,  are  due  not  to  any  effect  these  salts  may  have  on 
the  reaction  of  the  soil,  but  rather  to  the  excessive  concentration  of 
the  potassium  and  sodium  salts  that  are  present.  The  difference  between 
the  toxic  symptoms  attending  an  alkaline  or  basic  soil  reaction  and  those 
attending  impregnation  with  "alkali"  is  well  marked.  A  soil  solution 
having  an  alkaline  reaction  affects  the  roots  before  the  shoots;  the  toxic 
effects  of  a  soil  solution  which  is  too  concentrated  are  evident  first  in  the 
shoots. 

Concentration:  Soil  "Alkali." — As  just  pointed  out,  the  term  "soil 
alkali"  does  not  refer  to  the  soil  reaction,  but  to  an  excessive  concentra- 
tion of  certain  salts.  The  carbonates,  chlorides  and  sulfates  of  sodium 
and  potassium  are  concerned  chiefly,  though  occasionally  other  salts 
accumulate  in  such  amounts  as  to  be  injurious. 

Tolerance  of  Different  Fruits. — The  degree  of  tolerance  of  various  fruit 
crops  to  salts  of  different  kinds  is  indicated  by  data  presented  in  Table  13. 


PLANT  NUTRIENTS  AND  THEIR  ABSORPTION 


119 


Table  13. — Highest  Amount  of  Alkali  in  Which  Fruit  Trees  Were  Found 

Unaffected 

{After  Lo  ughridge^'^^) 

(Pounds  per  acre  in  4  feet  depth) 


Sulphates 

Carbonates 

Chlor 

id 

Total 

alkali 

(Glauber  salt) 

(Sal  soda) 

(Common 

salt) 

Grapes. . . 

40,800 

Grapes 7 ,  550 

Grapes .... 

9,640 

Grapes.. 

.   45,760 

Olives .  .  . 

30,640 

Oranges. ...   3,840 

Olives 

6,640 

Olives . . . 

.   40,160 

Figs 

24,480 

Olives 2,880 

Oranges .  .  . 

3,360 

Almonds. 

.   26,400 

Almonds . 

22 , 720 

Pears 1,760 

Almonds. .  . 

2,400 

Figs 

.    26,400 

Oranges. . 

18,600 

Almonds....    1,440 

Mulberry .  . 

2,240 

Oranges . 

.   21,740 

Pears. .. . 

17,800 

Prunes 1 ,  360 

Pears 

1,360 

Pears  — 

.    20,920 

Apples. . . 

14,240 

Figs 1,120 

Apples 

1,240 

Apples. . . 

.    16,120 

Peaches. . 

9,600 

Peaches 680 

Prunes .... 

1,200 

Prunes .  . 

.    11,800 

Prunes. .  . 

9,240 

Apples 640 

Peaches 

1,000 

Peaches . 

.    11,280 

Apricots. 

8,640 

Apricots 480 

Apricots. . . 

960 

Apricots . 

.    10,080 

Lemons. . 

4,480 

Lemons 480 

Lemons. . .  . 

800 

Lemons. . 

.      5 , 750 

Mulberry 

3.360 

Mulberry...        160 

Figs 

800 

Mulberry 

.     5,740 

Loughridge^^^  makes  the  following  comments  on  these  data:  "The  amount 
tolerated  depends  largely  upon  the  distribution  of  the  several  salts  in  the  vertical 
soil  column,  the  injury  being  most  severe  in  the  surface  foot,  where  under  the 
influence  of  the  unfortunate  practice  of  surface  irrigation  the  feeding  rootlets 
are  usually  found.  It  is  therefore  important  that  in  alkali  regions  such  methods 
of  culture  and  irrigation  should  be  followed  as  to  encourage  deep  rooting  on  the 
part  of  crops. 

"The  amount  tolerated  varies  with  the  variety  of  the  same  plant,  as  shown 
in  the  grape."  For  instance,  Flame  Tokay  is  reported  as  "not  growing"  with  a 
total  of  24,320  pounds  of  alkali^in  the  surface  4  feet  per  acre  while  Trousseau  is 
reported  as  thrifty  in  the  presence  of  31,360  pounds,  though  the  sal  soda  content 
of  the  Flame  Tokay  soil  was  somewhat  higher  but  still  well  within  the  general 
tolerance  limit  of  the  grape  for  this  salt. 

"The  amount  of  alkali  tolerated  by  the  various  cultures  varies  with  the 
nature  of  the  soil.  It  is  lowest  in  heavy  clay  soils  and  fine-grained  soils,  in 
which  the  downward  movement  of  plant  roots  is  restricted;  and  highest  in  loam 
and  sandy  soils,  in  which  the  roots  have  freedom  of  penetration." 

Injuries  jrom  Excessive  Fertilization. — It  is  evident  that  continued 
application  of  fertilizer  such  as  sodium  nitrate  may  produce  concentra- 
tions that  are  harmful. 

In  discussing  experiments  with  citrus  trees  Kelly  and  Thomas^"^  state: 
"While  the  growth  of  the  trees  was  notably  stimulated  by  sodium  nitrate  during 
the  first  few  years  of  the  experiment,  and  healthy,  normal  appearing  trees  were 
produced,  since  that  time  excessive  mottle  leaf  has  appeared  on  every  tree  in 
this  plot.  The  mottling  here  became  so  severe  during  the  past  2  or  3  years  as 
to  render  the  trees  wholly  unprofitable.  No  marketable  fruit  whatever  is  now 
produced  by  these  trees." 


120  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Table  14  presents  data  showing  the  toxic  limits  of  citrus  seedlings 
for  various  nitrate  salts  and  for  ammonium  sulphate  and  the  toxic  limits 
for  these  salts  in  the  presence  of  lime.  Their  lesson  in  connection  with 
the  use  of  commerical  fertilizers  in  the  orchard  is  well  summarized  in  the 
words  of  Breazeale;^^ 

"  It  will  be  seen  that  marked  differences  occur  in  the  toxic  limits  of  the  various 
salts,  sodium  nitrate  being  five  times  as  toxic  as  calcium  nitrate.  The  toxic 
limits  for  this  group  of  salts  are  so  high  that  the  matter  may  appear  to  be  of  no 
practical  import.  But  a  simple  calculation  will  show  that  the  surface  feeding 
roots  of  citrus  trees  are  at  times  subjected  to  fertilizer  concentrations  in  field 
practice  so  great  as  to  approach  toxic  conditions.  Application  of  2  to  3  pounds  of 
nitrate  of  soda  per  tree,  or  200  to  300  pounds  per  acre,  which  is  not  an  unusual 
practice  for  some  citrus  growers,  would  correspond  approximately  to  a  concen- 
tration of  70  to  100  parts  per  million  in  the  soil  of  the  surface  foot.  The  fertilizer, 
moreover,  is  ordinarily  applied  to  the  open  ground  between  the  tree  rows — that  is 
not  more  than  one-half  the  total  soil  area.  If  the  moisture  content  of  the  soil 
were  reduced  to  10  per  cent,  of  the  weight  of  the  soil,  the  concentration  of  the 
sodium  nitrate  in  the  soil  solution  would  range  from  1,400  to  2,000  parts  per 
million — that  is,  it  would  approach  the  toxic  limit.  The  surface  crusts  in  citrus 
groves  are  often  highly  toxic  to  citrus  seedlings." 

Table  14. — Toxic  Li.mits  of  Nitrates  and  Ammonium  Sulphate  p^or  Citrus 

Seedlings^* 

Toxic  Limit 
Salt  Parts  per  Million 

Sodium  nitrate 1 ,  800 

Potassium  nitrate 3 ,  500 

Calcium  nitrate 10,000 

Ammonium  sulphate 1 ,  000 

Sodium  nitrate  and  calcium  carbonate  (solid  phase) 6,000 

Ammonium  sulphate  and  calcium  carbonate* (solid  phase) 2,000 

Some  Effects  of  Soil  Alkali. — The  effects  of  excessive  concentration 
produced  by  "alkali"  on  citrus  trees  are  described  by  Kelly  and 
Thomas.  10^ 

"Different  varieties  and  species  of  citrus  trees  are  affected  differently  by 
alkali.  Lemon  trees  show  the  effects  by  a  pronounced  yellowing  of  the  margins 
and  burning  of  the  tips  of  the  leaves,  followed  by  unusually  heavy  shedding  of  the 
leaves  in  the  latter  part  of  the  winter  and  spring.  The  subsequent  new  growth 
may  appear  to  be  quite  normal  and  vigorous  for  several  months,  but  later  a  large 
portion  of  the  leaves  turn  yellow  in  irregularly  shaped  areas  around  the  margins 
and  fall  excessively.  In  the  presence  of  excessive  concentrations  of  salts,  espe- 
cially chlorides,  complete  defoliation  may  take  place.  Mottle  leaf  frequently 
occurs,  and  sometimes  chlorosis.  Both  the  quality  and  quantity  of  the  fruit  are 
impaired. 

"It  has  been  found  that  orange  trees  affected  by  alkaU  are  unusually  sus- 
ceptible to  injury  from  adverse  cUmatic  conditions.  Hot  winds  burn  the  young 
leaves  and  frosts  produce  more  serious  injury  than  with  normal  trees.     Alkali 


PLANT  NUTRIENTS  AND  THEIR  ABSORPTION  121 

injury  is  also  accentuated  by  the  lack  of  care,  such  as  improper  tillage,  the  insuffi- 
cient use  of  manure  or  other  fertilizers,  and  withholding  irrigation,  thereby  allow- 
ing the  soil  to  become  too  dry.  If  the  soil  be  allowed  to  dry  out  excessively,  the 
concentration  of  alkali  in  the  soil  moisture  may  become  harmful,  while  a  more 
abundant  supplj^  of  water  would  so  dilute  the  salts  present  as  to  reduce  the 
concentration  to  a  point  where  normal  growth  could  take  place. 

"  In  certain  localities  the  dissolved  salts  are  predominantly  chlorides,  in  others 
sulphates  and  in  still  others  bicarbonates.  A  few  wells  have  been  found  to  contain 
large  amounts  of  nitrates." 

Alkali  in  the  soil  may  also  have  a  marked  effect  on  root  distribution. 

"It  is  especially  interesting  that  the  roots  of  the  lemon  trees  have  not  pene- 
trated deeply  in  this  soil,  more  than  95  per  cent,  of  them  being  within  18  inches 
of  the  surface.  There  is  probably  some  connection  between  this  fact  and  the 
higher  concentration  of  alkali  salts  found  in  the  third  and  fourth  feet. 

"Local  areas  occur  in  a  Valencia  orange  grove  near  Garden  Grove  in  Orange 
Count}''  where  many  of  the  trees  have  been  severely  injured  by  alkali  brought  up 
as  a  result  of  a  temporarily  high  water  table  in  the  winter  and  spring  of  1916. 
The  water  table  receded  within  a  few  months  but  the  alkali  salts  remained  in  the 
soil.  A  considerable  number  of  trees  have  recently  died,  and  all  of  them  in  cer- 
tain areas  became  excessively  chlorotic,  following  the  rise  of  the  alkali." 

When  irrigation  is  practiced,  the  composition  of  the  irrigation  water  is  an 
important  factor.  Kelly  and  Thomas  found  from  their  investigations,  "a 
remarkably  close  relationship  between  the  composition  of  the  irrigation  water, 
on  the  one  hand,  and  the  accumulation  of  alkali  salts  and  the  condition  of  the 
orange  and  the  lemon  trees,  on  the  other.  In  every  case  we  have  studied,  where 
saline  irrigation  water  has  been  applied  for  a  series  of  years,  alkaline  salts  have 
accumulated  in  the  soil  and  the  citrus  trees  have  been  injured  in  consequence. 
The  rates  at  which  salts  have  actually  accumulated  vary,  however,  in  different 
soils,  depending  on  (1)  the  composition  of  the  water,  (2)  the  amounts  appUed, 
and  (3)  the  freedom  with  which  it  penetrated  into  the  subsoil. "^"^ 

The  injurious  effects  of  high  concentrations  produced  by  excessive 
amounts  of  alkaH  or  other  salts  in  the  soil  are  due  largely  to  the  inability 
of  plants  to  absorb  water  by  osmosis  from  a  solution  having  a  higher 
osmotic  concentration  than  that  of  the  plant  itself.  Hence,  the  harmful 
effects  of  alkali  are  partly  those  of  starvation  and  drought.  The  con- 
centration of  the  soil  solution  requires  attention  only  under  conditions 
where  the  salt  content  of  the  soil  is  naturally  high,  as  in  salt  marshes  and 
in  regions  near  salt  water  generally,  or  where  the  moisture  supply  is 
restricted,  as  in  arid  or  semiarid  regions.  However  summer  drought 
may  produce  temporarily  excessive  concentrations  in  any  soil  and  so 
bring  about  injury. 

Remedial  Measures. — When  a  soil  once  becomes  impregnated  with 
alkali  about  the  only  effective  treatment  is  flooding  the  land  with  irriga- 
tion water  to  dissolve  out  the  excessive  amounts  which  are  then  either 
forced  down  to  a  depth  where  they  will  do  no  harm  or  carried  away  in 
the  drainage  water.     Provision  for  thorough  drainage  is  very  important 


122  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

in  places  where  there  is  danger  from  alkah,  as  the  rise  of  the  water  table 
attending  poor  drainage  may  result  in  bringing  salts  from  lower  soil 
to  the  surface  and  thereby  increase  concentrations  in  the  upper  layers 
as  evaporation  takes  place.  Moderate,  as  opposed  to  excessive,  irrigation 
is  a  preventive  measure.  Though  there  is  not  often  a  choice  between 
two  or  more  sources  of  irrigation  water,  the  irrigation  fruit  grower  should 
remember  that  certain  water  supplies  are  more  or  less  saline  and  that 
special  precautions  must  be  taken  to  neutralize  the  injurious  effect  when 
such  water  alone  is  available.  Much  can  be  done  to  avoid  the  effects  of 
soil  alkali  through  the  choice  of  alkali-tolerant  fruit  crops  and  particularly 
the  selection  of  stocks  having  this  characteristic,  though  the  roots  of  the 
cion  may  be  susceptible.  The  importance  of  caution  in  the  use  of  fertil- 
izers, particularly  in  irrigated  sections,  has  been  mentioned. 

Finally,  it  should  be  pointed  out  that  insufficient  as  well  as  excessive 
concentrations  may  exist.  That  extremely  low  concentrations  permit 
growth  has  been  emphasized  but  it  is  the  insufficient  concentration  of 
particular  salts  that  renders  the  use  of  fertilizers  necessary. 

Soil  Toxicity. — The  chemical  composition  of  the  soil  solution  must  be 
considered  in  its  effect  on  absorption.  In  this  connection  the  presence 
of  toxic  substances  is  of  great  importance.  The  toxins  may  be  organic 
compounds  formed  by  bacterial  activity  from  dead  plant  tissue.  They 
are  not,  as  a  rule,  excreted  as  such  from  plant  roots,  though  this  occurs 
under  exceptional  conditions,  as  for  example  when  the  supply  of  oxygen 
is  deficient.  Fragments  of  dead  root  hairs,  roots  and  possibly  aerial 
portions  of  the  plant  washed  down  into  the  soil,  constitute  the  material 
acted  upon  by  microorganisms  to  produce  poisons. 

It  must  not  be  overlooked  that  bacterial  activity  may  also  produce 
compounds  beneficial  to  plant  life  in  so  far  as  the  products  of  bacterial 
action  may  serve  as  a  source  of  food,  as  has  been  pointed  out.^*^^ 

General  and  Specific  Effects. — The  general  effects  of  toxins  are  shown 
in  decreased  green  weight  and  inhibited  growth.  The  specific  morpho- 
logical effects  vary  considerably  with  different  substances,  some  producing 
more  marked  effects  on  the  roots  than  on  the  green  parts  of  the  plant. 
For  instance,  vanillin-affected  plants  show  decreased  growth  of  the  top 
and  root  growth  is  strongly  inhibited.  Dihydroxystearic  acid  affects 
the  tops  but  especially  the  roots,  the  root  tips  becoming  darkened,  their 
growth  stunted;  the  root  ends  are  enlarged  and  often  turned  upward 
like  fishhooks  and  their  oxidizing  power  is  strongly  inhibited.  Pyridine 
and  picoline  affect  the  green  parts  more  than  the  roots.  Cumarine- 
affected  plants  have  stunted  tops  and  broad  distorted  leaves;  quinone- 
affected  plants  are  tall  and  slender,  with  thin  narrow  leaves.  Guanidine 
has  apparently  no  effect  on  the  roots,  but  the  green  parts  develop  small 
bleached  spots  which  spread,  the  plant  becomes  weakened  and  the  leaves 
break  at  the  stem,  wilt  and  die.^^i''^* 


PLANT  NUTRIENTS  AND  THEIR  ABSORPTION  123 

The  manner  in  which  these  toxic  substances  check  growth  is  shown 
by  a  study  of  the  absorption  of  mineral  constituents.  Though  absorp- 
tion is  always  decreased,  the  various  toxins  have  more  or  less  specific 
effects.  Cumarin  and  salicylic  aldehyde  depress  potash  and  nitrate 
absorption  more  than  phosphate  absorption;  quinone  depresses  phosphate 
and  nitrate  more  than  potash ,  dihydroxystearic  acid  and  perhaps  vanil- 
lin, retard  phosphate  and  potash  more  than  nitrate  absorption. 

Protecting  Against  Toxins. — The  harmful  effects  of  these  toxins  may 
be  counteracted  in  numerous  ways.  Fertilizer  treatment  is  efficacious;  as 
might  be  expected,  various  salts  act  differently  in  overcoming  the  respec- 
tive effects  of  the  toxic  substances.  Phosphatic  fertilizers,  for  example, 
are  most  efficient  in  overcoming  the  effects  of  cumarin,  potassic  fertilizers 
in  overcoming  the  effects  of  quinone  and  nitrogenous  fertilizers  in  over- 
coming the  effects  of  vanillin. 

Another  way  of  ameliorating  the  effects  of  toxic  substances  in  the  soil 
is  treatment  with  absorbing  agents.  Roots  appear  able  to  oxidize 
organic  materials  in  such  a  way  that  their  toxic  properties  are  lost.  The 
large  amount  of  root  surface  which  most  plants  have  makes  this  oxidizing 
power  important  in  relation  to  the  destruction  of  toxic  substances  through 
crop  rotation. 

Schreiner,  Reed  and  Skinner^^^  found  that  toxic  solutions  lost  much  of  their 
toxicity  after  plants  had  been  grown  in  them.  They  state:  "The  vanillin' 
solution,  for  example,  was  so  reduced  in  toxicity  that  a  solution  originally  con- 
taining 500  parts  per  million  was  no  more  toxic  to  the  second  set  of  plants  than 
a  solution  of  50  parts  per  million  was  to  the  first.  It  has  been  found  that  an 
equal  number  of  wheat  plants  can  remove  in  a  similar  length  of  time  not  more 
than  30  to  50  parts  per  million  of  nitrates  from  solution  and  there  is  no  reason 
to  believe  that  toxic  substances  should  be  removed  at  a  much  more  rapid  rate." 

Breazeale^^  reports  that  peat  extract  in  dilute  concentrations  (20  parts 
per  million)  and  calcium  carbonate  protect  citrus  seedlings  against  the 
toxicity  of  distilled  water,  usually  associated  with  the  presence  of  small 
amounts  of  copper.  Sodium  carbonate  on  the  other  hand  augments  the 
toxicity  of  soluble  organic  matter. 

Thus,  "When  soluble  organic  matter  which  is  acid  in  reaction  and  stimulating 
to  citrus  seedUngs  in  concentrations  up  to  1,000  parts  per  million  or  more  is  added 
to  a  sodium  carbonate  solution  of  400  parts  per  milUon  which  in  itself  is  not 
toxic,  a  highly  toxic  solution  is  formed  which  will  kill  the  root  tips  of  citrus 
seedlings.  This  reaction  appears  to  be  of  importance  in  connection  with  the 
toxicity  of  soils  containing  small  amounts  of  sodium  carbonate."'* 

Importance  in  the  Fruit  Plantation. — To  just  what  extent  organic  soil 
toxins  are  important  in  the  fruit  plantation  is  not  known.  That  they  are 
of  greater  significance  than  is  generally  realized  there  can  be  no  question. 


124  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Most  deciduous  fruit  crops  occupy  the  same  soil  for  a  considerable  num- 
ber of  years  and  consequently  are  subject  to  the  influence  of  any  toxins 
that  arise  from  the  disintegration  of  their  own  leaves,  rootlets  or  other 
dead  tissues.  In  addition  they  are  subject  to  the  action  of  toxins  that 
may  arise  from  the  growth  or  decay  of  intercrops  or  cover  crops  that  are 
grown  between  them. 

It  has  been  shown^^  that  ordinary  crop  plants  exert  an  important 
influence  upon  those  which  follow  them  and  that  this  influence  "seems 
not  to  be  attributable,  at  least  primarily,  to  differences  in  the  amount  of 
fertilizer  nutrients  removed  by  the  crops  grown  before."  Thus  the  yield 
of  buckwheat  following  redtop,  rye,  buckwheat  and  onions  was  as  7 :  30 : 
45 :  88,  in  a  nutrient  medium  deficient  in  nitrogen  but  well  supplied  with 
other  plant  nutrients,  even  though  the  nitrogen  removal  of  the  preceding 
redtop,  rye  and  buckwheat  crops  was  as  1.00:2.72:2.42.^^  The  pre- 
sumption is  that  the  differences  in  the  yields  of  the  second  crops  were  due 
to  the  effect  of  toxins, 

Pickering ^^^  has  been  able  by  means  of  various  field  trials  and  pot 
experiments  to  eliminate  the  influence  of  one  plant  upon  another  through 
its  effect  on  moisture  and  nutrient  supply,  soil  temperature,  soil  reac- 
tion, texture,  carbon  dioxide  and  bacterial  content  and  thus  to  deter- 
mine both  quantitatively  and  qualitatively  their  mutual  influence  through 
•toxic  substances. 

He  comments  as  follows  on  the  results  of  his  investigations: 

"It  has  now  been  established  with  a  reasonable  amount  of  certainty  that  the 
deleterious  effect  of  one  growing  plant  on  another  is  a  general  phenomenon. 
By  means  chiefly  of  pot  experiments  .  .  .  the  following  plants  have  been  found 
susceptible  to  such  influence:  apples,  pears,  plums,  cherries,  six  kinds  of  forest 
trees,  mustard,  tobacco,  tomatoes,  barley,  clover,  and  two  varieties  of  grasses, 
whilst  the  plants  exercising  this  baleful  influence  have  been  apple  seedlings, 
mustard,  tobacco,  tomatoes,  two  varieties  of  clover,  and  16  varieties  of  grasses. 
In  no  case  have  negative  results  been  obtained.  The  extent  of  the  effect  varies 
very  greatly:  in  pot  experiments  the  maximum  reduction  in  growth  of  the  plants 
affected  has  been  97  per  cent.,  the  minimum  6  per  cent.,  whilst  in  field  experiments 
with  trees  the  effect  may  vary  from  a  small  quantity  up  to  that  sufficient  to 
cause  the  death  of  the  tree.  The  average  effect  in  pot  experiments  may  be 
roughly  placed  at  a  reduction  of  one-half  to  two-thirds  of  the  normal  growth 
of  the  plant,  but  no  sufficient  evidence  has  yet  been  obtained  to  justify  the  con- 
clusion that  any  particular  kinds  of  plants  are  more  susceptible  than  others,  or 
any  particular  surface  crop  is  more  toxic  than  another;  that  such  differences 
exist  is  highly  probable,  but  all  the  variations  observed  so  far  may  be  explained 
by  the  greater  or  lesser  vigour  of  the  plants  in  the  particular  experiments  in 
question.  Similarly  as  regards  the  effect  of  grass  on  fruit  trees,  though  the  extent 
of  it  varies  very  greatly,  and  in  many  soils  is  certainly  small,  we  must  hesitate 
to  attribute  this  to  any  specific  properties  of  the  soils  in  question ;  for  when  soils 
from  different  localities  (including  those  from  places  where  the  grass  effect  is 


PLANT  NUTRIENTS  AND  THEIR  ABSORPTION  125 

small)  have  been  examined  in  pot  experiments,  they  have  all  given  very  similar 
results;  and  this  appUes  equally  to  cases  where  pure  sand,  with  the  addition  of 
artificial  nutrients,  has  been  taken  as  the  medium  of  growth."'^"  Evidence 
which  will  serve  partially  to  differentiate  between  the  influence  of  a  living  plant 
and  the  disintegration  products  of  its  dying  roots  is  afforded  by  the  following: 
"...  a  quarter  of  an  acre  of  land,  over  which  some  15  apple  trees,  20  years 
of  age,  were  distributed,  was  planted  uniformly  with  Brussels  sprouts;  those 
under  the  trees  suffered  to  the  extent  of  48  per  cent,  in  their  growth;  but  there 
were  patches  in  the  ground  where  trees  had  been  growing  until  the  preceding 
winter,  when  they  had  been  cut  down,  leaving  the  roots  undisturbed  in  the  soil, 
and  in  these  patches  the  sprouts  did  better  than  elsewhere  to  the  extent  of  12 
per  cent.  In  other  parts  of  the  ground  canvas  screens  had  been  erected,  at  a 
height  of  6  feet  above  the  surface,  to  simulate,  and  even  exaggerate,  the  shading 
of  the  trees,  and  under  these  the  sprouts  gave  exactly  the  same  values  as  on  the 
unshaded  ground.  Thus,  the  trees  themselves  materially  injured  the  crop, 
though  the  soil  under  the  trees  was  more  fertile  than  elsewhere,  and  though 
the  shading  was  inoperative."'^" 

The  degree  of  susceptibility  of  the  apple  tree  to  the  toxic  influence  of 
some  other  plant  is  indicated  by  Pickering's^^''  statement  that  the  color  of 
the  fruit  may  be  materially  affected  "in  cases  of  trees  weighing  about  2 
hundredweight  when  only  3  to  6  ounces  of  their  roots  extended  into 
grassed  ground." 

Though,  as  stated  already,  data  are  not  available  for  the  accurate 
•estimation  of  the  importance  of  organic  toxins  in  fruit  production,  the 
limited  data  are  very  suggestive. 

In  commenting  upon  the  investigations  that  have  just  been  cited  and  on 
others  of  a  similar  character  Alderman''  remarks:  "Do  they  not  at  least  open  to 
some  question  many  of  our  preconceived  ideas  bearing  upon  plant  growth  and 
plant  nutrition?  .  .  .  Do  they  not  raise  a  question  as  to  the  arrangement  of 
many  crop  rotations  {e.g.,  of  cover  crops  or  other  intercultures)  which  were 
originally  worked  out  with  the  economic  convenience  of  the  grower  in  view  rather 
than  the  growth  reactions  of  the  plants  under  consideration?  .  .  .  If  it  is  true 
in  Rhode  Island  that  onions  will  yield  412  bushels  per  acre  following  redtop  and 
only  13  bushels  following  cabbages,  it  is  probably  true  elsewhere  and  the  place 
of  the  onion  in  the  cropping  system  of  the  truck  grower  deserves  the  most  serious 
study.  If  grass  affords  direct  injury  to  apple  trees  growing  in  shallow  soils 
underlaid  with  an  impervious  stratum  of  subsoil,  it  is  probably  as  offensive  in 
North  America  as  in  England.  The  writer  and  others  interested  in  plant  nutri- 
tion have  repeatedly  pointed  out  the  difference  in  reaction  to  fertilizers  between 
orchards  in  sod  and  those  under  cultivation.  It  has  been  generally  believed  that 
this  difference  was  due  to  soil  exhaustion  of  important  plant  food  material  or  to 
an  influence  on  moisture  supply  but  the  work  of  Pickering  is  a  direct  challenge 
to  such  a  belief.  Perhaps  it  is  not  important  to  the  grower  of  fruit  to  know 
whether  an  application  of  nitrate  of  soda  to  a  sod  orchard  is  beneficial  because 
it  supplies  some  element  of  plant  food  material  heretofore  lacking  or  because  it 


126 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


hastens  the  change  of  toxic  substances  to  harmless  or  beneficial  materials,  but  it 
is  extremely  important  to  the  investigator  for  it  strikes  back  to  a  fundamental 
problem  in  plant  nutrition." 

The  whole  question  of  the  interrelationship  of  plants  in  the  orchard 
still  needs  thorough  investigation. 

Antagonism. — Beside  organic  poisons,  certain  inorganic  salts  may 
have  toxic  effects;  for  example,  magnesium  compounds  may  become 
injurious  to  the  higher  plants.  The  toxic  action  of  magnesium  is  modified, 
however,  by  calcium  because  of  the  antagonism  between  these  two  ele- 
ments. Salts  of  either  calcium  or  magnesium  by  themselves  tend  to 
increase  the  permeability  of  protoplasm  more  than  a  mixture  of  calcium 
and  magnesium  salts  in  proper  proportion.  Therefore,  the  action  of 
calcium  in  offsetting  the  toxic  effect  of  the  magnesium  probably  is  due 
to  diminished  magnesium  absorption  when  both  elements  are  present  in 
suitable  proportion.  Antagonism  occurs  also  between  calcium  and 
potassium  and  many  other  salts. 

Aeration. — In  the  absence  of  aeration  roots  are  unable  to  function  prop- 
erly and  toxic  substances  are  secreted.  Moreover  poor  aeration  favors 
the  formation  of  toxins  by  bacteria  and  in  the  absence  of  an  adequate 
supply  of  oxygen,  numerous  soil  bacteria  reduce  nitrates,  utilize  the  oxy- 
gen and  leave  gaseous  nitrogen  which  is  not  available  to  the  higher  plants. 

The  physical  character  of  the  soil  has  an  important  effect  on  aeration; 
stiff,  retentive  clays,  for  example,  do  not  drain  as  well  as  sandy  soils; 
consequently  they  are  usually  not  so  well  aerated.  The  application  of 
Hme  or  organic  fertilizers  to  such  clays  may  render  them  mellow,  better 
drained  and  more  readily  cultivated. 

Selective  Absorption.— Within  certain  limits,  plants  are  able  to 
absorb  larger  amounts  of  one  mineral  constituent  at  their  disposal  than 
of  another  and  in  this  way  to  exert  a  selective  action.  This  is  strikingly 
shown  by  Table  15,  which  compares  the  percentage  composition  of  the 
ash  of  duckweed  with  the  water  in  which  it  grew. 


Table  15. 


-Analyses  of  Ash  of  Duckweed  and  of  the  Mineral  Matter  Con- 
tained IN  THE  Water  in  Which  It  Grew'"* 


K2O 

Na^O 

CaO 

MgO 

FeaOs 

P2O5 

SO  3 

Si02 

CI 

Duckweed 

Water 

18.29 
5.15 

4.05 
7.60 

21.86 
45.55 

6.60 
16.00 

9.57 
0.94 

11.35      7.91 
3.42    10.79 

16.05 
'4.23 

5.55 
7.99 

This  selective  abihty  of  the  plant  may  be  explained  by  greater  action 
on  certain  constituents  which  are  thereby  rendered  osmotically  inactive 
within  the  plant.  This  leads  to  further  absorption  of  these  particular 
constituents.     However,  selective  action  has  definite  limits  and  plants 


PLANT  NUTRIENTS  AND  THEIR  ABSORPTION  127 

absorb  a  certain  amount  of  any  constituent  which  is  present  in  an 
available  form  and  to  which  the  protoplasm  is  permeable.  Thus,  salt 
marsh  plants  contain  relatively  large  amounts  of  sodium  chloride  which 
may  raise  the  osmotic  concentration  of  their  cell  sap,  but  is  of  no 
apparent  nutritive  value.  Similarly  plants  grown  in  nutrient  solutions 
absorb  whatever  salts  are  present  in  solution,  though  the  rate  is  greatest 
and  growth  best  when  the  nutrient  substances  are  available  to  the  plant 
in  a  ratio  corresponding  to  that  in  which  they  are  utilized. 

Investigations  by  Schreiner  and  Skinner^'^^  bearing  on  this  subject  are  very 
suggestive:  "In  this  study  the  growth  relationships  and  concentration  differ- 
ences were  observed  between  sohition  cultures  in  which  the  phosphate,  nitrate 
and  potash  varied  from  single  constituents  to  mixtures  of  two  and  three  in  all 
possible  ratios  in  10  per  cent,  stages.  The  better  growth  occurred  when  all  these 
nutrient  elements  were  present  and  was  best  in  those  mixtures  which  contained 
between  10  and  30  per  cent,  phosphate;  between  30  and  60  per  cent,  nitrate; 
and  between  30  and  60  per  cent,  potash.  The  growth  in  the  solutions  containing 
all  three  constituents  was  much  greater  than  in  the  solutions  containing  two 
constituents,  the  solutions  containing  the  single  constituents  giving  the  least 
growth.  The  concentration  differences  noticed  in  the  solutions  were  also  very 
striking,  the  greater  reduction  in  concentration  occurring  where  the  greatest 
growth  occurred.  The  change  in  the  ratios  of  the  solutions  and  the  ratios  of 
the  materials  that  were  removed  from  the  solutions  showed  that  where  greatest 
growth  occurred,  as  above  outlined,  the  solutions  suffered  the  least  change 
in  ratio,  although  the  greatest  change  in  concentration  occurred.  The  more  the 
ratios  in  these  solutions  differed  from  the  ratios  in  which  the  greatest  growth 
occurred,  the  more  were  the  solutions  altered  in  the  course  of  the  experiment, 
the  tendency  in  all  cases  seeming  to  be  for  the  plant  to  remove  from  any  and  all 
of  these  solutions  the  ratio  which  normally  existed  where  greatest  growth  occurred, 
but  was  hindered  in  doing  so  by  the  unbalanced  condition  of  the  solution.  The 
results  show  that  the  higher  the  amount  of  any  one  constituent  present  in  the 
solution,  the  more  does  the  culture  growing  in  that  solution  take  up  of  this 
constituent,  although  it  does  not  seem  able  to  use  this  additional  amount 
economically." 

Similarly  surpluses  of  lime  in  plants  are  not  uncommon.  ^^4  ^  p^j-t 
of  the  lime  may  be  precipitated  as  calcium  oxalate,  or  in  some  plants 
as  calcium  carbonate,  of  which  cystoliths  are  largely  composed. 

Transpiration. — The  ash  content  of  plants  varies  considerably  under 
different  conditions  of  soil  water,  available  salt  supply  and  temperature. 
Data  have  been  reported^"^  indicating  that  increased  transpiration 
does  not  increase  the  ash  absorption  of  plants  growing  in  soil.  For 
this  reason  conclusions  from  experiments  involving  nutrient  solutions 
should  be  applied  to  field  conditions  with  extreme  caution.  Transpira- 
tion and  the  absorption  of  nutrient  salts  are  largely  independent  of  each 
other. 


128  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Schreiner  and  Skinner""'''  discuss  this  subject  as  follows:  "Many  writers  in 
agricultural  literature  seem  to  be  under  the  impression  that  the  only  way  that  a 
plant  can  get  the  nutrients  from  a  solution  is  to  use  all  the  water  it  can  in  building 
tissue  and  to  lose  the  remainder  by  transpiration,  so  as  to  obtain  the  necessary 
nutrients  dissolved  in  the  soil  water  or  nutrient  solution.  In  other  words,  that 
the  plant  maintains  a  current  of  water  entering  at  the  root  as  the  nutrient 
solution  and  leaving  the  plant  as  pure  water  at  the  leaf  surfaces,  that  is,  by 
transpiration  or  evaporation.  From  their  arguments  it  follows  that  if  a  half 
strength  solution  is  presented  to  the  plant  it  will  have  to  take  up  and  transpire 
twice  as  much  water  to  obtain  the  same  nutrients.  In  other  words,  the  plant 
is  supposed  to  absorb  the  mineral  constituents  in  the  same  concentration  as  the 
solution  in  which  the  roots  bathe.  This  is,  however,  not  in  accordance  with 
the  facts.  The  plant  has  greater  difficulty  in  obtaining  the  mineral  elements  from 
the  weaker  solution,  but  it  does  not  accomplish  this  by  expending  the  extra  energy 
involved  in  transpiring  double  the  amount  of  water. 

"For  instance,  the  loss  of  water  from  a  250-cubic  centimeter  [nutrient] 
solution  during  this  3-day  period  is  only  about  10  per  cent.,  whereas  the  analysis 
of  the  solution  after  supplying  this  water  showed  the  mineral  nutrients  to  be 
reduced  from  80  to  as  low  as  23.8  parts  per  million,  or  a  decrease  of  70  per  cent. 
It  is  obvious  that  the  plants  have  taken  the  nutrients  faster  than  the  water,  and 
this  under  conditions  of  good  growth. 

"Not  only  does  the  absorbing  power  of  the  root  enable  the  plant  to  take  more 
nutrients  per  cubic  centimeter  of  water  absorbed  than  is  contained  in  the  same 
volume  of  the  soil  solution,  but  it  also  enables  the  plant  to  obtain  a  different 
ratio  of  the  mineral  nutrients  for  its  use  than  exist  in  the  nutrient  solution. 

"These  facts  are  extremely  important,  as  they  show  that  the  absorbing  power 
of  the  plant  is  not  regulated  by  the  amount  of  transpiration,  but  rather  by  the 
life  processes  within  the  plant  and  the  requirements  of  these  life  processes." 

THE  NUTRIENT  REQUIREMENTS  OF  CROP  AND  FRUIT  PLANTS 

Typical  crop  plants  and  typical  deciduous  fruits  make  distinctly 
different  demands  upon  the  soil.  For  most  crops  the  soil  should  not  be 
acid  and  the  nitrogen  requirement  is  relatively  low.  For  most  fruit 
trees,  soil  acidity,  unless  very  high,  is  not  a  factor  of  concern  and  the 
demands  for  nitrogen  are  great.  It  is  suggested  that  this  more  or  less 
characteristic  difference  which  requires  agronomists  and  horticulturists 
to  adopt  correspondingly  different  attitudes  on  the  problem  of  soil 
productivity  is  connected  with  the  different  ecological  habits  of  these 
plants,  together  with  the  type  of  crop  desired.  Cereal  crops  in  particular 
are  adapted  to  an  early  stage  in  ecological  succession  which  has  not 
proceeded  beyond  an  association  where  grasses  are  dominant.  Humus 
has  not  yet  collected  in  great  amount;  hence,  crops  flourish  in  soils  of  low 
acidity  and  require  relatively  little  nitrogen  (though  they  may  do  equally 
well  or  better  in  soils  abundantly  supphed  with  it).  Fruit  trees  belong  to 
a  much  later  stage  in  an  ecological  succession  which  has  reached  an 
association  of  forest  trees  and  in  which  the  character  of  the  soil  has 


PLANT  NUTRIENTS  AND  THEIR  ABSORPTION  129 

been  affected  by  previous  plant  associations  that  have  grown  on  it. 
Humus  is  therefore  more  abundant  and  the  plants  are  adapted  to  soils 
of  relatively  high  acidity  and  great  nitrogen  content.  Hence,  lime 
is  most  useful  for  crops  and  nitrogen  the  fertilizer  most  often  required  by 
fruit  trees.  It  is  more  profitable  to  grow  cereal  crops  on  the  great  plains, 
prairies,  savannahs  and  pampas  while  fruit  trees  thrive  best  in  the  regions 
of  coniferous  and  deciduous  forests. 

Summary. — The  various  mineral  elements  and  nitrogen  are  absorbed 
by  the  plant  from  the  soil  solution.  These  mineral  elements,  except  a 
portion  of  the  sulphur,  may  be  recovered  in  the  ash  of  the  plant.  In 
addition  to  the  necessary  mineral  elements,  the  ash  generally  includes 
small  quantities  of  a  number  of  non-essential  elements  occurring  in  the 
soil  solution.  The  ash  content  of  plants  varies  with  the  kind  of  plant 
and  with  the  soil  upon  which  it  is  grown.  The  ash  content  of  different 
tissues  also  varies  with  the  kind  of  tissue,  its  age  and  the  season.  Nutri- 
ent elements  must  not  only  be  in  solution  but  must  be  in  an  available 
form — that  is,  combined  with  certain  other  elements  and  in  certain 
compounds.  Nitrogen  is  absorbed  mainly  as  nitrates.  The  nitrate 
supply  in  the  soil  is  subject  to  great  fluctuations,  depending  on  tem- 
perature, moisture,  aeration,  bacterial  activity,  the  supply  of  nitrogen- 
carrying  materials  from  which  nitrates  can  be  formed  and  many  other 
factors.  An  important  part  of  the  orchard  soil  fertility  question  consists 
in  maintaining  a  liberal  supply  of  nitrates  in  the  soil  during  the  growing 
season.  Most  crop  plants  prefer  a  soil  practically  neutral  in  reaction. 
Deciduous  fruits  are  distinctly  acid  tolerant  and  certain  of  them  thrive 
best  in  an  acid  soil.  The  best  orchard  cover  crops  are  likewise  acid 
tolerant.  The  chlorotic  conditions  frequently  found  in  strongly  cal- 
careous and  manganiferous  soils  apparently  are  due  to  iron  starvation 
incident  to  an  alkaline  reaction.  Many  organic  disintegration  products 
are  known  to  be  toxic  to  certain  crop  plants  and  there  is  evidence  that 
they  are  often  of  considerable  importance  in  determining  the  produc- 
tivity of  orchard  soils.  Some  of  the  injurious  effects  of  sod  upon  trees 
evidently  are  due  to  these  toxins  in  the  grass  land.  Excessive  concen- 
trations of  certain  salts,  particularly  of  sodium  and  potassium,  are  toxic  to 
orchard  trees  and  give  rise  to  the  so-called  "alkali"  conditions.  Treat- 
ment for  disorders  of  this  kind  may  be  both  remedial  and  preventive. 
Optimum  conditions  for  absorption  are  provided  when  the  various 
nutrient  elements  are  found  in  the  soil  solution  in  certain  rather  definite 
proportions.  Sometimes  harmful  influences  result  when  these  ratios 
do  not  obtain.  Both  transpiration  and  soil  aeration  influence  somewhat 
the  rate  of  absorption.  Within  certain  limits  plants  are  able  to  absorb 
from  the  soil  solution  the  elements  most  necessary,  taking  them  out  in 
proportions  sometimes  very  different  from  those  in  which  they  exist. 


CHAPTER  VIII 

INDIVIDUAL  ELEMENTS 

The  intake  of  nitrogen  and  mineral  constituents  in  inorganic  form 
has  been  described.  Their  incorporation  into  the  plant  is  now  considered 
with  particular  reference  to  orchard  or  fruit  plants.  In  the  study  of 
nitrogen  content  analyses  are  expressed  in  percentages  of  fresh  weight  or 
of  dry  weight  or  in  the  absolute  amounts  present  in  a  certain  tissue  such 
as  100  leaves;  ash  analyses  are  given  in  percentages  of  fresh  weight  or 
of  dry  weight,  in  percentages  of  total  ash  or  in  absolute  amounts. 
Careful  distinction  should  be  made  between  determinations  expressed 
in  these  different  terms  since  they  are  not  comparable.  For  example, 
during  the  development  of  a  tissue — say  the  leaf — some  ash  constituent 
may  decrease  in  terms  Of  percentage  of  total  ash,  remain  constant  in 
percentage  of  dry  weight  and  increase  in  absolute  amount.  Absolute 
amounts  are  particularly  valuable  data  and  show  the  actual  changes 
in  the  amount  of  substance  present.  Percentages  of  dry  weight  will 
indicate  the  same  changes  provided  there  is  no  increase  or  decrease 
in  the  absolute  dry  weight.  If  there  is,  then  these  changes  must  be 
taken  into  consideration.  Expression  of  percentage  in  terms  of  fresh 
weight  involves  in  addition  changes  in  the  water  content.  Percentages 
of  total  ash  show  the  relative  proportions  of  the  various  ash  constituents. 
Each  of  these  determinations  has  its  value,  but  each  expresses  different 
relations. 

NITROGEN 

Nitrogen  enters  the  roots  from  the  soil  solution  as  a  salt  of  nitric  acid,, 
such  as  potassium  or  sodium  nitrate,  or  sometimes  as  ammonia.  The 
supply  of  nitrates  in  the  soil  varies  with  temperature  and  moisture, 
usually  being  greatest  in  late  spring  and  early  autumn,  but  persisting 
throughout  the  summer. 

Synthesis  of  Organic  Nitrogenous  Compounds. — Most  of  the  inorganic 
nitrogen  absorbed  is  carried  up  the  trunk  and  branches  to  the  leaves 
where  it  is  elaborated  into  amino-acids  and  other  nitrogenous  organic 
compounds.  The  elaboration  of  nitrates  to  amino-acids  takes  place  for 
the  most  part  in  the  chloroplasts  of  the  leaf  mesophyll  cells.  Light  has 
been  shown^^^  to  increase  nitrogen  assimilation,  blue-violet  and  ultra- 
violet light  being  particularly  effective.  Light  from  the  blue  end  of  the 
solar  spectrum  is  relatively  stronger  in  cloudy  weather;  light  from  the 
other  end  of  the  spectrum  which  is  the  more  important  for  the  photo- 

130 


INDIVIDUAL  ELEMENTS  131 

synthetic  process,  predominates  in  direct  sunlight.  According  to  one 
investigator^^^  the  influence  of  Hght  in  favoring  protein  formation  and 
the  elaboration  of  inorganic  to  organic  nitrogenous  compounds  becomes 
more  pronounced  as  the  stage  of  development  advances.  Nitrogen 
elaboration  can  take  place  in  the  absence  of  chlorophyll  and  light,  in 
which  case  presumably  carbohydrates  are  used.-"^  The  amino-acids 
which  are  the  first  products  of  elaboration  are  either  used  directly  in 
the  leaf  or  are  conducted  through  the  phloem  to  all  parts  of  the  plant 
where  they  are  used  in  the  building  up  of  every  nitrogen-containing 
organic  compound  found  in  plants  as  well  as  of  certain  nitrogen-free 
organic  substances  (essential  oils,  resins  and  polyterpenes).  The  amino- 
acids  are  combined  to  form  the  proteins  which  occur  in  all  protoplasm. 
Other  nitrogenous  organic  compounds  are  the  purines  and  pyrimidines 
which  enter  into  the  composition  of  nucleic  acids,  nucleins  and  nucleo- 
proteins,  substances  characteristic  of  the  cell  nucleus.  Lecithins  and 
chlorophyll  contain  nitrogen.  Nitrogen-containing  compounds  which 
are  not  of  universal  occurrence  are  the  alkaloids,  ptomaines,  amines, 
cyanogenetic  glucosides  and  indican  (natural  indigo  blue). 

Translocation  and  Use  of  Elaborated  Nitrogenous  Compounds. — The 
elaboration  of  nitrates  to  amino-acids  beginning  at  the  time  the  leaves 
are  well  developed,  proceeds  as  long  as  they  remain  green,  reaching  a 
maximum  when  temperature,  light  and  soil  supply  conditions  are  at  an 
optimum.  The  elaborated  nitrogen-containing  compounds  are  con- 
stantly passing  out  of  the  leaves  throughout  the  season  of  elaboration  as 
fast  as  they  are  made.  They  are  used  for  new  tissue  development,  for 
shoot  growth,  new  leaves,  increments  to  branches,  trunks  and  roots,  new 
roots  and  especially  for  fruit  and  seed  development.  A  considerable  part 
of  the  remainder  is  stored  in  the  phloem.  Storage  is  particularly  rapid 
in  the  fall  when  growth  has  ceased  and  before  the  leaves  are  separated 
from  the  plant  by  abscission  layers. 

New  tissue  growth  in  early  spring  is  at  the  expense  of  stored  foods, 
including  stored  nitrogen.  This  reserve  supplies  the  developing  shoots, 
leaves,  flowers,  rootlets,  much  of  the  new  tissue  in  trunk,  branches  and 
roots  and  the  fruit  in  its  initial  stages.  Hence  for  good  spring  growth  of 
tissues,  especially  shoots,  leaves  and  spurs,  abundant  nitrogen  storage  the 
previous  season  is  a  prime  requisite.  This,  in  turn,  depends  on  a 
good  supply  of  available  nitrogen  in  the  soil  between  June  1  and  Sept.  15 
or  Oct.  15,  a  supply  more  than  sufficient  for  fruit  and  tissue  development. 
Summer  defoliation  or  a  diseased  condition  of  the  leaves  evidently  checks 
growth  the  following  year  by  cutting  down  the  supply  of  stored  and  elabo- 
rated nitrogen. 

Attention  should  be  called  to  the  apparent  usefulness  of  unelaborated 
nitrogen  to  the  apple  and  pear  tree  and  probably  to  other  fruits,  through 
enabhng  them  to  set  a  larger  crop.     It  is  a  common  experience  to  secure 


132 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


a  good  set  of  fruit  when  liberal  applications  of  some  readily  available 
nitrogen-carrying  fertilizer,  such  as  nitrate  of  soda,  are  made  to  weak 
trees  just  before  blossoming,  though  without  such  applications  these 
same  trees  would  bloom  heavily  but  set  little  or  no  fruit.  This  response 
by  the  tree  is  obtained  within  2  or  3  weeks  after  application  of  the  fer- 
tilizer and  at  a  season  when  there  is  practically  no  leaf  area  to  build  up 
elaborated  foods.  It  would  seem,  therefore,  that  the  synthesis  of  organic 
nitrogenous  compounds  can  take  place  in  tissues  other  than  the  leaves. 

Seasonal  Distribution  of  Nitrogen. — A  study  of  the  seasonal  variation 
in  nitrogen  content  of  different  parts  of  the  plant  gives  a  perspective  of 
the  processes  of  nitrogen  elaboration,  storage  and  utilization. 


1/ 


<;}- 

— 

c3    ^ 

rO 

^ 

3 

3 

^' 

^^  ^ 

-> 

3 
—> 

< 

<   «n 

Fig.   11. — Nitrogen  content  of  plum  leaves  in  percentages  of  dry  weight.      (Plotted  from 
data  given  by  Richter.*^^) 


In  Leaves. — Since  the  leaf  is  the  principal  organ  of  nitrogen  elaboration  the 
seasonal  distribution  of  this  element  in  the  leaf  is  important.  Leaf  buds  have  a 
high  percentage  of  nitrogen;  certain  analyses  show  3.687  per  cent,  of  the  dry 
weight  in  the  cherry  and  3.779  per  cent,  in  the  plum.i^e  Fruit  buds  have  a 
slightly  higher  percentage  composition  in  nitrogen,  corresponding  analyses 
showing  3.771  per  cent,  in  the  cherry  and  4.142  per  cent,  in  the  plum.i^^ 

Table  16  shows  the  decrease  in  percentages  of  nitrogen  in  apple,  pear  and 
cherry  leaves  from  May  to  October.  ^^^  This  is  shown  even  more  clearly  by  the 
graph  in  Fig.  11.  The  accompanying  composite  table  (Table  17)  is  a  good 
illustration  of  the  steady  decrease  in  the  percentage  nitrogen  content  of  plum 
leaves.  Though  there  is  a  continuous  decline  in  the  percentage  of  nitrogen  from 
May  through  October,  there  are  two  periods  of  rapid  decrease,  one  in  May  and 
the  other  in  September.  Between  the  periods  of  rapid  decrease  the  percentage 
composition  of  the  leaf  is  fairly  constant.  The  first  period  of  decrease  is  at  the 
time  when  the  leaf  is  growing  rapidly  and  the  available  nitrogen  supply  is  limited, 
because  of  rapid  and  simultaneous  shoot,  wood  and  root  development.  The 
period  of  relatively  constant  nitrogen  content  occurs  when  nitrogen  intake  is 


INDIVIDUAL  ELEMENTS 


133 


Table    16.— Nitrogen   in  Leaves  of  Apple,  Pear  and  Cherry '^^ 
(In  percentage  of  dry  weight) 


Apple 

Pear 

Cherry 

May  9,  14 

4.152 
2.628 
2.015 
1.198 

4.087 
2.782 
2.041 

0.917 

4.867 
2  639 

Aug  29 

2  160 

Oct.  2,  15 

1 .  022 

Table    17. — Nitrogen  of  Plum  Leaves^" 
(In  percentage  of  dry  weight) 


May  18,  1908 4.917 

May  27,  1907 3.809 

June  22,  1908 2.208 

July  14,  1909 2.917 

July  31,  1909 2.816 


Aug.  21,  1909 2.402 

Aug.  29,  1908 2.398 

Sept.  6,  1909 2.413 

Sept.  30,  1908 1 .  152 

Oct.  28,  1909 1.096 


very  nearly  balanced  by  the  demands  for  new  vegetative  tissue  and  for  the  develop- 
ment of  the  fruit  and  seed.  The  second  period  of  decrease  indicates  rapid  deple- 
tion of  the  nitrogen  content  of  the  leaf,  the  withdrawal  being  much  in  excess  of 
the,  amount  supplied.  This  picture  presented  by  the  plum  is  fairly  typical  of 
other  deciduous  fruits. 

On  the  other  hand,  the  absolute  amount  of  nitrogen  in  the  leaves  does  not 
decrease  throughout  the  season.  Table  18,  showing  grams  of  nitrogen  in  100 
apple,  pear,  cherry  and  plum  leaves  from  July  to  October,  brings  this  out  clearly 
and  shows  that  the  absolute  nitrogen  content  of  leaves  does  not  decrease 
materially  until  after  September.     In  all  probability  it  is  increa.sing  until  August. 


T.\ble  18. — Grams  of  Nitrogen  in  100  Leaves^ 


Apple 


Pear 


Cherry 


Plum 


July  14 

July  31 

Aug.  18,  21.... 
Sept.  3,  4,  6.  .. 

Oct.  7 

Oct.  23,  27,  29. 
Nov.  4 


0.704 
0.734 
0.795 
0.742 


0.232 


0.401 
0.421 
0.409 
0.368 


0.121 


0.713 
0.553 
0.624 
0.593 
0.602 
0.178 


0.555 
0.477 
0.376 
0.389 


O.ISO 


A  comparison  of  the  data  showing  absokite  nitrogen  content  with  the  data 
showing  percentage  composition  of  the  dry  weight  indicates  that  in  young  leaves 
with  their  high  percentage  of  nitrogen,  growth  and  carbohydrate  formation 
proceed  at  such  a  rate  as  to  reduce  the  percentage  composition  of  nitrogen  even 
though  the  intake  of  nitrates  during  this  period  is  greater  than  the  outgo  of 
elaborated  nitrogen.     During  July  and  August  and  sometimes  later,  the  leaf 


134 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


supplies  the  branches  with  an  amount  of  elaborated  nitrogen  about  equal  to  the 
amount  of  nitrates  taken  in.  From  September  on,  however,  the  leaves  receive 
less  nitrate  in  proportion  to  the  elaborated  nitrogen  which  passes  back  into  the 
branches;  consequently  the  percentage  nitrogen  content  of  the  leaf  is  cut  in 
half  and  only  one-third  the  amount  the  leaves  once  contained  remains  in  them 
when  thej^  fall. 

In  Branches,  Trunks  and  Roots. — A  study  of  the  seasonal  variation  in  the 
content  of  various  parts  of  a  tree  shows  what  becomes  of  the  nitrogen  that  passes 
out  of  the  leaf.  Table  19  shows  the  distribution  of  nitrogen  in  a  7-year  old  apple 
tree  at  different  seasons.  Nitrogen  content  is  expressed  in  percentages  of  dry 
weight. 


Table    19. — Seasonal   Changes   in  the   Nitrogen   Content  of   a  7-year  Old 

Apple  Tree^^ 

(Percentages  of  dry  weight) 


Dormant, 
Dec.  3 


Buds 
swelling, 
Apr. 


20 


In  bloom. 
May  18 


Active 

growth 

over, 

July  12 


Leaves 
falling, 
Oct.  12 


Summer's  growth.  . . 
1-year  old  branches . 
2-year  old  branches. 
3-year  old  branches. 
4-year  old  branches. 
5-year  old  branches. 

Trunk 

Large  roots 

Small  roots 


0.80 
0.63 
0.42 
0.40 
0.39 
0.23 
0.41 
0.79 


1.01 
0.68 
0.62 
0.41 
0.32 
0.32 
0.47 
0.78 


0.69 
0.38 
0.32 
0.29 
0.28 
0.27 
0.46 
0.70 


0.64 
0.40 
0.32 
0.27 
0.24 
0.23 
0.22 
0.28 
0.48 


0.61 
0.57 
0.50 
0.37 
0.30 
0.25 
0.24 
0.31 
0.77 


These  figures  bring  out  two  important  points — first,  that  the  younger  the 
tissue  the  greater  is  its  nitrogen  content  and  second,  that  practically  all  tissues 
have  a  minimum  when  active  growth  has  ceased  and  a  maximum  at  the  time  of 
bud  swelling.  The  increase  in  all  tissues,  except  leaves,  during  the  fall  indicates 
nitrogen  storage.  The  nitrogen  that  is  stored  over  the  winter  evidently  comes 
from  the  leaves. 

Reference  to  the  last  table  shows  that  in  two  places  only  is  there  a  decrease 
in  the  percentage  of  nitrogen  before  bud  swelling,  namely,  in  the  smaller  roots 
and  in  the  5-year  old  branches.  The  decrease  in  the  roots  probably  is  due  to 
their  beginning  to  function  and  to  renew  growth  earher  in  the  spring  than  do  the 


In  Spurs. — The  seasonal  changes  in  the  nitrogen  content  of  bearing,  non- 
bearing  and  barren  spurs  from  mature  apple  trees  is  shown  in  Fig.  12. 
The  variations  in  non-bearing  spurs,  or  more  accurately  productive  spurs  in  the 
off  year,  are  similar  to  those  in  the  roots,  trunks  and  branches  with  a  maximum 
in  March  at  the  time  of  bud  swelling  and  a  minimum  at  the  end  of  June  when 
growth  is  over.^°"    Barren  spurs  have  a  lower  nitrogen  content  throughout  the 


INDIVIDUAL  ELEMENTS 


135 


year  and  there  is  little  evidence  of  accumulation  in  the  fall;  this  may  be  associated 
with  the  absence  of  fruit  bud  differentiation  in  these  spurs. 

Bearing  spurs  are  peculiar,  however,  in  that  their  nitrogen  content  increases 
after  the  buds  have  broken,  though  in  all  other  tissues  of  spur-bearing  trees  it 
decreases  when  the  plant  is  in  bloom.  This  indicates  that  though  the  vegetative 
tissues  use  locally  stored  nitrogen  with  the  result  that  their  nitrogen  content 
decreases,  the  blossoming  spurs  draw  on  a  general  supply  and  latet-  upon  the  new 
supply  of  the  current  season  with  the  result  that  their  nitrogen  content  is  aug- 
mented up  to  the  time  of  fruit  setting.  This  reserve  supply  is  located  probably 
in  the  phloem,  for  a  marked  decrease  in  the  nitrogen  content  of  bark  has  been 
found  in  many  plants.^"     In  Rhus  elegans  for  example  the  bark  has  been  found 


A 

\* 

/. 

r 

\ 

/ 

/ 

K 

/ 

B 

/ 

\ 

\ 

y 

/ 

A 

A 

\ 

\ 

W 

5 

^ 

N 

J 

\^ 

\ 

\ 

^^ — 
\   1 

w 

■^ 

^.^ 

^^.^ 

^ 

fe 

1.0 

TT 

•^ 

, 

^ 

s. 

\ 

\L- 

^■' 

-•^ 

>< 

Ct 

P 

n 

--V 

A 

d" 

^ 

fr. 

i-ji. 

z 

''H 

n-v 

=^" 

— 

'T 

^ 

^ 

'-' 

^s^r^  to  z  J| 

Fig.  12. — Nitrogen  content  of  apple  spurs  in  percentages  of  dry  weight,  bearing  spurs 
represented  by  continuous  lines  marked  W ,  B  and  /  for  Wealthy,  Ben  Davis  and  Jonathan 
respectively;  non-bearing  spurs  shown  by  broken  lines  marked  B  and  J;  barren  spurs 
represented  by  dot-dash  lines  marked  B  and  N  for  Ben  Davis  and  Nixonite.  {After 
Hooker. ^°<^) 


to  contain  1.52  per  cent,  of  nitrogen  in  the  winter  and  only  0.36  per  cent,  in  the 
spring.  Similarly  in  the  bark  of  Acer  platanoides  26  per  cent,  of  the  stored 
nitrogen  disappeared  from  winter  to  spring;  in  the  bark  of  the  cherry  37.16  per 
cent,  and  in  the  red  beech  30  to  50  per  cent,  disappeared  during  shoot  growth. 

The  nitrogen  that  is  moved  from  the  bark  into  the  blossoming  spur  passes  on 
into  the  developing  fruit,  so  that  in  the  biennially  bearing  spur  the  nitrogen 
content  decreases  as  long  as  the  fruit  is  attached.  Murneek^"  has  shown  recently 
that  the  total  nitrogen  content  of  apple  spurs  is  proportional  to  the  leaf  area  and 
that  it  decreases  as  a  result  of  defoliation. 

In  Fruit. — Though  the  nitrogen  of  the  fruit,  measured  in  percentages  of  dry 
weight,  decreases  throughout  development  on  account  of  the  increment  in  dry 
matter,  the  absolute  amount  present  increases  continuously.  Table  20  shows 
the  nitrogen  content  of  apples  in  percentages  of  dry  weight  and  in  absolute 
amounts. 


136  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Table  20. — Nitrogen  Content  of  Developing  Apples'" 


White  A.strakan 


Pleissner  Rambour 


Date 

Percent- 
age of  dry 
weight 

Grams  in 
1,000  fruits 

Date 

Percent- 
age of  dry 
weight 

Grams  in 
1,000  fruits 

Xvlay  29 

3.28 
2.20 
1.57 
1.21 
0.71 
0.51 
0.29 
0.37 
0.58 
0.23 

0.87 
3. 81 
9.75 
14.70 
15.00 
19.00 
16.60 
28.60 
23.40 
16.80 

June  2 

June  12 

June  22 

July  2 

July  12 

July  22 

Aug.  1 

Aug.  11 

Aug.  21 

Aug.  31 

Sept.  10 

Sept.  20 

Sept    30 

3.65 
2.78 
1.76 
1.26 
1.48 
0.54 
0.65 
0.63 
0.56 
0.39 
0.61 
0.66 
0.47 

1.12 

June  8 

June  18 

5.76 
11.40 

June  28 

19.70 

July  8 

July  18 

52.20 
34.20 

July  28     

56.00 

Aug.  7 

Aug.  17 

Aug.  27 

73.60 
59.20 
62.40 
91.20 
114.00 
86.40 

An  examination  of  the  graphic  presentation  in  Fig.  13  of  the  increase  in  the 
absolute  nitrogen  content  of  apples  and  pears  shows  that  the  increase  is  rapid 


\ 

/ 

/ 

\ 

/ 

r^ 

^^^ 

^' 

/^ 

f 

,^- 



*^ 

/; 

l^ 

■r=-=^ 

\ 

y^ 

^ 

/ 

^ 

"^^^ 

p= 

\ 

J 

u 

■f-'^ 

2& 


6         15       25        5        15       25       4-        14      24-       3        13       23       3 
May  June  July  Aug.  Sept.  Oct. 

Fig.   13. — Grama  of  nitrogen  in  one  thou.sand  fruits  of  the  apple  shown  by  broken  lines 
and  of  pears  shown  by  continuous  lines.      (Plotted  from  data  given  by  Pfeiffer.'^') 

at  first,  that  in  August  there  is  little  or  no  change  and  that  in  September  in  two  of 
the  apple  varieties,  there  is  a  second  period  of  increase.     These  periods  of  increas- 


INDI VI D UAL  ELEMENTS 


137 


ing  nitrogen  content  correspond  to  those  seasons  when  temperature  and  moisture 
conditions  are  such  as  to  favor  nitrification  in  the  soil. 

The  percentage  nitrogen  content  of  j^oung  fruit  is  very  high.  So  also  is  that 
of  the  seed,  to  which  in  fact  the  nitrogen  content  of  the  young  fruit  is  in  large 
part  due.  In  terms  of  drj'  weight,  the  nitrogen  content  of  apple  seeds  has  been 
found  to  be  3.17  per  cent.;  of  almonds  4  per  cent.;  of  coffee  {Coffeo  arabica)  beans 
1.96  per  cent.;  and  of  cocoanuts  1.65  per  cent.^* 

In  Various  Tissues  of  Trees  of  Different  Age. — A  studj'  of  the  nitrogen  content 
of  trees  of  various  ages  will  round  out  the  picture  of  nitrogen  distribution. 

Table  21  shows  the  percentages  of  nitrogen  in  the  leaves,  new  growth,  trunk, 
roots  and  fruit  of  apple  trees  of  ages  ranging  from  1  to  100.  Since  the  material 
was  collected  from  various  sources,  the  analyses  are  not  strictly  comparable, 
though  they  are  suggestive. 


Table  21. — Analyses  of  Apple  Trees 
(1  to  9  from  Thompson,^^^  13  and  100  from  Roberts,^^'  30  from  Van  Slyke  i*") 
A  Nitrogen  in  percentage  of  dry  weight.     B  Absolute  amounts  of  nitrogen  in 
gram.s. 


Age 

Leaves 

New  gi-owth 

Trunks    and 
branches 

Roots 

Fruit 

A 

B 

A 

B 

A 

B 

A 

B 

A 

B 

1 

1.71 

0.44 

0.30 

0.29 

0.39 

0.20 

2 

2.09 

1.51 

0.57 

1.36 

0.88 

1.14 

3 

2.36 

2.08 

0.52 

4.00 

0.73 

3.29 

4 

1.66 

2.24 

0.45 

6.35 

0.59 

2.99 

5 

1.76 

7.84 

0.89 

1.93 

0.48 

17.20 

0.64 

9.85 

6 

1.74 

10.50 

0.94 

2.41 

0.39 

16.60 

0.62 

17.70 

.... 

7 

1.45 

13.60 

0.84 

3.66 

0.45 

30.55 

0.64 

26.10 

0.35 

4.34 

8 

1.74 

41.00 

0.93 

6.06 

0.36 

45.30 

0.62 

47.70 

0.43 

5.93 

9 

1.70 

61.50 

0.82 

9.08 

0.35 

85.50 

0.58 

81.00 

0.31 

10.55 

13 

1.85 
2.09 
1.04 

131.50 
394 . 00 
435.00 

30 

0.95 
1.04 

13.60 
390.00 

0.31 

258  00 

100 

0.27 

2863.00 

0.22 

417.00 

These  figures  show  that  the  young  tree  is  specially  rich  in  nitrogen.  The 
roots  have  a  higher  percentage  content  than  the  trunk,  but  a  lower  content  than 
the  new  growth.  The  percentage  nitrogen  content  of  both  roots  and  trunk  falls 
to  a  very  low  level  in  the  100-year  old  tree,  due  to  the  great  preponderance  of 
woody  tissue.  That  of  the  leaves  was  estimated  from  samples  collected  in  the 
fall  and  consequently  is  probably  too  low,  except  in  the  case  of  the  100-j^ear  old 
tree,  where  the  sample  was  taken  in  July. 

The  most  striking  observation  to  be  made  concerns  the  large  proportion  of 
the  total  nitrogen  of  the  plant  that  is  in  the  leaves,  roughly  about  one-fourth  in 
trees  up  to  9  years  of  age.  Since  these  figures  represent  the  amounts  at  leaf  fall, 
even  larger  amounts  must  be  present  in  the  leaves  during  the  summer. 


138 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


From  the  data  available  it  is  impossible  to  say  how  much  of  the  nitrogen  of 
the  trunk  is  stored  and  how  much  is  a  permanent  part  of  its  tissues.  Hence  any 
attempt  to  calculate  the  amount  taken  up  yearly  from  the  soil  would  be  guess- 
work. However,  it  is  interesting  that  in  a  30-year  old  tree,  two-thirds  as  much 
nitrogen  goes  into  the  crop  as  falls  with  the  leaves  and  the  amount  used  for  new 
growth  is  insignificant  in  comparison. 

Similar  relationships  hold  for  fruits  other  than  the  apple  as  Table  22  shows. 


Table 


-Pounds  of  Nitrogen  in  Parts  of  a  Full  Grown  Tree'^" 


Apple 


Peach 


Pear 


Plum        Quince 


Fruit  or  fruit  pulp 

Stones 

Stems 

Leaves 

New  growth 


0.57 

0.12 

0.08 

0.08 

0.03 

.... 

0.02 
0.01 

0.87 

0.52 

0.15 

0.12 

0.03 

0.05 

0.02 

0.02 

0.09 


0.09 
0.01 


The  data  presented  in  Table  23  show  the  nitrogen  contents  of  various  fruits. 


Table   23 

Almonds 

Apricots 1 .  94 

Apples 1 .  05 

Bananas 0.97 

Cherries 2.29 

Chestnuts 6.40 

Figs 2.38 

Grapes 1.26 


Pounds   of   Nitrogen  in   1,000  Pounds   of   Fresh  Fruit^^ 

7.01     Lemons 1.51 

Olives 5.60 

Oranges 1 .  83 

Peaches 1.20 

Pears 0.90 

French  primes 1 .  82 

Plums 1.81 

Walnuts 5.41 


PHOSPHORUS 

It  has  been  pointed  out  that  the  nitrates  absorbed  by  the  roots 
probably  are  carried  to  the  leaves  and  there  elaborated  into  organic  nitro- 
gen-containing compounds.  Though  there  is  no  direct  evidence  to  show 
where  the  elaboration  of  inorganic  phosphates  to  organic  phosphorus- 
containing  compounds  takes  place,  the  remarkable  similiarity  that  exists 
between  the  variations  in  nitrogen  and  in  phosphorus  content  of  practi- 
cally all  tissues,  suggests  that  phosphorus,  like  nitrogen,  is  elaborated  for 
the  most  part  in  the  leaf. 

Synthesis  of  Phosphorus-containing  Organic  Compounds. — The 
amount  of  phosphorus  assimilated  is  stated  to  be  closely  related  to  the 
amount  of  illumination ^^^  the  plant  receives  and  appears  to  be  connected 
with  photosynthetic  activity.  Red  and  yellow  light  have  been  found 
more  effective  than  blue  or  violet  in  promoting  phosphorus  assimilation. ^^^ 

Wherever  phosphorus  is  found  in  organic  combination  it  exists  as 
phosphate.     Thus  it  occurs  in  nucleic  acids,  nucleins  and  nucleo-proteins 


INDIVIDUAL  ELEMENTS 


139 


— substances  always  present  in  the  cell  nucleus — in  lecithins,  in  hexose 
phosphoric  acid  which  is  essential  to  zymase  activity  in  yeast  and  prob- 
ably to  the  activity  of  similar  enzymes  in  all  plant  tissues.  The  globoid 
in  aleurone  grains  is  composed  of  calcium-magnesium  phosphate.       / 

Translocation  and  Use  of  Phosphorus-containing  Compounds. — The 
distribution  of  phosphorus  in  the  fruit  tree  is  very  similar  to  that  of 
nitrogen.  Young  tissue  is  richer  in  phosphorus  than  older  tissue,  young 
leaves  and  young  bark  being  particularly  rich  in  this  element  and  much 
the  same  relations  hold  in  regard  to  elaboration,  storage  and  utilization 
of  phosphorus  as  with  nitrogen.  Most  tissues  contain  approximately 
six  times  as  much  nitrogen  as  phosphorus.  This  holds  roughly  for 
trunk  and  branches,  new  growth,  buds  and  young  leaves.  The  older 
leaves  have  less  phosphorus,  the  fruit  and  the  apple  spur  more.  The 
general  constancy  of  the  phosphorus-nitrogen  ratio  indicates  that  the 
two  elements  may  be  combined  in  the  same  molecule.  Nucleins,  nucleo- 
proteins  and  lecithin  contain  both  elements  and  are  of  universal  occur- 
rence in  all  living  plant  tissues.  Table  24  shows  the  relative  amounts  of 
the  various  types  of  organic  phosphorus  in  developing  grape  seeds.  The 
bulk  is  nuclein  phosphorus  and  should  this  be  the  case  in  most  plant 
tissues  the  relative  constancy  of  the  nitrogen-phosphorus  ratio  would 
be  explained. 


Table  24. 


-The  Phosphorus  Content  of  Grape  Seeds'' 
(In   percentages   of  fresh   weight) 


Hard,  Sept.  6 


Softening,  Sept. 
30 


Ripe,  Oct.  30 


Lecithin  P.  .  . . 
Nuclein  P. . . . 
HCl-soluble  P 


0.0017 
0.0159 
0.0019 

o.oinr, 


o.oois 

0.0184 
0.0016 

0.0218 


0.0021 
0.0197 
0.0016 

0.0234 


Nevertheless  distinct  differences  exist  between  the  variations  in  the 
nitrogen  and  in  the  phosphorus  content  of  the  same  tissue  and  these 
show  that  phosphorus  compounds  do  not  play  the  same  part  in  plant 
metabolism  as  nitrogen  compounds. 

If  organic  phosphorus-containing  compounds  are  built  up  chiefly  in 
the  leaves,  they  pass  out  of  the  leaves  as  fast  as  they  are  made  and  are 
used  by  the  developing  fruit  and  in  the  growth  of  vegetative  tissues. 
Before  the  leaves  fall,  a  considerable  amount  of  their  phosphorus  is 
withdrawn  and  stored  in  the  phloem.  The  phosphorus  used  in  the  first 
stages  of  growth  in  the  spring  and  in  the  initiation  of  fruit  development  is 
obtained  from  stored  compounds. 


140 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Amounts  Used  in  Fruit  Production. — In  general  the  tree  may  be  said 
to  require  relatively  large  amounts  of  phosphorus  for  fruit  production, 
much  larger  than  for  mere  vegetative  growth.  However,  analyses  would 
indicate  that  the  total  amount  required  by  the  trees  for  the  development 
of  their  fruits  and  of  their  new  vegetative  tissue  would  not  be  more  than 
8  pounds  per  acre  in  a  peach  orchard  yielding  at  the  rate  of  300  bushels; 
the  total  phosphorus  draft  of  most  other  deciduous  fruits  is  not  materially 
greater.  Considering  the  limited  amounts  of  phosphorus  used  by  decidu- 
ous fruit  trees,  and  the  comparatively  large  amounts  present  in  nearly 
all  soils  as  well  as  the  supply  in  the  subsoil  available  to  deep-rooted  trees, 
it  is  evident  that  under  average  orchard  conditions  phosphorus  is  not 
likely  to  be  a  limiting  factor  and  that  phosphorus  fertilization  is  likely 
to  be  of  little  direct  use  in  assisting  tree  growth  or  in  promoting  fruit 
production.  On  the  other  hand  it  may  be  of  great  value  in  promoting 
the  growth  of  grasses,  legumes  or  other  crops  grown  between  the  trees 
for  mulching  or  other  purposes.  This  subject  is  discussed  in  some  detail 
under  the  heading  of  indirect  methods  of  fertilization. 

Seasonal  Distribution  of  Phosphorus. — There  is  a  close  similarity 
between  the  seasonal  distribution  of  phosphorus  and  nitrogen  in  many 
parts  of  the  fruit  tree. 


0.5 


0.3 


\ 

1 

1 
1 

^s 

\ 

1 
1 
1 

1 

1 

Fig.  14. 


-Phosphorus  content  of  plum  leaves  in  percentages  of  dry  weight.     (Plotted 
from  data  given  by  Richter.i^*) 


In  Leaves. — Though  leaf  buds  have  a  slightly  higher  percentage  nitrogen 
content  than  fruit  buds,  they  have  a  sKghtly  lower  percentage  of  phosphorus. 
The  phosphorus  content  of  the  former  has  been  found  to  be  0.576  per  cent,  of  the 
dry  weight  in  the  cherry  and  0.594  per  cent,  in  the  plum;  of  the  latter,  0.570 
per  cent,  in  the  cherry  and  0.592  per  cent,  in  the  plum.'^* 

The  young  leaf  has  about  the  same  high  percentage  of  phosphorus  as  the  bud, 
but  this  decreases  rapidly  with  age  as  does  the  nitrogen,  there  being  two  periods 
of  rapid  decUne,  one  in  May,  the  other  in  September  (see  Table  25  and  Figure  14). 
The  ratio  of  phosphorus  to  nitrogen  in  the  young  leaf  is  1  :  6.  Before  leaf  fall 
it  is  1  :  10  or  1  :  15.     This  indicates  that  the  plant  uses  its  phosphorus  supply 


INDIVIDUAL  ELEMENTS 


141 


more  thoroughly  than  its  nitrogen,  withdrawing  it  more  completely  from  tissues 
that  are  exfoliated  and  either  using  it  immediately  in  tissue  building  or  storing  it. 

Table  25. — The  Phosphorus  Content  of  Leaves^^* 
(In  percentages  of  dry  weight) 


Apple 


May  9,  14,  18 

June  22 

Aug.  29 

Sept.  30,  Oct.  2,  15 


0.566 
0.245 
0.207 
0.126 


Pear 


0.595 
0.181 
0.177 
0.069 


Cherry 


0.602 
0.302 
0.329 
0.273 


Plum 


0.510 
0.305 
0.289 
0.197 


The  absolute  amounts  of  phosphorus  in  leaves  of  various  ages  are  shown  in 
Table  26.  As  with  nitrogen,  the  total  amount  of  phosphorus  in  the  leaf  is  low  at 
first,  despite  the  high  percentage,  becau.se  of  the  small  size  of  the  leaf.  It  then 
increases  as  the  leaf  grows,  reaches  a  maximum  and  finally  decUnes,  the  dechne, 
however,  coming  only  a  short  time  before  abscission. 

T.\BLE  26. — Grams  of  Phosphorus  in  100  Le.wes'^* 


Apple 


Pear 


Cherry 


Plum 


July  14 

July  31 

Aug.  18,  21 

Sept.  3,  4,  6 

Oct.  23,  27,  29,  Nov.  4. 


0.036 
0.043 
0.034 
0.034 


0.072 
0.069 
0.068 
0.061 
0.061 


0.054 
0.049 
0.049 
0.044 


In  the  work  from  which  this  table  is  computed  the  possibihty  of  loss  of  nutri- 
ent elements  by  cUmatic  agencies  was  considered.  Le  Clerc  and  Breazeale'*^ 
caUed  attention  to  the  possibility  that  plant  tissue  may  lose  considerable  amounts 
of  mineral  constituents  through  the  dissolving  action  of  rain.  In  this  way 
apple  leaves  attached  to  the  branches  lost  3  per  cent,  of  their  nitrogen, 
25  per  cent,  of  their  phosphorus,  18  per  cent,  of  their  potash. and  6  per  cent,  of 
their  Ume  simply  by  washing  in  water.  This  indicates  that  considerable  amounts 
of  soluble  substances  exuded  from  the  surface  may  be  washed  off  the  leaves  during 
the  period  between  the  formation  of  the  abscission  layer  and  the  time  of  actual 
leaf  fall. 

In  Branches,  Trunk  and  Roots. — The  percentage  of  phosphoric  acid  (P2O5)  in 
the  ash  of  sap-wood  is  usually  higher  than  in  bark  ash;  for  example,  in  the  pear  it 
has  been  recorded  as  12.62  per  cent,  in  the  sap-wood,  as  2.98  per  cent,  in  the  bark 
and  in  the  grape  7.625  per  cent,  in  the  sap-wood  and  4.705  per  cent,  in  the  bark.«* 

This  does  not  mean,  however,  that  the  bark  contains  less  phosphorus  than  the 
sap-wood,  for  as  has  been  pointed  out,  the  total  ash  content  of  wood  and 
especially  sap-wood  is  much  less  than  that  of  bark.  The  figures  indicate  that 
though  the  sap-wood  contains  relatively  large  percentages  of  phosphoric  acid,  in 
the  pear  and  grape  at  least  the  bark  contains  larger  absolute  amounts. 


142 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Table  27.- 


-The  Phosphorus  Content  of  a  7-year  Old  Apple  Tree^^ 
(Expressed  in  percentages  of  dry  weight) 


Dormant, 

Dec.  3, 

1914 

Buds 
swelling, 
April  20, 

1915 

In  bloom. 

May  18, 

1915 

Growth 
over,  July 
12,    1915 

Leaves 

faUing, 

Oct.  12, 

1915 

Summer's  growth 

1-year  old  branches 

2-year  old  branches 

3-year  old  branches 

4-year  old  branches 

5-year  old  branches 

Trunk 

Large  roots 

0.14 
0.11 
0.08 
0.07 
0.05 
0.04 
0.10 
0.16 

0.16 
0.11 
0.10 
0.07 
0.06 
0.06 
0.12 
0.17 

0.10 
0.07 
0.06 
0.05 
0.04 
0.04 
0.09 
0.14 

0.14 
0.10 
0.08 
0.07 
0.06 
0.05 
0.06 
0.11 
0,14 

0.13 
0.10 
0.08 
0.07 
0.06 
0.05 
0.06 
0.12 
0.17 

Phosphorus,  like  nitrogen,  is  present  in  greatest  amounts  in  the  younger 
roots  and  branches  and  is  at  a  maximum  in  nearly  all  tissues  when  the  buds  are 
swelling  (see  Table  27).     The  chief  difference  between  phosphorus  and  nitrogen 

035 


0.30 


o.es 


0.20 


0.15 


0.10 


/ 

\ 

/ 

\ 

/ 

IV 

\ 

J 

^ 

^ 

<^ 

X, 

\\ 

i^^ 

^ 

N. 

J 

^3- 

\ 

h> 

v. 

\N 

^ 

Ji 

^ 

\ 

/ 

>^ 

!S 

^^ 

,. 

-^ 

y. 

^ 

>5 

\ 

\ 
\ 

'/ 

N 

-^ 

J 

^- 

^^ 

J 

Bv 

\ 

V; 

U 

■*- 

---- 

-^ 

r-* 

. 

--■ 

\ 

\ 

7 

y 

-'" 

\ 

V 

Fig.  15. — Phosphorus  content  of  apple  spurs  in  percentages  of  dry  weight;  bearing 
spurs  represented  by  continuous  lines,  non-bearing  spurs  by  broken  lines  and  barren  spurs 
by  dot-dash  lines.      {.After  Hooker y^'^) 

is  that  phosphorus  reaches  a  minimum  in  most  tissues  in  May  when  the  tree  is 
in  bloom,  while  nitrogen  does  not  reach  a  minimum  until  July  when  active  growth 
is  over.  In  all  woody  tissues  there  is  an  accumulation  of  phosphorus,  as  of  nitro- 
gen, in  the  fall,  indicating  storage. 

In  Spurs. — Figure  15  shows  the  seasonal  variations  in  the  phosphorus  content 
of  apple  spurs.  100  In  non-bearing  and  in  barren  spurs,  the  variations  are  similar 
to  those  in  other  woody  tissues,  with  a  minimum  in  May.     However,  in  June 


INDIVIDUAL  ELEMENTS 


143 


during  the  period  of  fruit  bud  differentiation  there  is  a  marked  increase  which  is 
particularly  pronounced  in  spurs  differentiating  fruit  buds.  Phosphorus  accu- 
mulation in  the  fall  is  well  marked,  especially  in  productive  spurs. 

In  bearing  spurs  there  is  a  considerable  increase  in  phosphorus  during 
blossoming,  indicating  that  these  organs  draw  upon  a  supply  of  stored  phos- 
phorus, which  may  be  assumed,  by  analogy  with  nitrogen,  to  be  in  the  bark. 
Moreover,  the  phosphorus  content  of  bark  is  at  a  maximum  in  the  spring. 

In  Fruit. — As  soon  as  the  fruit  begins  to  develop,  the  phosphorus  content 
of  the  bearing  spur  decreases.  At  this  time  the  spur  probably  is  supplying  the 
young  fruit  with  phosphorus,  which  accumulates,  to  a  considerable  extent,  in 
fruits  and  seeds.  This  increase  is  illustrated  by  the  figures  in  Table  28  showing 
the  amounts  in  ripening  grapes. 

Table  28. — Grams  of  Phosphorus  in  1,000  Berries  of  the  Grape*'* 

July  27 0.169  Sept.  17 0.434 

Aug.  9 0.315  Sept.  28 0.550 

Aug.  17 0.262  Oct.  5 0.619 

Aug.  28 0.206  Softening  Oct.  12 0.455  Fully  ripe 

Sept.  7 0.373  Oct.  22 0.320  Rotten 

In  Various  Tissues  of  Trees-  of  Different  Ages. — The  percentages  and  absolute 
amounts  of  phosphorus  in  the  tissues  of  apple  trees  of  various  ages  is  shown  in 
Table  29.  In  general  the  new  growth  and  the  leaves,  even  at  the  time  of  leaf 
fall,  are  richest  in  phosphorus,  the  fruit  next,  then  the  roots;  the  trunk  and  older 
branches  have  the  least. 


Table  29. — Phosphorus  Content  of  Apple  Trees  of  Various  Ages 
(1  lo  9  computed  from  Thompson,^^^  13  and  100  from  Roherts,^^''  30  from  Van  Slyke^^°) 


Leaves 

New  Growth 

Trunk  and 
branches 

Roots 

Fruits 

Age 

Per  cent. 

Per  cent. 

Per  cent. 

Per  cent. 

Per  cent. 

dry 

Grams 

dry 

Grams 

dry 

Grams 

dry 

Grams 

dry 

Grams 

weight 

weight 

weight 

weight 

weight 

1 

0.12 

0.03 

0.03 

0.03 

0.03 

0.02 

2 

0.13 

0.10 

0.07 

0.17 

0.10 

0.13 

3 

0.14 

0.13 

0.07 

0.50 

0.11 

0.47 

4 

0.10 

0.13 

0.06 

0.80 

0.06 

0.31 

5 

0.11 

0..51 

0.11 

0.24 

0.05 

1.96 

0.06 

1.00 

6 

0.10 

0.63 

0.13 

0.34 

0.04 

1.85 

0.07 

1.99 

7 

0.10 

0.90 

0.11 

0.47 

0.06 

4.14 

0.06 

2.48 

0.08 

1.03 

8 

0.11 

2.68 

0.13 

0.82 

0.05 

6.03 

0.07 

5.33 

0.08 

1.44 

9 

0.15 

5.33 

0.15 

1.64 

0.08 

19.15 

0.09 

12.62 

0.07 

2.38 

13 

0.21 

15.83 

30 

0.13 

27.70 

0.13 

2.00 

0.6 

49.00 

100 

0.17 

73.20 

0.16 

61.40 

0.04 

705.00 

0.04 

83.00 

Of  particular  interest  is  the  comparison  of  the  absolute  amounts  of  phosphorus 
in  the  fruit  and  leaves  with  the  nitrogen  content  of  these  tissues.  In  a  30-year 
old  tree  in  full  bearing  more  phosphorus  is  lost  with  the  crop  of  fruit  than  falls 
with  the  leaves,  even  if  it  be  assumed  that  25  per  cent,  of  the  original  amount  was 


144 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


removed  by  the  dissolving  action  of  rain.  This  is  true  of  many  fruit  trees,  as 
Table  30  shows. ^^^  This  relation  does  not  hold  for  young  trees  just  in  bearing. 
That  more  phosphorus  is  lost  in  the  crop  than  with  the  leaves  of  mature  trees 
may  be  attributed  to  several  factors.     As  has  been  emphasized,   only  one-tenth 

Table  30. — Pounds  of  Phosphorus  in  Parts  of  a  Full  Grown  Tree'^o 


Apple 

Peach 

Pear 

Quince 

Plum 

0.105 



0.061 
0.004 

0.026 
0.004 
0.031 
0.004 

0.013 

0,017 



0.013 

Stones 

0.004 

0.008            0.004 

0.008 

New  growth 

0.004 

0  004 

0.004 

to  one-fifteenth  as  much  phosphorus  as  nitrogen  is  left  in  the  leaf,  but  the  fruit 
contains  one-fifth  as  much  phosphorus  as  nitrogen.  This  in  turn  may  be  cor- 
related with  the  finding  that  the  phosphorus  content  of  leaves  on  peach  trees 
in  heavy  bearing  is  less  than  that  of  the  leaves  on  trees  bearing  a  small  crop.^*'^ 

Table  31. — Phosphorus  Content  of  Peach  Leaves  in  Bearing  and  Non-bearing 

Years'" 
(Percentage  of  dry  weight) 

First  four  years 0 .  30 

Five  years  of  bearing 0 .  24 

1904  (no  crop) 0.29 

The  data  in  Table  29  suggest  that  this  may  hold  for  the  apple  as  well  as  the  peach. 
Table  32  gives  the  phosphorus  content  of  various  fruits  in  absolute  amounts.  It 
is  present  in  seeds  in  greater  amounts. 

Table  32. — Pounds  of  Phosphorus  in  1,000  Pounds  of  Fresh  Fruit^" 


Almonds 0.45 

Apricots 0 .  29 

Apples 0.14 

Bananas 0 .  07 

Cherries 0.31 

Chestnuts 0.52 

Figs 0.38 

Grapes 0.05 


Lemons 0 .  25 

Olives 0.55 

Oranges 0.23 

Peaches 0 .  37 

Pears 0.15 

French  prunes 0.30 

Plums 0.33 

Walnuts 0.65 


POTASSIUM 

Though  the  history  of  potassium  in  a  fruit  tree  like  the  apple  is  in 
many  respects  similar  to  that  of  phosphorus,  there  are  important 
differences. 

S3mthesis,  Translocation  and  Use  of  Potassium-containing  Com- 
pounds.— It  is  not  known  where  potassium  is  elaborated  and  there  is  no 
evidence  to  show  that  the  inorganic  potassium  taken  from  the  soil  by 
the  roots  is  combined  in  organic  form  in  the  leaves  to  any  greater  extent 
than  in  any  other  part  of  the  plant.  In  just  what  form  of  organic  com- 
bination potassium  is  necessary  for  the  proper  activity  of  the  plant  is  also 


INDIVIDUAL  ELEMENTS  145 

unknown.  However,  certain  proteins  crystallize  as  potassium  salts; 
sinigrin  is  myronate  of  potash.  Complex  salts  of  calcium,  magnesium 
and  potassium  are  not  uncommon.  Gum  arable  contains  a  calcium- 
magnesium-potassium  salt  of  arable  acid. 

During  the  winter,  potassium  is  stored  in  both  the  sap  wood  and  bark 
and  in  older  branches  than  nitrogen  or  phosphorus.  In  the  spring,  it  is 
translocated  and  used  in  the  development  of  new  tissue,  but  preeminently 
for  fruit  and  then  for  leaves.  Heavy  crops  reduce  the  potassium  content 
of  the  leaves  and  much  more  potassium  goes  into  the  fruit  than  is  lost 
with  the  leaves.  In  general  wherever  potassium  is  present  in  large 
amounts  as  in  seeds  and  in  young  tissue,  calcium  is  present  in  small 
quantities  and  wherever  there  Is  a  small  amount  of  potassium,  calcium  Is 
present  in  large  amounts. 

The  Demand  and  the  Supply. — In  one  way  or  another  the  idea  has 
gained  credence  that  fruit  trees  make  heavy  demands  on  the  soil  for 
potash  and  consequently  that  potash  is  one  of  the  most  necessary  in- 
gredients in  fertilizers  for  orchards.  Indeed,  so  firmly  has  this  Idea 
become  estabUshed  that  "  Fertilize  trees  with  nitrogen  for  wood  growth 
and  with  potash  for  fruit  production"  is  a  time-honored  recommendation 
In  the  literature  of  fruit  growing.  It  has  also  been  a  rather  general 
opinion  that  potash  mainly  is  responsible  for  the  red  coloration  of  fruits 
and  that  consequently  potash-carrying  fertilizers  are  especially  desirable 
for  Improving  color.  That  this  last  idea  is  erroneous  is  shown  by  the 
results  of  many  carefully  conducted  Investigations  of  recent  years,  in- 
vestigations that  are  reported  In  more  detail  later  in  this  section.  The 
data  in  this  chapter  afford  some  idea  of  the  approximate  amounts  of 
potash  that  are  required  for  usual  tree  growth  and  production.  Though 
these  are  considerable  in  comparison  with  the  amounts  required  by 
many  farm  crops,  the  enormous  quantities  of  this  element  found  within 
reach  of  tree  roots  in  most  soils  make  the  application  of  potash-carrying 
fertilizers  seem  of  doubtful  promise,  at  least  so  far  as  supplying  the  plant 
with  larger  quantities  of  this  element  is  concerned.  This  statement  is 
supported  by  numerous  experiments  In  which  potash  in  different  forms 
has  been  applied  to  orchard  trees  apparently  without  positive  results, 
and  also  by  soil  investigations  like  those  of  Hopkins  and  Aumer,i°^ 
showing  that  in  6  feet  of  soil  covering  an  area  of  1  square  mile  of  the 
Illinois  corn  belt  there  Is  as  much  potash  as  is  applied  annually  in  fertil- 
izers to  all  the  farms  of  the  United  States.  It  is  true  that  many  orchard 
soils  are  not  so  liberally  supplied  with  potash  as  those  of  the  Illinois  corn 
belt;  nevertheless,  so  far  as  data  are  available,  they  indicate  the  presence 
of  quantities  much  in  excess  of  probable  requirements  for  many  years, 
if  not  for  many  generations.  Beneficial  results  in  greater  vegetative 
growth  and  Increased  yields  have  been  reported  occasionally  from  the 
application  of  potash-carrying  fertilizers  to  orchard  soils.     The  question 


146 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


m"ay  be  raised,  whether  this  increase  in  growth  or  yield  is  not  due  to 
indirect  effects  of  the  potash  on  some  other  factor,  such  as  the  availa- 
bihty  of  phosphorus,  or  to  the  influence  of  other  elements  with  which 
potassium  is  combined  in  the  fertilizer.  This  last  suggestion  receives 
some  support  from  the  fact  that  in  most  cases  when  the  muriate  and 
sulfate  of  potash  have  been  used  side  by  side,  the  sulfate  has  almost 
invariably  given  a  much  more  pronounced  response  than  the  muriate  and 
has  often  yielded  positive  results  when  the  muriate  has  given  entirely 
negative  results. 

Seasonal  Distribution  of  Potassium. — Rather  marked  differences  between 
potassium  and  the  elements  already  considered,  in  translocation,  storage  and 
utilization  are  shown  by  the  seasonal  changes  in  its  distribution  within  the  plant. 

In  Leaves. — Fruit  buds  are  much  richer  than  leaf  buds  in  potassium  con- 
trasting with  the  condition  presented  by  phosphorus. 

The  potash  content  of  fruit  buds  has  been  found  to  be  2.290  per  cent,  of  the 
dry  weight  in  the  cherry  and  2.344  per  cent,  in  the  plum,  while  that  of  leaf  buds 
was  1.961  per  cent,  in  the  cherry  and  2.213  per  cent,  in  the  plum.^^'^ 

The  variation  in  the  percentage  content  of  potash  in  leaves  during  the  growing 
season  is  illustrated  by  the  figures  in  Table  33.  As  with  phosphorus  and  nitrogen 
the  percentage  of  potassium  decreases  as  the  leaf  grows  older  and  the  absolute 
amount  present  in  the  leaf  passes  through  a  maximum,  as  Table  34  shows. 


Table 
(Ir 

33. — Potash  Content  of  Leaves 
I  percentage  of  dry  weight'"'^) 

Apple 

Pear 

Cherry 

May  9 

May  14 

3.150 

1.886 
1.927 

1.601 

2.460 

1.690 
1.770 
1 .  320 

3  006 

June  22 

2  782 

Aug.  29 

Oct.  2 

Oct.  15 

2.637 

3 .  080 

However,  the  decrease  in  the  potash  content  of  leaves  during  the  fall  is  slight 
in  all  fruits  for  which  data  are  available  and  there  is  no  decrease  in  the  pear.     The 

Table  34. — Grams  of  Potash  in  100  Leaves '^^ 


Plum 


INDIVIDUAL  ELEMENTS  147 

marked  difference  in  this  respect  between  potassium  and  phosphorus  or  nitrogen 
suggests  a  corresponding  difference  in  their  utihzation  by  the  plant.  Possibly 
the  elaboration  of  potassium  is  not  localized  in  the  leaf. 

Though  the  amounts  of  potassium  removed  from  the  leaves  before  they  fall 
seem  small  in  comparison  with  phosphorus,  there  is  none  the  less  evidence  of 
potassium  storage  in  the  branches.  Table  35  gives  data  showing  the  withdrawal 
of  potash  from  the  leaves  into  the  branches. 

Table  35. — Grams  of  Potash  in   100  Branches  of  the  Horse-chestnut  and 
Their  Leaves* 

Branches  Leaves 


July  29 1.763 

Sept.  11 2.249 

Oct.  14 2.575 

Nov.  16 I  2.671 


18.876 
14 . 236 
13.400 


In  Branches,  Roots  and  Trunks. — The  leaves  lose  more  potassium  than  can  be 
accounted  for  by  the  gain  in  the  branches  on  which  they  were  borne,  indicating 
that  considerable  amounts  of  potash  are  washed  from  the  leaves  by  rain.  The 
relative  amounts  of  potash  in  the  ash  of  sap-wood  and  bark  resemble  those  of 
phosphorus.  In  one  series  of  determinations  the  ash  of  the  sap-wood  of  the  pear 
was  22.25  per  cent,  potash,  of  the  bark  6.2  per  cent.;  the  sap-wood  ash  of  the 
apple  was  16.19  per  cent,  potash,  the  bark  ash  4.93  per  cent,  and  the  sap-wood 
ash  of  the  grape  was  20.84  per  cent,  potash,  the  bark  ash  1.77  per  cent.^^  In 
the  sap-wood  ash  there  is  more  potash  than  any  other  element  except  calcium ;  in 
the  bark  the  potash  content  is  lower  and  the  calcium  content  higher,  but  the 
absolute  amount  in  the  bark  is  probably  greater  than  in  the  sap-wood  on  account 
of  the  bark's  higher  ash  content,  as  has  been  pointed  out  in  the  discussion  of 
phosphorus. 

Table  36,  showing  seasonal  variations  in  the  potash  content  of  the  root,  trunk 
and  branches  of  a  7-year  old  apple  tree,  gives  additional  evidence  of  the  storage 
of  potassium  in  the  branches. 

Apparently  potassium  is  stored  in  old  branches  to  a  relatively  greater  extent 
than  nitrogen  or  phosphorus,  for  in  the  3-,  4-  and  5-year  old  branches  the  potash 
content  reaches  a  minimum  in  May  though  the  1-  and  2-year  old  branches  have  a 
high  content  at  that  time  and  do  not  reach  a  minimum  until  later.  The  young 
roots  and  branches  are  richer  in  potassium,  as  in  phosphorus  and  nitrogen,  than 
the  older  parts  of  the  tree. 

Potassium  probably  is  stored  in  both  bark  and  sap-wood.  The  layers  of 
bark  nearest  the  cambium  are  richest  in  this  element.  Furthermore,  the  young 
bark  of  the  oak,  horse-chestnut  and  walnut  contains  more  potash  in  percentage 
of  total  ash  at  the  time  of  greatest  vegetative  activity  in  the  spring  than  later  in 
the  season. ^2  Similar  seasonal  differences  oc(iur  in  the  potash  content  of  the  sap- 
wood  of  these  trees,  while  the  heart-wood  not  only  contains  considerably  less  but 
its  content  is  subject  to  much  smaller  fluctuations."  Weber^^^  found  that  in 
beeches  producing  many  seeds,  the  sap-wood  was  particularly  rich  in  potash 


148 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Table  36. — The  Potash  Content  of  a  7-year  Old  Apple  Tree 
(Expressed  in  percentages  of  dry  weight") 


Dormant, 
Dec.  3 

Buds 
swelling, 
Apr.  20 

In  bloom. 
May  18 

Growth 

over, 
July  12 

Leaves 
falling, 
Oct.  12 

Summer's  growth 

1-year  old  branches 

2-year  old  branches 

3-year  old  branches 

4-year  old  branches 

5-year  old  branches 

Trunk                      

0.46 
0.33 
0.30 
0.24 
0.20 
0.15 
0.42 
0  57 

.... 
0.49 
0.33 
0.27 
0.25 
0.22 
0.21 
0.40 
0.45 

0.62 
0.39 
0.28 
0.20 
0.17 
0.20 
0.39 
0.45 

1.03 
0.52 
0.33 
0.31 
0.25 
0.20 
0.18 
0.43 
0.54 

0.60 
0.47 
0.40 
0.33 
0.29 
0.28 
0.25 

Large  roots 

0.40 
0.65 

while  the  phosphorus  content  was  not  materially  greater  than  in  trees  bearing 
few  seeds.  Warren^^''  found  that  in  peach,  apple,  plum  and  pear  trees  the  ash  of 
the  leaves  contained  less  potash  in  years  when  the  crop  was  large  (see  Table  37). 

Table  37. — The  Potash  Content  op  Peach  Leaves  in  Bearing  and  Non-bearing 

Years'" 


In  percentages  of 
dry  matter 

In  percentages  of 
total  ash 

First  four  years 

Five  bearing  years 

1904  (no  crop) 

2.12 
1.42 
1.80 

17.7 
11.2 
15.8 

This  suggests  that  fruit  trees  usually  take  up  more  potassium  from  the  soil  than 
is  actually  required,  when  they  are  not  bearing  fruit. 


2:  5: 


Fig.  16. — Potassium  content  of  apple  spurs  in  percentages  of  dry  weight;  bearing 
spurs  represented  by  continuous  lines,  non-bearing  spurs  by  broken  lines  and  barren  spurs 
by  dot-dash  lines.     (After  Hooker.'^°°) 

hi  Spurs.— Figure  16  shows  that  the  potassium  content  of  bearing  spurs  rises 
to  a  very  high  maximum  in  May.     This  increment  passes  into  the  fruit  and  the 


INDIVIDUAL  ELEMENTS 


.  149 


potassium  content  of  the  spur  falls  to  a  minimum  in  September.  The  low  figure 
for  barren  spurs  throughout  the  year  is  noteworthy,  as  is  also  the  increase  in  the 
potassium  content  of  spurs  in  the  off  year  at  the  time  when  fruit  buds  are  being 
differentiated  (June). 

In  Fruit. — The  data  in  Table  38  illustrate  the  increase  in  i-)otash  content 
accompanying  fruit  development. 


Table   38 
July  27 


-Grams  of   Potash   in    1,000   Berries  of  the   Grape' 


J . 875 

Aug.  9 2.306 

Aug.  17 2.490 

Aug.  28  (softening) 2 .  194 

Sept.  7 4.288 


Sept.  17 4..824 

Sept.  28 5.588 

Oct.  5 6.179 

Oct.  12  (fully  ripe) 4.924 

Oct.  22  (rotted) 4.317 


The  leaves,  fruit  and  seeds  are  the  parts  richest  in  potassium  (see  Table  40). 
In  most  edible  fruits  potash  comprises  30  to  60  per  cent,  of  the  total  ash  and  the 
absolute  amounts  shown  in  Table  39  are  very  considerable. 

Table  39. — Pounds  of  Potash  in  1,000  Pounds  of  F'resh  Fruit^^ 


Almonds 9 .  95 

Apricots 3 .  01 

Apples 1 .  40 

Bananas 6 .  80 

Cherries 2.77 

Chestnuts 3.67 

Figs 4.69 

Grapes 2.55 


Lemons 2 .  54 

Olives 9.11 

Oranges 2.11 

Peaches 3 .94 

Pears 1.34 

French  prunes 3. 10 

Plums 3.41 

Walnuts 8.18 


The  potash  content  of  seeds  is  about  the  same  as  that  of  fruits,  being  usually 
20  to  50  or  even  60  per  cent,  of  the  total  ash.^^ 

Table    40. — Potash   Content  of  Apple  Trees   of  Various  Ages 
(1  to  9  from  Thompson,^^^  13  and  100  from  Roheris,^^''  30  from  Van  Slyke^^'^) 


A 

Percentage  of  dry  weight.      B  Grams 

Leaves 

New  growth 

Trunk  and 

Roots 

Fruit 

Age 

A 

B 

A 

B 

A 

B 

A 

B 

A 

B 

1 

1.25 

0.33 

0.21 

0.20 

0.30 

0.18 

2 

1.22 

0.88 

0.34 

0.81 

0.55 

0.71 

3 

1.35 

1.22 

0.30 

2.31 

0.53 

2.39 

4 

1.13 

1.53 

0.31 

4.37 

0.48 

2.43 

5 

1.65 

7.79 

0.72 

1.56 

0.47 

16.84 

0.57 

9.34 

6 

1.00 

6.04 

0.61 

1.56 

0.35 

14.87 

0.50 

16.30 

.... 

7 

1.24 

11.64 

0.55 

2.40 

0.36 

24.45 

0.46 

18.70 

1.12 

13.87 

8 

1.42 

33.50 

0.64 

4.17 

0.31 

39.00 

0.48 

36.95 

1.20 

16.56 

9 

2.08 

75.20 

0.61 

6.76 

0.33 

80.60 

0.49 

68.40 

1.17 

39.83 

13 

1.76 

127.00 

30 

0.59 

122.00 

0.60 

9.00 

0.70 

589.00 

100 

1.43 

598. 00 

0.80 

4.00 

0.41    2697.00.  0.22 

t                1 

417.00 

.... 

150 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


In  Various  Tissues  of  Trees  of  Different  Age. — Table  40  shows  the  variations 
with  age  in  the  several  parts  of  apple  trees.  It  is  noteworthy  in  connection 
with  what  has  been  said  of  the  relations  of  potash  content  to  bearing  that  the 
30-year  old  trees  have  the  lowest  percentage  of  potash  in  the  leaves.  These  trees 
were  in  full  bearing  as  reference  to  the  last  column  of  the  table  shows.  Further- 
more, there  is  no  reduction  in  the  percentage  of  potash  in  the  leaves  of  the  100- 
year  old  tree  which  had  ceased  bearing. 

The  leaves  of  a  tree  in  full  bearing  contain  much  less  potassium  when  they 
fall  than  its  fruit.  This  is  true  of  potassium'  even  to  a  greater  degree  than  of 
phosphorus,  as  Table  41  shows. 

Table  41. — Pounds  op  Potash  in  Parts  of  a  Full  Grown  Treei'" 


Apple 

Peach 

Pear 

Plum 

Quince 

Fruit  or  fruit  pulp 

Stones 

1.28 

0.27 
0.02 

0.29 
0.01 

0.27 
0.03 

0.16 

0.09 
0.02 

0.14 
0.01 
0.01 
0.15 
0.01 

0.19 

Otems         

Leaves  

0.04 

0.01 

SULPHUR 

Data  are  not  available  to  present  a  picture  of  what  happens  to  sulphur 
in  the  fruit  tree  as  has  been  attempted  with  nitrogen,  phosphorus  and 
potash.  The  inorganic  sulphate  taken  from  the  soil  is  incorporated  into 
organic  compounds  as  both  sulphate  and  sulphide  sulphur.  As  sulphate, 
it  occurs  in  some  of  the  mustard  oils,  such  as  sinigrin;  as  sulphide,  it 
occurs  in  cystin,  one  of  the  amino-acids  used  in  the  construction  of  most 
proteins. 

Because  considerable  amounts  of  sulphur  are  lost  in  ashing,  deter- 
minations of  the  sulphur  content  of  ash  are  of  little  value.  There  are 
indications  that  plants  contain  as  much  or  more  sulpKur  than  phosphorus, 
but  satisfactory  analyses  are  yet  to  be  made. 

The  data  in  Table  42  are  representative  of  a  few  reliable  analyses  of 
sulphur  in  fruit  plants.  They  show  that  fruit  contains  approximately  as 
much  sulphur  as  phosphorus. 

Table  42. — Pounds  op  Sulphur  in  1,000  Pounds  of  Fresh  Fruits'"^ 


Apples 0.43 

Raspberries 0 .  35 

Gooseberries 0.12 

Dewberries 0.37 

Cherries 1.08 

Red  currants 0 .  56 

Blackberries 0.40 


Grapefruit   0 .  20 

Peach  pulp 0.14 

Oranges 0 .  26 

Lemons 0 .  22 

Limes 0 .  47 

Pineapple 0 .  39 


Sulphur  has  been  thought  generally  to  be  present  in  most  soils  in 
amounts  sufficient  to  meet  the  requirements  of  crop  plants  and  recent 


INDIVIDUAL  ELEMENTS  151 

investigations  would  indicate  that  this  condition  holds  for  a  great  many 
soils.  Thus  the  sulphur  content  of  Illinois  soils  has  been  reported  as 
ranging  from  280  to  750  pounds  per  acre  in  the  top  %%  inches.  ^^'^  Since 
the  average  growing  crop  removes  only  4  to  10  pounds  of  this  element  per 
acre  and  losses  through  seepage  arc  likely  to  be  nearly  offset  by  additions 
through  rainfall,  it  would  appear  that  the  application  of  sulphur  as  fer- 
tilizer to  such  soils  does  not  offer  much  promise  of  increased  crop  returns. 
However  alfalfa  removes  40  pounds  per  acre  per  year  and  cabbage  nearly 
as  much.  Moreover  there  are  many  soils  not  so  well  supplied  with 
sulphur  and  Shull^^^  is  authority  for  the  statement  that  "the  normal 
sulphur  content  of  soils  is  sufficient  for  from  15  to  70  crops,  provided 
there  are  no  additions  from  outside  sources  as  from  rainfall.  Even  if  we 
count  in  the  rainfall  sulphur,  it  is  probable  that  sulphur  is  just  as  often  a 
limiting  factor  as  is  phosphorus,  or  nitrogen,  or  potassium."  The  soils 
poor  in  sulphur  and  applications  of  compounds  containing  this  element 
of  the  Rogue  River  valley  in  southern  Oregon  have  been  found  very 
have  greatly  increased  jdelds  of  leguminous  crops.  ^^^  In  some  instances 
these  increases  have  amounted  to  500  to  1,000  per  cent.  Without  doubt 
these  conditions  are  very  exceptional;  nevertheless  the  results  suggest 
that  sulphur  may  be  a  much  more  important  Hmiting  factor  in  soil  pro- 
ductivity than  has  been  considered  generally.  Recent  investigations 
indicate  that  sulphates  have  a  special  influence  on  root  development.^^ 
This  is  particularly  marked  with  red  clover  and  rape,  where  sulphate 
applications  resulted  in  root  elongation  and  consequently  in  an  extension 
of  the  feeding  area  and  a  greater  ability  to  withstand  drought.  Little  is 
known  regarding  the  direct  effect  of  sulphur-carrying  fertilizers  on 
deciduous  fruits.  However,  the  application  of  178  pounds  of  sulphur  per 
acre  to  certain  vineyard  soils  has  resulted  in  increases  in  yield  of  19.2  to 
32.7  per  cent,  and  in  increases  of  25.03  to  27.3  per  cent,  when  applied  with 
14  tons  of  stable  manure.-^  Though  no  direct  influence  of  sulphur- 
carrying  fertilizers  upon  tree  growth  or  production  was  reported  in  the 
Rogue  River  valley  experiments  the  crops  so  greatly  benefited  by  their 
application  were  those  commonly  grown  as  intercrops  and  cover  crops  in 
the  orchard.  Through  them  the  trees  might  be  greatly  benefited  in 
later  years. 

These  facts  taken  with  the  lack  of  data  on  the  distribution  of  sulphur 
in  plants  accentuate  the  importance  of  more  analytical  and  experimental 
work  on  this  element.  Sulphur  has  been  neglected  because  it  was 
thought  to  occur  in  relatively  small  amounts,  but  the  small  amounts 
found  were  due  to  faulty  methods  of  analysis  and  sulphur  is  just  as 
essential  to  plants  and  as  worthy  of  consideration  as  phosphorus. 

IRON 

Iron  occurs  in  plants  in  even  smaller  amounts  than  sulphur.  It  is 
found  in  organic  combination  in  some  nucleic  acids.  ^"^^ 


152  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Iron  usually  constitutes  1  to  4  per  cent,  of  the  leaf  ash.  Grape  leaves  have 
been  known  to  have  an  exceptionally  high  figure,  10.20  per  cent."  The  absolute 
iron  content  of  leaves  increases  with  age,  though  the  percentage  composition  of 
the  leaf  remains  fairly  constant. 

Table  43. — Iron  Oxide  Content  of  Beech  Leaves"^ 
(In  percentage  of  total  ash) 

May  16 0.8 

July  18 1.4 

Oct.  15 1.3 

The  ash  of  bark  ranges  from  0.2  to  3  per  cent,  of  iron,  the  amount  often 
increasing  with  age;  for  example  0.2  per  cent,  has  been  found  in  the  apple  and 
2.545  per  cent,  in  the  grape.^^^  Wood  ash  has  but  little  iron,  usually  from  0.1  to 
0.8  per  cent. — 0.16  per  cent,  in  the  pear,  0.42  per  cent,  in  the  apple  and  0.635  per 
cent,  in  the  grape.*^^  Exceptionally  high  figures  have  been  found  in  the  olive, 
2.11  per  cent,  of  the  ash,  and  in  the  orange,  3.08  per  cent.*" 

Table  44. — The  Iron  Oxide  Content  of  Fruits*'*  and  Seeds^* 

(In  percentages  of  total  ash) 

Fruits  Seeds 

Banana 1 .  46     Grape 0 .  37 

Plum 2.54     Almond 0.55 

Apple 1 .  40     Walnut 1 .  32 

Pear 1.04     Coffee 0.65 

Orange 0 .  46     Chestnut 0.14 

Grape 1.04 

Olive- ..  .   0.72 

Iron  is  a  constituent  of  practically  all  soils;  furthermore  it  is  always 
found  in  quantities  sufficient  for  the  requirements  of  crop  plants.  How- 
ever, in  many  cases  it  is  held  in  the  soil  in  a  form  unavailable  to  the  plant; 
consequently  the  plants  may  suffer  because  of  iron  starvation.  Refer- 
ence has  been  made  to  this  in  connection  with  the  discussion  of  soil 
reaction  and  more  is  said  regarding  the  disturbances  caused  by  a  lack  of 
iron  under  the  heading  of  Surpluses  and  Deficiencies. 

MAGNESIUM 

The  most  important  organic  compound  containing  magnesium  is 
chlorophyll.  This  element  also  occurs  in  organic  combination  in  salts  of 
arable  acid  and  in  the  globoid  of  aleurone  grains.  Some  proteins  are 
thought  to  contain  magnesium.  Anthocyan  pigments  are  complex 
compounds  with  salts  of  magnesium,  calcium  or  other  metals. *^^ 

The  absolute  amount  of  magnesia  in  leaves  increases  as  they  grow 
older.  Thus  500  leaves  of  Platanus  were  found  to  contain  0.24  gram 
of  magnesia  on  June  13,  0.85  gram  at  the  end  of  August  and  0.69  gram 
at  leaf  fall,  showing  a  slight  decline. ^^  However,  there  is  not  much  change 
in  the  percentage  of  magnesia  in  the  total  ash.     On  May  16,  in  beech 


INDIVIDUAL  ELEMENTS 


153 


leaves  it  was  found  to  be  4.36  per  cent.;  on  July  18,  5.63  per  cent,  and 
on  Oct.  15,  4.12  per  cent.^^^  The  magnesium,  like  the  iron  content,  keeps 
pace  with  leaf  development;  this  increase  may  be  associated  with  the 
chlorophyll  content  of  the  leaf.  However,  there  is  some  evidence  that 
magnesium  is  withdrawn  to  the  branches  from  the  leaves  late  in  the 
season.  There  are  also  indications  of  magnesium  storage  in  the  sap- 
wood,  which  is  slightly  richer  in  magnesium  than  the  heart-wood.  Dur- 
ing the  spring,  there  is  more  rnagnesium  in  the  sap-wood  than  at  other 
times.  Weber  found  that  in  beeches  producing  many  seeds,  the  sap-wood 
was  especially  rich  in  magnesia  and  potash,  as  compared  with  trees 
bearing  few  seeds.  ^^^  The  sap-wood  ash  of  the  pear  has  been  found  to 
contain  3  per  cent,  magnesia,  of  the  grape  4.4  per  cent,  and  of  the  apple 
8.49  per  cent.^^ 

The  magnesia  content  of  bark  ash  decreases  with  age.  In  young 
bark  it  is  3  to  8  per  cent.,  as  in  the  leaves;  in  old  bark  2  to  5  per  cent. 
Thus  the  magnesia  of  pear  bark  has  been  found  to  be  9.4  per  cent,  of  the 
ash,  while  in  the  apple  bark  it  is  1.5  per  cent,  and  in  grape  bark  0.8 
per  cent.^^  The  sieve  tubes  sometimes  contain  magnesium  phosphate; 
this  may  be  a  form  of  storage. 

As  a  rule  fat-storing  seeds  are  richer  in  magnesia  than  starchy  or  reserve- 
cellulose  seeds;  in  the  almond,  magnesia  has  been  found  to  be  17.66  per  cent,  of 
the  ash,  in  the  walnut  13.03  per  cent.,  while  in  coffee  {Coffea  arabica)  beans  it  is 
9.69  per  cent,  and  in  chestnuts  7.47  per  cent.^^ 

Table  45  shows  that  the  leaves  of  fruit  trees  contain  much  more  magnesium 
than  the  fruit.  In  the  apple  the  magnesia  content  of  the  fruit  has  been  found  to 
be  0.10  per  cent,  of  the  dry  weight;  of  the  leaves  1.03  per  cent,  and  of  the  new 
growth  0.30  per  cent.^"> 


T.\BLE  45. — Pounds  of  Magnesia  in  Parts  of  a  Mature  Tree'®" 


Apple 

Peach 

Pear 

Plum 

Quince 

Fruit  or  pulp 

Stones 

0.18 

0.47 
0.01 

0.02 
0.01 

0.24 
0.02 

0.02 

0.06 
0.01 

0.02 

0.01 
0.07 
0.01 

0.02 

Stems 

Leaves 

N-nv  growth 

0.05 
0.01 

Table  46. — The  Magnesia  Content  of  Fruits*' 
(In  percentages  of  total  ash) 


Pineapple 9 .  79 

Banana 9.21 

Strawberry 2 .  93 

Plum 4 .  69 

Apple 8 .  75 


Pear 5 .  22 

Orange 8 .  06 

Grape 2.61 

Olive 0.18 


154 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Though  magnesium  is  necessary  for  plant  growth,  it  is  not  required 
in  large  quantities  and  so  far  as  is  known  all  soils  contain  sufficient  amounts. 
Certainly  no  data  are  available  showing  the  necessity  of  fertilizing  fruit 
plantations  with  magnesium-carrying  compounds. 


CALCIUM 

Calcium  is  for  the  most  part  absent  from  the  growing  points  and  from 
embryonic  tissues  generally  and  it  accumulates  in  all  tissues  with  age. 
This  indicates  that  calcium  is  utilized  in  ways  very  different  from  the 
other  essential  elements,  a  surmise  substantiated  by  the  fact  that  it  is  not 
necessary  for  the  growth  of  fungi. 

It  is  found  organically  combined  in  calcium  oxalate  crystals,  in 
calcium  peCtate  of  the  middle  lamella  which  holds  adjoining  cells  together, 
in  salts  of  arable  acid,  in  the  globoid  of  aleurone  grains  and  in  the  antho- 
cyan  pigments.     It  is  prevalent  also  as  calcium  carbonate. 

Seasonal  Distribution  of  Calcium. — Calcium  differs  from  the  elements 
previously  discussed  in  its  seasonal  history  in  the  tree.  It  has  been 
mentioned  that  where  potassium  is  present  in  large  amounts,  calcium 
is  usually  present  in  small  amounts  and  vice  versa. 


In  Buds  and  Leaves. — The  calcium  content  of  buds  Is  not  great  as  compared 
with  that  of  other  plant  tissues.  Leaf  buds  have  more  lime,  but  less  potassium, 
than  fruit  buds.  In  percentages  of  dry  weight,  the  Ume  content  of  leaf  buds  has 
been  found  to  be  1.364  per  cent,  in  the  cherry  and  2.365  per  cent,  in  the  plum; 
that  of  fruit  buds  was  1.113  per  cent,  in  the  cherry  and  1.761  per  cent,  in  the 
plum.i^^  Very  heavy  deposits  of  calcium  oxalate  have  been  found  in  resting 
fruit  buds,  the  amount  decreasing  after  growth  begins.  As  leaves  grow  older 
their  percentage  lime  content  increases,  as  Table  47  shows.  The  absolute  lime 
content  increases  also  (cf.  Table  48). 


Table  47. — Lime  Content  of  Leaves^^^ 
(In  percentage'  of  dry  weight) 


Apple 


Pear 


Cherry 


Plum 


May  9. 
May  14. 
May  18. 
June  22. 
Aug.  29. 
Sept.  30 
Oct.  2.. 
Oct.  15. 


1.186 


2.166 
2.762 


3.723 


0.754 


1.977 
3.147 
3.473 


1.511 

2.699 
3.987 
4.558 


1.025 
3.512 
4.591 
5.696 


INDIVIDUAL  ELEMENTS 


155 


Table  48.— Grams  of  Lime  in  100  Leaves^" 


I 

Apple 

Pear 

Cherry 

Pium 

Julv  14 

0.894 
0.966 
1.191 
1.010 

0.793 

0.396 
0.445 
0.475 
0.515 

0.335 

0.727 
0.791 
0.892 
0.939 
1.100 
0.765 

0.738 

July  31 

Aug    18,  21             

0.697 
0.699 

Sept.  3,  4,  6 

Oct.  7 

0.7.58 

Oct.  23,27,29 

Nov.  4 

0.978 

In  most  cases  there  is  a  reduction  in  the  absohite  calcium  content  before  leaf  fall, 
probably  because  of  the  dissolving  action  of  rain.  The  lime  content  of  full 
grown  leaves  is  often  very  great,  sometimes  constituting  52.82  per  cent,  of  the 
ash  of  the  olive,  54.33  per  cent,  of  the  ash  of  the  apple,  56.83  per  cent,  of  the  ash 
of  the  orange  and  34  to  60.9  per  cent,  of  the  ash  of  the  grape. ^^ 

The  data  in  Table  49  showing  the  simultaneous  changes  in  the  calcium 
content  of  leaves  and  branches  indicate  that  there  is  no  removal  of  calcium  from 
the  leaves  to  the  branches. 


Table   49. — Grams  of  Lime   in   100  Branches  of   Horse-chestnut  and  Their 

Leaves^ 


Branches 


Leaves 


July  29. 
Sept.  11 
Oct.  14. 
Nov.  16 


4.274 
6.549 
5.938 
5.804 


27.292 
39.785 
51.201 


In  Bark  and  Wood. — Young  bark  contains  considerable  lime,  about  40  per 
cent,  of  the  ash,  chiefly  in  the  form  of  calcium  carbonate.  It  increases  with  age  to 
70  or  80  per  cent,  of  the  ash,  sometimes  reaching  95  per  cent,  in  oak  bark.^^ 
Pear  bark  ash  has  been  found  to  contain  33.88  per  cent.  Ume,  apple  bark  ash 
51.84  per  cent,  and  grape  bark  ash  42.05  per  cent."  The  seasonal  variation  is 
counter  to  that  of  potassium,  there  being  proportionately  less  calcium  in  the 
bark  in  the  spring  than  at  other  times.  For  example,  in  the  walnut,  bark  ash  was 
found  to  contain  8.37  per  cent,  calcium  on  May  31  and  70.08  per  cent,  on  Aug. 
27.^^  Calcium  increases  with  age  in  the  wood  also  and  the  heart-wood  contains 
progressively  more  than  the  sap-wood,  as  Table  50  shows. 

In  general  60  to  78  per  cent,  of  wood  ash  is  lime.  In  the  orange  it  has  been 
known  to  rise  to  68.88  per  cent.^^  In  the  sap-wood  there  is  less;  in  the  pear 
there  has  been  found  27.39  per  cent.,  in  the  apple  18.65  per  cent,  and  in  the  grape 
25.67  per  cent.^'*  In  the  heart-wood,  the  vessels  and  sometimes  the  tracheids, 
wood  fibers  and  parenchyma  cells  are  filled  with  spherites  of  calcium  carbonate. 
The  older  the  wood,  the  more  calcium  there  is  in  its  ash. 


156 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Table  50. — Ash  Content  of  He  art- wood  in  a  Red  Beech  ^o* 
(In  percentages  of  dry  weight) 


Rings 

Ash 

CaCOs 

Ito  15 

1.162 

0.579 

15  to  25 

0.825 

0.251 

25  to  35 

0.645 

Trace 

35  to  45 

0.612 

Trace 

45  to  60 

0.555 

60  to  83 

0.458 

83  to  94  (sap-wood) 

0.205 

/?t  Fruits. — In  fruit  trees,  the  calcium  required  by  the  crop  is  insignificant 
compared  with  that  lost  with  the  leaves  and  sometimes  it  is  less  than  that  in 
the  new  growth.     This  is  shown  in  Table  51.     In  one  set  of  determinations  the 

Table  51. — Pounds  of  Lime  in  Parts  of  a  Full  Grown  TreeI'"' 


Apple 

Peach 

Pear 

Plum 

Quince 

Fruit  or  fruit  pulp 

Stones 

Stems..' 

Leaves 

New  growth 

0.12 

1.42 
0.08 

0.02 
0.00 

0.79 
0.14 

0.03 

.... 
0.25 
0.04 

0.01 
0.00 
0.02 
0.22 
0.09 

0.01 

0.19 
0  07 

lime  in  apple  leaves  was  3.10  per  cent,  of  their  dry  weight;  in  new  growth  2.39 
per  cent,  and  in  the  fruit  0.06  per  cent.'*"  However,  the  lime  content  of  fruits 
is  not  inconsiderable  (see  Table  52). 


Table  52. — Pounds  of  Lime  in  1,000  Pounds  of  Fresh  Fruit  ^^ 


Almonds . 


1 .  04     Lemons 1 .  55 


Apricots 0.16 

Apples 0.11 

Bananas 0.10 

Cherries 0 .  20 

Chestnuts 1 .  20 

Figs 0.85 

Grapes 0 .  25 


Olives 2.43 

Oranges 0 .  97 

Peaches 0.14 

Pears 0.19 

French  prunes 0 .  22 

Plums 0.25 

Walnuts 1 .  55 


According  to  Trabut,  "a  high  lime  content  is  a  very  favorable  factor  in  grow- 
ing olives  for  oil  production,  as  olives  produced  in  limestone  regions  are  richer  in 
oil  and  the  oil  is  of  better  quality  than  where  the  soils  are  deficient  in 
this  component.  "^"^ 

The  Demand  and  the  Supply. — In  general  it  may  be  said  that  the 
calcium  requirements  of  fruit  trees  are  insignificant  compared  with  the 
amounts  usually  available  in  the  soil.  For  instance,  it  has  been  shown 
that  certain  typical  Illinois  soils  contain  quantities  sufficient  in  the  sur- 


INDIVIDUAL  ELEMENTS  157 

face  layers  to  produce  5,000  to  55,000  heavy  corn  crops  if  the  supply  is  not 
replenished  and  if  it  becomes  available  gradually.  ^'^^  All  the  chemical 
analyses  of  fruit  soils  given  in  the  chapter  on  Orchard  Soils  indicate  that 
the  danger  from  calcium  starvation  in  the  orchard  is  very  remote.  In 
all  probabihty  the  amounts  of  calcium  found  in  plant  tissues  are  often 
much  in  excess  of  their  nutritive  requirements.  There  is  no  doubt  that 
calcium  is  of  use  in  the  elimination  of  poisonous  products  of  catabolism, 
such  as  oxalic  acid,  but  it  seems  not  at  all  unlikely  that  in  many  cases  the 
oxalic  acid  is  produced  as  a  means  of  rendering  a  surplus  of  calcium 
insoluble. 

Many  orchard  fertilizer  experiments  have  been  conducted  in  which 
lime  has  been  used,  either  alone  or  in  combination.  The  results  attending 
these  experiments  have  been  variable,  but  on  the  whole  negative  in 
character.  Certainly  there  is  no  clear  evidence  available  to  show  that 
liming  the  soil  is  of  any  direct  benefit  to  the  trees.  It  has  been  pointed 
out  that  applications  of  lime  may  aid  nitrification  in  the  soil  and  may  be 
of  use  to  other  cultures  that  are  being  grown  in  the  fruit  plantation  and 
thus  -indirectly  to  the  trees;  on  the  other  hand,  it  has  been  shown  also 
that  they  may  have  a  very  deleterious  influence  on  tree  or  vine  growth  and 
these  deleterious  influences  are  of  sufficiently  frequent  occurrence  in 
actual  field  practice  to  suggest  caution.  It  may  be  recalled  that  the 
purpose  for  which  lime  is  generally  used  with  field  crops,  namely  the 
correction  of  soil  acidity,  needs  but  little  consideration  in  deciduous  fruit 
production. 

OTHER  MINERAL  ELEMENTS 

Beside  the  elements  already  discussed,  there  are  others  that  are  of 
universal  occurrence  in  plants,  though  they  are  generally  considered  to  be 
unessential.  However,  copper  which  occurs  in  very  small  amounts 
in  plant  tissues  is  considered  by  Maquenne  and  Demoussey''^  to  be  an 
essential  element. 

Silicon. — Silica  is  universally  present,  though  the  amount  is  very  variable. 
In  leaves,  for  example,  it  may  be  present  in  mere  traces  or  it  may  constitute  80 
per  cent,  of  the  ash.  In  grape  leaves  amounts  ranging  from  1.61  per  cent,  to 
39.44  per  cent,  have  been  found,  the  amount  usually  increasing  with  age.** 
Table  53  illustrates  this  point. 

T.VBLE  53. — Grams  of  Silica  in   100  Branches  of  Horse-chestnut  and  Their 

Leaves  ^ 


Branches 

Leaves 

July  29 

0.095 
0.165 
0.084 
0.056 

14.187 

Sept.  11 

18  812 

Oct.  14 

Nov.  16 

18.195 

158  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Bark  ash  usually  contains  less  than  2  per  cent,  of  sihca;  for  example,  0.4  per 
cent,  in  the  pear  and  0.6  per  cent,  in  the  apple. ^*  The  ash  of  grape  bark  has  been 
shown  to  contain  14.3  per  cent.  siUca.^  Wood  ash  usually  contains  less  than 
3  per  cent,  of  silica;  for  example,  0.3  per  cent,  has  been  recorded  for  pear  wood, 
1.65  per  cent,  for  apple  wood  and  2.8  per  cent,  for  grape  wood.^''  The  ash 
of  olive  wood  has  been  found  to  contain  as  much  as  14.23  per  cent,  silica. ^^  As  a 
rule  the  heart- wood  contains  a  higher  percentage  than  the  sap-wood. 

Fruits  contain  silica  in  amounts  shown  in  Table  54.  The  seed  usually  con- 
tains less,  as  the  same  table  shows,  though  a  trace  at  least  is  always  present. 

Table  54. — The  Silica  Content  of  Fruits^''  and  Seeds" 

(In  percentages  of  total  ash) 

Fruits  Seeds 

Pineapple 5 .  77     Chestnut 1 .  54 

Banana 5.93     Grape 1 .  04 

Fig 2.34     Coffee 0.54 

Plum 3.15     Cocoanut 0 .  50 

Apple 4.32     Walnut Trace 

Pear 1.49 

Orange 0 .  44 

Grape 1 .  00 

Olive 0.65 

SiUcon  usually  is  associated  with  the  cell  wall  and  sometimes  confers  strength 
and  stability  on  a  plant  tissue.  However,  the  strongest  and  hardest  of  plant 
materials  are  often  of  very  nearly  pure  cellulose ;  hence,  a  lack  of  silicon  does  not 
necessarily  involve  mechanical  weakness  of  mature  tissues. 

Sodium. — Sodium  also  is  of  universal  occurrence  in  plant  tissues.  Leaves 
usually  contain  1  to  3  per  cent.  Table  55  indicates  the  seasonal  variation  in 
absolute  amounts  in  five  hundred  Plalanus  leaves. 

Table  55. — The  Seasonal  Variation  in  Soda  Content  of  Platanus  Leaves" 
(Grams    in    500    leaves) 

June  13 0.3152     Oct.  8 0.2898 

May  15 0.4187     Oct.  24 0.2439 

Aug.  22 0.4299     Nov.  5 0.2273 

Sept.  7 0.5641 

Bark  and  wood  ash  usually  contain  but  little  soda,  3.495  per  cent,  having  been 
recorded  in  the  ash  of  apple  bark  and  0.27  per  cent,  in  that  of  grape  bark.^^  The 
wood  of  the  sweet  cherry  has  been  known  to  contain  as  much  as  10.13  per  cent.^® 
As  a  rule  there  is  less  soda  in  the  ash  of  heart-wood  than  in  that  of  sap-wood, 
certain  sap-wood  records  showing  for  the  pear  1.84  per  cent,  soda;  for  the  apple, 
3.275  per  cent,  and  for  the  grape,  2.06  per  cent.«^  Fruits  contain  soda  in  the 
widely  varying  amounts  shown  in  Table  56. 

Table  56. — The  Soda  Content  of  Fruits  ^^ 
(In  percentages  of  total  ash) 

Pineapple 6.75     Apple 26.09 

Banana 26.27     Pear 8.52 

Fig 19.63     Orange 13.47 

Plum 9.05     Olive 7.53 


INDIVIDUAL  ELEMENTS  159 

Seeds  usually  contain  less  than  fruits,  from  1  to  2  per  cent.,  but  walnuts  have 
been  recorded  as  having  2.25  ])er  cent.,  cocoanuts  8.39  per  cent,  and  dates  9.03 
per  cent.^' 

Though  sodium  is  regarded  as  unessential  for  the  growth  of  very  many 
plants,  investigations  with  turnips,  radishes,  beets,  cucumbers,  buckwheat, 
oats,  potatoes  and  a  number  of  other  crop  plants,  indicate  that  this 
element  can  partially  replace  potassium  when  the  latter  is  not  present  in 
amounts  sufficient  for  good  growth. ^^  "In  the  field,  however,  more 
potassium  was  removed  in  the  larger  crops  which  usually  resulted  when 
sodium  was  increased  in  connection  with  an  insufficient  amount  of 
potassium,  and  this  was  in  spite  of  the  fact  that  sodium  frequently  de- 
creased the  percentage  of  potassium  in  the  crop.  A  portion  of  the  bene- 
fits arising  from  the  use  of  sodium  in  the  field  is,  therefore,  attributable  to 
indirect  action,  but  the  solution  work  indicates  that  also  direct  beneficial 
effects  were  probably  obtained  in  the  field. "^^ 

Probably  this  function  of  sodium  is  of  little  direct  importance  in  the 
deciduous  fruit  plantation,  since  it  is  very  seldom  that  a  lack  of  potassium 
is  a  limiting  factor;  however,  it  is  at  least  a  matter  of  interest. 

Chlorine. — Chlorine  occurs  in  many  plants,  but  seldom  in  large  amounts  except 
in  salt  marsh  plants.  In  leaves  the  amount  varies  from  25  per  cent,  of  the  total 
ash  to  mere  traces.  The  chlorine  content  of  bark  ash  is  low,  certain  records  in 
the  pear  showing  1.7  per  cent.,  in  the  apple  0.33  per  cent,  and  in  the  grape  0.4 
per  cent.^  The  chlorine  content  of  wood  ash  is  even  less,  being  0.31  per  cent,  in 
the  pear,  0.255  per  cent,  in  the  apple  and  0.02  per  cent,  in  the  grape. ^"^  The 
chlorine  content  of  fruits  is  more  variable,  but  never  very  great. 

Table  57. — The  Chlorine  Content  of  Fruits" 
(In   percentages   of   total   ash) 

Pineapple Trace     Plum 0 .  38 

Banana 2.69     Orange 2.35 

Fig 0.83     Olive 0.16 

Seeds  usually  have  0.5  to  1.5  per  cent,  of  chlorine  in  the  ash,  but  the  amount 
present  varies  greatly.  Walnuts  and  almonds  have  mere  traces.  Other  records 
are:  for  chestnuts,  0.52  per  cent,  of  the  ash,  for  grape  seeds,  0.27  per  cent,  and  for 
the  cocoanut,  which  grows  on  the  sea-shore,  13.42  per  cent.^'* 

There  is  no  definite  relation  between  the  amount  of  sodium  and  the  amount 
of  chlorine  a  tissue  contains. 

It  would  appear  from  the  preceding  statements  that  no  benefit  would 
be  derived  from  the  chlorine  in  fertilizers  carrying  this  element.  Com- 
mon salt  has  often  been  suggested  as  having  possible  value  as  a  fertilizer 
and  has  been  tried  in  a  limited  way.  So  far  as  records  are  available  they 
indicate  that  it  is  of  no  value  for  deciduous  or  for  most  other  fruit  trees. 
However,  greatly  increased  yields  of  the  mango  have  been  reported  in  the 
province  of  Bombay,  India,  from  applying  10  pounds  to  the  tree  and 


160  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

likewise  marked  increases  in  yield  from  its  application  to  cocoanuts.'^^ 
To  what  extent  these  increases  were  due  to  direct  or  indirect  effects  of  the 
sodium  Or  the  direct  or  indirect  effects  of  the  chlorine  is  not  known. 

Alumintun  and  Manganese. — Manganese  is  a  common  constituent  of  the 
bark,  where  it  seldom  exceeds  1  per  cent,  of  the  ash.  The  other  parts  of  the 
tree  usually  have  less  than  the  bark.  Aluminum  and  manganese  combined 
average  0.5  to  0.9  per  cent,  of  wood  ash.  Aluminum  is  not  uncommon  in  seeds. 
It  sometimes  comprises  0.062  per  cent,  of  the  ash  of  fig  seeds  and  0.138  per  cent, 
of  the  ash  of  almonds.'*^  Aluminum  is  capable  of  forming  complex  salts  with 
the  anthocyan  pigments."  The  color  of  the  pigment  depends  on  the  base  which 
it  contains,  which  accounts  for  the  fact  that  the  hydrangea  {H.  hortensis)  develops 
blue  instead  of  pink  flowers  when  soluble  aluminum  compounds  are  applied  to 
the  soil  in  which  it  grows.  "^ 

Summary. — Certain  elements,  especially  nitrogen,  phosphorus,  potas- 
sium and  sulphur  are  present  in  greatest  amount  in  young  tissues.  Cer- 
tain amounts  are  stored  in  the  bark  over  the  winter  and  in  the  spring  a 
supply  is  on  hand  for  the  rapid  development  of  leaves  and  shoots,  flowers, 
fruit  and  seeds.  Since  the  seeds  themselves  are  storage  organs  and  in  addi- 
tion contain  embryonic  tissue,  they  accumulate  these  elements  in  relatively 
large  proportions.  Magnesium  and  iron  likewise  are  stored  in  the  bark 
and  in  the  wood  as  well.  They  are  utihzed  in  new  growth,  though  they 
appear  to  be  more  equally  distributed  in  mature  and  in  embryonic 
tissues.  All  of  these  elements  show  more  or  less  mobility  and  are  trans- 
located to  regions  where  they  are  more  in  demand.  The  plant  con- 
serves its  supply  and  withdraws  at  least  a  part  of  the  amount  contained 
in  the  leaves,  after  they  have  ceased  to  function. 

Calcium  and  silicon  are  very  nearly  absent  from  embryonic  tissues. 
They  accumulate  throughout  the  plant  with  age.  There  are  no  indica- 
tions that  these  elements  are  stored  for  future  use  and  to  a  great  degree 
they  remain  where  they  are  deposited. 

With  respect  to  the  other  mineral  elements  found  in  plants,  little 
can  be  said  in  generalization.  This  is  because  no  regularity  has  been 
observed  in  the  amounts  present  or  in  their  seasonal  variation. 


CHAPTER  IX 

MANUFACTURE  AND  UTILIZATION  OF  CARBOHYDRATES 

.  The  essential  elements  discussed  in  the  previous  section  are  used 
ultimately  in  the  construction  of  the  plant's  substance.  They  are  indis- 
pensible  because  the  plant  cannot  be  constructed  unless  each  one  of 
them  is  present. 

ASSIMILATION  AND  LIMITING  FACTORS  DEFINED 

The  term  assimilation,  in  its  broadest  sense,  is  used  to  describe  the 
process  by  which  a  plant  builds  up  the  substances  that  comprise  it  out  of 
compounds  obtained  from  its  environment.  To  be  sure  any  compound 
will  not  serve;  certain  specific  materials  are  necessary.  Assimilation 
depends  on  a  supply  of  such  materials  and  on  a  source  of  energy.  The 
amount  of  assimilation  and  hence  of  growth  is  determined  by  the  opera- 
tion of  the  principle  of  limiting  factors. 

Most  plants  require  at  least  seven  elements  in  combined  form  from 
the  soil,  namely,  S,  P,  N,  K,  Fe,  Mg  and  Ca.  If  «S,  )8P,  7N,  5K, 
eFe,  rMg  and  7?Ca  combine  exactly  to  produce  a  unit  amount  of  growth 
in  some  particular  plant,  say  an  apple  tree,  and  if  aS,  6P,  cN,  dK,  eFe, 
/Mg  and  gCa  are  present  in  a  particular  soil  in  available  form,  the  maxi- 
mum amount  of  apple  tree  tissue  that  can  be  grown  in  that  soil  will  be 
the  smallest  of  the  fractions  a/a,  h/^,  c/y,  d/8,  e/e,  //f,  g/rj.  That 
element  which  gives  the  smallest  fraction  is  the  limiting  factor  of  growth.®^ 

The  principle  of  limiting  factors  applies  not  merely  to  nitrogen  and  the 
essential  mineral  elements,  but  also  to  water,  to  carbon  dioxide  and  to 
oxygen  which  likewise  are  essential  nutrients  entering  into  the  composi- 
tion of  the  plant.  Moreover  the  principle  covers  the  effects  of  external 
factors  such  as  temperature  and  light  which  also  may  be  limiting  factors 
of  assimilation.  All  of  these  possible  limiting  factors  of  assimilation 
and  growth  constitute  the  external  stimuli  to  which  the  organism  reacts 
and  these  reactions  tend  to  overcome  the  limiting  factors  of  assimilation 
and  so  bring  the  organism  in  the  most  favorable  situation  for  assimila- 
tion that  circumstances  permit.  In  consequence  of  the  reactivity  of 
the  plant  and  its  apparent  complete  adjustment  to  its  environment 
the  principle  of  limiting  factors  sometimes  may  seem  not  to  be  operative. 
This,  however,  is  not  the  case,  for  the  principle  of  limiting  factors  is 
always  effective.  The  principle  is  generally  recognized  in  the  saying 
that  a  chain  is^no  strenger  than  its  weakest  link  and  it  is  so  universally 
11  161 


162  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

applied  in  everyday  life  that  it  is  taken  as  a  matter   of   course    and 
consequently  overlooked. 

The  principle  of  limiting  factors  is  particularly  important  for  an 
understanding  of  the  process  of  carbon  assimilation  and  it  has  a  direct 
practical  application  in  the  use  of  fertihzers.  These  two  subjects  are 
discussed  in  the  following  pages. 

CARBON  ASSIMILATION 

The  synthesis  of  organic  compounds  in  plants  depends  on  the  assimi- 
lation of  an  element  which  occurs  in  and  is  characteristic  of  all  organic 
compounds,  namely,  carbon.  This  element  is  provided  by  the  carbon 
dioxide  of  the  air,  which,  together  with  water  absorbed  by  the  roots, 
furnishes  the  materials  for  the  synthesis  of  carbohydrates.  These 
compounds  contain  more  potential  energy  than  those  from  which  they 
are  formed;  this  energy  is  supplied  by  the  sun,  whose  radiant  energy  is 
transformed  into  the  potential  energy  of  carbohydrates  by  means  of  the 
green  pigments  of  the  leaf,  the  chlorophylls.  The  reaction  or  reactions 
by  which  water  and  carbon  dioxide  in  the  presence  of  light  and  through 
the  agency  of  chlorophyll  form  carbohydrates  and  oxygen  depend  on  two 
other  factors,  namely,  enzymes  and  temperature  which  affects  the  rate  of 
all  chemical  reactions. 

Factors  Involved 

The  rate  of  carbon  assimilation  depends  on  six  factors: 

1.  The  supply  of  carbon  dioxide. 

2.  The  supply  of  water. 

3.  The  intensity,  duration  and  quality  of  light. 

4.  The  amount  of  chlorophyll. 

5.  Temperature. 

6.  The  amount  of  enzymes. 

Carbon  Dioxide. — The  carbon  dioxide  content  of  the  atmosphere  is 
practically  constant,  varying  little  from  3  parts  in  each  10,000  of  air. 
Carbon  dioxide  enters  the  leaf  mainly  through  the  stomata,  though  the 
epidermis  with  its  cuticle  is  slightly  permeable  to  it.  Hence  the  diffu- 
sion of  carbon  dioxide  into  the  leaf  depends  on  about  the  same  factors  as 
the  outward  passage  of  water  vapor,  namely,  the  number  of  stomata,  the 
rate  at  which  carbon  dioxide  is  utilized  within  the  leaf  and  the  condition 
of  the  air  outside  the  leaf,  whether  it  be  moving  or  still. 

The  amount  of  carbon  dioxide  assimilated  has  been  shown  to  depend 
on  the  number  of  stomata  on  the  upper  and  the  lower  surfaces  of  the  leaf. 
For  example,  Table  58  shows  the  relation  in  leaves  illuminated  on  the 
upper  surface.  In  leaves  with  stomata  confined  to  one  surface  the  cor- 
relation of  assimilation  to  number  of  stomata  holds,  but  with  leaves 
bearing  stomata  on  both  surfaces  there  is  more  intake  of  carbon  dioxide 


MANUFACTURE  AND  UTILIZATION  OF  CARBOHYDRATES      163 


Table  58. — The  Relation  of  Carbon  Dioxide  Assimilated  to  the  Number  of 

Stomata  in  Leaves  Illuminated  on  the  Upper  Surface 

{After  Brown  and  Escomhe--) 


Stomatal  ratio 
Upper  surface 
Lower  surface^ 

CO2  assimilated 
Upper  surface 
Lower  surface 

100 

0 

0 

100 
100 
119 
100 
269 

100 

Catalpa  hignonioides 

Colchiciini  speciosum 

0 

0 

100 
100 

Rutncx  (ilpitius .              

72 
100 

144 

than  might  be  expected  from  the  number  of  stomata  on  the  upper  side. 
This  is  because  the  leaves  were  ilhmiinated  from  above,  resulting  prob- 
ably in  a  greater  degree  of  opening  of  the  stomata  and  a  more  rapid 
utilization  of  carbon  dioxide  by  this  side  of  the  leaf.  Both  of  these 
factors  would  favor  a  more  rapid  intake  of  carbon  dioxide. 

The  large  amount  absorbed  by  a  leaf  during  active  assimilation 
despite  the  low  partial  pressure  of  carbon  dioxide  in  the  atmosphere  and 
the  small  fraction  of  the  leaf  surface  occupied  by  stomata  is  explained 
by  Brown  and  Escombe's  law"^  which  states  that  diffusion  through  a 
perforated  membrane  is  proportional  to  the  diameter  of  the  apertures  and 
not  to  their  area.  Because  of  the  small  size  of  the  stomata,  their  great 
number  and  their  distribution  over  the  surface,  the  amount  of  carbon 
dioxide  that  theoretically  could  be  taken  in  by  the  leaf  under  the  most 
favorable  circumstances  is  much  greater  than  any  observed  quantity 
absorbed.  Some  idea  of  the  amount  used  by  leaves  is  given  by  an  experi- 
ment of  Brown  and  Escombe^^  on  the  sunflower,  in  which  they  found 
that  approximately  half  a  liter  of  carbon  dioxide  was  used  by  each  square 
meter  of  leaf  surface  in  an  hour. 

The  carbon  dioxide  content  of  the  atmosphere  is  constant;  therefore 
it  is  not  a  factor  to  be  considered  in  fruit  growing.  However,  when  it 
is  artificially  changed,  in  the  absence  of  other  limiting  factors,  the  rate 
of  assimilation  increases  in  proportion  to  an  increase  in  the  carbon  dioxide 
supply  until  an  atmospheric  concentration  of  30  to  50  per  cent,  is  reached. 
Cummings  and  Jones^"  have  obtained  very  marked  results  from  aerial 
fertilization  with  carbon  dioxide.  Legumes  fertilized  in  this  way  showed 
increased  carbohydrate  storage  and  an  increased  production  of  pods 
and  beans.  Potatoes  produced  better  tubers  and  strawberries  showed 
distinct  effects.  This  probably  holds  until  an  atmospheric  concentration 
of  about  30  per  cent,  or  more  is  reached.     Atmospheric  concentrations 


164  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

of  50  per  cent,  carbon  dioxide  have  a  narcotic  effect  and  depress  assimi- 
lation. Changes  in  the  rate  of  assimilation  in  so  far  as  they  depend  on 
carbon  dioxide  supply  are  affected  only  by  those  factors  that  determine  the 
rate  of  intake.  This  is  increased  by  movement  of  the  air,  by  the  degree 
of  stomatal  opening  and  by  any  factors  increasing  the  rate  of  utilization. 

Water. — The  water  supply  of  plants  is  treated  in  a  preceding  section 
and  no  further  discussion  need  be  added  here.  However,  it  must  not  be 
forgotten  that  water  is  one  of  the  materials  out  of  which  carbohydrates 
are  made. 

Light. — In  the  absence  of  limiting  factors  and  particularly  of  high 
temperatures  and  extremely  high  light  intensities,  carbon  assimilation 
increases  with  the  intensity  of  light.  Under  such  circumstances  equal 
areas  of  different  plants,  equally  illuminated,  produce  the  same  amounts 
of  carbohydrates.  There  is  evidence  that  at  the  intensities  of  the  different 
wave  lengths  in  the  solar  spectrum,  red  light  is  the  most  and  green  the 
least  effective  for  photosynthesis. 

Light  acts  indirectly  on  carbon  assimilation  by  raising  the  tempera- 
ture of  the  leaf  and  by  stimulating  the  guard  cells  of  the  stomata  to 
open,  thus  increasing  the  absorption  of  carbon  dioxide. ^^ 

Leaf  Pigments. — The  chloroplasts  of  all  green  plants  contain  four 
pigments,  two  green  and  two  yellow.     They  are: 

L  Chlorophyll  a,  blue-black  in  the  solid  state,  green-blue  in  solution. 

2.  Chlorophyll  b,  green-black  in  the  solid  state,  pure  green  in 
solution. 

3.  Carotin,  forming  orange-red  crystals. 

4.  Xanthophyll,  forming  yellow  crystals. 

In  the  fresh  nettle  leaf,  these  four  pigments  occur  in  the  following 
quantities,  chlorophyll  a,  24  parts  in  12,000;  chlorophyll  b,  9;  carotin  2 
and  xanthophyll  4.'"=' 

In  the  chloroplast  these  pigments  occur  in  a  colloidal  mixture  with  fats, 
waxes  and  salts  of  fatty  acids.  The  chlorophyll  content  of  leaves  varies  from  9.6 
to  1.2  per  cent,  of  the  dry  weight.  Shade  leaves  have  a  higher  chlorophyll 
content  than  sun  leaves  in  terms  of  dry  weight,  but  not  in  proportion  to  leaf 
surface.  The  yellow  pigments  comprise  0.1  to  1.2  per  cent,  of  the  dry  weight  and 
there  is  no  higher  percentage  in  shade  leaves  than  in  sun  leaves.  There  is  no 
diurnal  fluctuation  in  the  amounts  of  the  pigments,  the  mean  ratio  of  chloro- 
phyll a  to  chlorophyll  b  being  2.85:1.  On  the  whole,  shade  leaves  con- 
tain less  chlorophyll  a  than  other  leaves,  their  ratio  of  chloroph.ylls  being 
2.93:1.  Less  difference  in  this  ratio  is  found  in  real  shade  plants  like  the  beech 
than  in  plants  that  are  ill  adapted  to  growth  in  the  shade.  The  mean  ratio  of 
carotin  to  xanthophyll  for  ordinary  leaves  is  0.603  : 1  and  for  shade  leaves 
0.421  : 1.     Xanthophyll  is  relatively  more  abundant  in  shade  leaves. 

Variation  with  Age. — The  chlorophyll  content  of  leaves  increases 
with  age;  so  also  the  assimilatory  power  of  the  leaf,  though  not  in  the 


MANUFACTURE  AND  UTILIZATION  OF  CARBOHYDRATES      165 

same  degree.  Hence,  it  appears  that  mature  leaves  contain  an  excess 
of  chlorophyll  and  some  other  factor  limits  the  rate  of  assimilation. 
In  autumn  the  chlorophyll  content  decreases  but  as  chlorophyll  is  not 
usually  the  limiting  factor,  assimilation  does  not  decrease  in  proportion 
at  first.  If  leaves  remain  green,  they  maintain  their  assimilatory  power 
until  they  fall — a  matter  of  no  small  importance  in  food  storage. 

Variation  with  Light  Supply. — The  development  of  chlorophyll  in  most 
plants  depends  on  the  action  of  light  in  which  the  red  rays  seem  the  most  effect- 
ive.", 189  In  all  probabiUty  precursors  of  chlorophyll  are  present  and  exposure 
to  light  effects  certain  chemical  reactions  necessary  for  the  complete  development 
of  the  pigment.  Light  is  not  always  essential  to  chlorophyll  development,  how- 
ever, for  conifer  seeds  germinate  and  become  green  even  in  the  dark. 

Light  not  only  aids  in  the  development  of  chlorophjdl  but  at  higher  intensities 
brings  about  its  destruction  probably  through  oxidation.  The  decomposition  of 
chlorophyll  occurs  outside  the  plant  as  well  as  within  its  tissues.  This  can  be 
demonstrated  by  exposing  a  test  tube  containing  a  solution  of  chlorophyll  to 
the  light  and  comparing  it  with  another  kept  in  darkness.  Red  and  yellow 
light  are  most  effective  in  destroying  chlorophyll.  Consequently  it  is  found 
that  at  low  light  intensities  plants  grown  in  yellow  light  contain  the  most  chloro- 
phyll but  that  at  higher  intensities  plants  grown  in  blue  hght  contain  the  most, 
owing  to  the  destructive  effect  of  the  yellow  light  at  these  higher  intensities.^"^ 
Similar  effects  from  red  light  have  been  observed.  !*■*  The  double  effect  of  Hght 
in  stimulating  the  development  of  chlorophyll  and  in  bringing  about  its  destruc- 
tion, leads  to  noticeable  differences  in  the  chlorophyll  content  of  plants  growing 
in  different  latitudes  and  altitudes.  It  has  been  found  that  the  minimum  amount 
of  chlorophyll  necessary  for  growth  is  approximately  the  same  at  all  latitudes 
but  that  the  maximum  amount  increases  toward  the  equator.  ^^"^  Hence,  a 
plant  may  have  twice  as  much  chlorophyll  in  the  tropics  as  at  60°  north  latitude. 
For  a  given  species,  however,  the  amount  is  less  at  both  extremes  of  its  range 
than  at  the  center  and  it  has  been  suggested  that  this  may  be  due  to  greater 
oxidizing  action  at  the  limit  on  the  equator  side  where  the  light  would  be  more 
intense.  The  significance  of  these  discoveries  lies  in  the  relation  of  carbohydrate 
accumulation  to  fruitfulness.  Plants  growing  at  high  altitudes  contain  less 
chlorophyll  than  those  growing  in  the  lowlands. ^^  In  Alpine  plants  carbon  assimi- 
lation requires  greater  light  intensities  but  lower  temperatures. 

Temperature. — At  low  and  medium  temperatures  in  the  absence  of 
other  limiting  factors,  the  rate  of  assimilation  is  a  coefficient  of  the  tem- 
perature. Assimilation  has  been  detected  at  —  6°C.  and  from  this  point 
to  25°C.  the  rule  stated  above  has  been  found  to  hold  with  the  plants 
investigated.  Above  25°C.,  the  rate  of  assimilation  does  not  remain 
constant  at  any  given  temperature.  The  higher  the  temperature,  the 
more  rapidly  it  decreases;  at  any  given  temperature  the  initial  decrease 
is  greatest.  This  "time  factor"  that  enters  at  higher  temperatures 
probably  is  indicative  of  the  interference  of  another  factor,  namely, 
enzymes. 


166  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Enzymes. — Assimilation  is  an  enzyme  reaction.  Enzymes  are 
organic  catalytic  substances  that  accelerate  the  rate  of  a  reaction.  Their 
chemical  composition  is  unknown  and  their  existence  is  shown  only 
by  their  activity.  They  are  not  used  up  in  a  reaction,  remaining  after 
the  process  is  completed.  A  minute  amount  of  enzyme  can  effect  the 
formation  of  a  relatively  large  amount  of  end  product;  however,  this 
is  proportional  to  the  amount  of  enzyme  present.  The  effects  of  tem- 
perature described  above  are  characteristic  of  enzyme  reactions.  The 
time  factor  manifesting  itself  at  temperatures  above  25°C.  is  not  due 
to  any  direct  effect  of  the  temperatures  on  assimilation,  but  may  be 
due  to  the  permanent  inactivation  or  decomposition  of  enzymes  at 
high  temperatures.  Under  these  circumstances  the  rate  of  assimilation 
would  decrease  because  the  amount  of  enzyme  diminished.  The  longer 
the  temperature  acted,  the  more  enzyme  would  be  decomposed.  Simi- 
larly the  narcotic  effect  of  strong  concentrations  of  carbon  dioxide  and 
the  harmful  influences  of  high  light  intensities  are  attributable  in  part 
to  their  effects  on  the  assimilatory  enzymes.  Such  adaptations  as 
different  species  may  show  in  their  ability  to  assimilate  best  at  higher 
or  lower  temperatures  or  light  intensities  probably  are  attributable  to 
differences  in  their  enzymes. 

The  principle  of  limiting  factors  applies  to  the  six  factors  determining 
carbon  assimilation.^^  If  any  one  factor  is  limiting,  the  rate  of  assimila- 
tion cannot  be  increased  by  any  other.  The  carbon  assimilation  of  green 
plants  is  usually  limited  by  the  seasonal  variation  in  temperature  and  the 
diurnal  variation  in  light.  When  temperature  and  light  are  both  favor- 
able, the  supply  of  carbon  dioxide  is  probably  the  limiting  factor.^^ 
Water  may  be  a  limiting  factor  either  through  a  direct  effect  on  assimila- 
tion or  indirectly  by  closing  the  stomata  and  so  shutting  off  the  supply 
of  carbon  dioxide. 

Products 

The  products  of  photosynthesis  are  oxygen  and  carbohydrates. 

Oxygen. — The  relation  between  the  amount  of  oxygen  evolved  in  the 
process  of  carbon  assimilation  and  the  amount  of  carbon  dioxide  taken  in 
is  not  accurately  known.  When  the  respiration  of  the  assimilating 
tissue  is  evaluated,  it  appears  that  the  volume  of  oxygen  evolved  is  prac- 
tically equal  to,  or  very  slightly  greater  than,  the  amount  of  carbon  dioxide 
absorbed.  The  path  by  which  oxygen  escapes  from  the  leaf  is  the  same  as 
that  by  which  carbon  dioxide  enters  or  water  vapor  is  lost,  namely, 
through  the  intercellular  spaces  and  the  stomata.  Oxygen  is  used  in 
respiration,  however,  and  when  assimilation  proceeds  very  slowl}^,  the 
oxygen  given  off  by  assimilation  may  be  entirely  consumed  by  respiration. 
Similarly  the  carbon  dioxide  evolved  by  respiration  may  just  about  equal 
that  used  in  assimilation  under  these  circumstances. 


MANUFACTURE  AND  UTILIZATION  OF  CARBOHYDRATES      167 

Carbohydrates. — What  carbohydrate  is  the  first  product  of  carbon 
assimilation,  is  not  known.  Assuming  it  to  be  glucose,  the  reaction  may 
be  written  as  follows:  6CO2  +  6H2O  +  light  +  chlorophyll  =  CeHiaOe 
+  6O0. 

Simple,  naturally  occurring  carbohydrates  may  contain  five  or  six 
carbon  atoms  and  are  called  accordingly  pentoses  or  hexoses.  There  are 
two  pentoses  of  common  occurrence,  arabinose  and  xylose;  neither  of  these 
has  been  shown  to  be  formed  directly  by  assimilation.  Four  naturally 
occurring  hexoses  are  known:  glucose,  fructose,  mannose  and  galactose. 

Besides  these  simple  sugars,  there  are  compound  sugars  made  up  of 
two  or  more  molecules  of  the  simple,  less  one  or  more  molecules  of  water. 
The  disaccharides  yield  two  molecules  of  simple  sugars  on  hydrolysis. 
The  two  most  common  disaccharides  are  sucrose  (cane  sugar)  which 
yields  one  molecule  of  glucose  and  one  of  fructose  when  hydrolyzed  by 
dilute  acids  or  inverted  by  an  enzyme  and  maltose  (malt  sugar)  which 
yields  two  molecules  of  glucose. 

In  addition  to  the  sugars  there  are  complex  carbohydrates,  called 
polysaccharides;  these  yield  an  indefinite  number  of  molecules  of  simple 
sugars  on  hydrolysis.  They  are  for  the  most  part  less  soluble  in  water 
than  the  sugars.  One  kind  of  sugar  or  a  mixture  of  different  kinds  may 
be  formed  on  hydrolysis.  If  the  predominant  sugar  produced  is  a  hexose, 
they  are  called  hexosans;  if  a  pentose,  pentosans. 

Hexosans  are  classified  according  to  the  nature  of  the  predominating 
sugar  produced  on  hydrolysis.  Thus  there  are  glucosans  which  include 
starch,  soluble  starch,  dextrin  and  cellulose;  fructosans  such  as  inulin; 
mannans,  a  constituent  found  in  the  wood  and  leaves  of  the  hme,  apple 
and  chestnut,  and  galactans  such  as  agar-agar.  Pentosans  include  gums, 
mucilages  and  pectins,  on  which  the  jelling  properties  of  fruit  depend. 
The  relationships  of  the  carbohydrates  are  shown  diagrammatically  in 
Fig.  17. 

Daihj  and  Seasonal  Fluctuation  in  Leaves. — Though  no  reliable  data 
are  available  on  which  to  base  a  detailed  picture  of  the  carbohydrate 
changes  in  the  leaf,  the  following  statements  may  be  made.^"^  Hexose 
sugars  and  sucrose  increase  during  the  day,  reach  a  maximum  about  mid- 
day, after  which  the  quantity  present  decreases;  these  changes  closely 
parallel  the  temperature  variations  and  probably  the  variations  in  light 
intensity.  There  is  no  diurnal  fluctuation  in  the  amount  of  pentoses  or 
of  pentosans.  As  a  result  of  the  accumulation  of  sugars,  starch  is  formed; 
the  process  occurs  only  in  cell  plastids,  either  in  chloroplasts  which  are 
green  or  in  leucoplasts  which  are  colorless.  Species  vary  greatly  in  their 
capacity  to  form  starch.  Many  plants — the  onion,  for  instance — form 
none  at  all.  Starch  and  sucrose  formation  in  the  leaf  are  only  temporary. 
The  carbohydrates  are  continuously  conducted  from  the  leaf  as  hexoses, 
which  occur  in  greater  amounts  than  other  sugars  in  the  conducting 


168 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


>  O- 


Ml 


rt  o  c 

-^Bi 

^.^ 

C    03 

flfS 

O    o 

SM 


// 


-^2 


03     fl 

II 

1 


Sj        rt        S 


MANUFACTURE  AND  UTILIZATION  OF  CARBOHYDRATES      169 

tissues.  The  starch  present  in  the  leaf  accumulates  there  only  because 
the  manufacture  of  sugars  is  proceeding  more  rapidly  than  their  removal. 
During  the  night  the  starch  is  digested  by  enzymes  to  maltose  and  the 
maltose  to  glucose,  which  then  passes  out  of  the  leaf. 

The  seasonal  variation  in  the  carbohydrate  supply  of  leaves  has  been 
studied  by  Michel  Durant.^^''  He  distinguishes  two  stages  in  the  life 
of  a  leaf:  (1)  a  period  of  carbohydrate  synthesis  and  polymerization, 
extending  from  the  time  the  leaves  begin  to  function  until  the  end  of 
summer  or  in  annual  plants  until  the  seeds  begin  to  develop,  during 
which  period  carbohydrate  assimilation  is  active  and  carbohydrates  of  all 
types  increase  in  amount;  (2)  a  period  of  hydrolysis  and  simplification 
beginning  about  the  time  when  the  leaves  turn  yellow.  This  is  marked 
by  a  decrease  in  the  amount  of  compound  carbohydrates  and  a  further 
accumulation  of  simple  sugars.  The  development  of  the  abscission  layer 
at  the  base  of  the  leaves  of  deciduous  plants  is  correlated  with  this 
accumulation  of  simple  sugars  in  the  leaf  blade,  so  that  their  removal 
to  the  branch  is  soon  stopped.  The  sugars  increase  until  they  are  re- 
spired, fermented  or  washed  out  by  rain.  In  leaves  of  annual  plants,  a 
larger  proportion  of  these  sugars  is  removed  to  the  developing  seeds  and 
fruits;  consequently,  accumulation  of  simple  sugars  is  less  pronounced 
than  in  tree  leaves.  Nevertheless,  at  the  end  of  this  second  period 
there  are  always  appreciable  amounts  of  carbohydrates  left  in  the  leaf. 

In  evergreen  leaves,  the  accumulation  of  simple  sugars  in  the  fall 
and  winter  is  accentuated  by  photosynthesis  which  continues  and  pro- 
duces appreciable  effects  because  cold  weather  retards  respiration  more 
than  photosynthesis.  Starch  disappears  or  persists  in  small  amounts 
and  disaccharides  containing  fructose,  such  as  sucrose,  are  prevalent. 
In  the  spring,  starch  is  resynthesized  at  the  expense  of  soluble  sugars.  In 
June,  the  polysaccharides  of  the  leaves  decrease,  being  added  to  stores 
in  the  branches  or  used  in  the  development  of  the  fruit.  The  carbohy- 
drate content  remains  low  until  the  end  of  autumn.  In  general,  the  older 
the  leaf,  the  greater  its  carbohydrate  content  and  a  maximum  in  poly- 
saccharides corresponds  to  a  minimum  in  simple  sugars. 

It  has  been  found  that  the  pentosans  form  a  larger  and  larger  propor- 
tion of  the  matter  insoluble  in  alcohol  and  that  the  pentoses  increase  as 
the  season  advances,  the  latter  probably  representing  hydrolytic  products 
of  pentosans.^- 

The  entire  plant  depends  on  the  assimilating  function  of  its  leaves 
for  its  supply  of  carbohydrates  and  of  those  compounds  manufactured 
from  them.  The  carbohydrates  synthesized  in  the  leaves  are  trans- 
located as  hexoses  through  the  phloem  to  all  parts  of  the  plant  where  they 
are  either  stored  or  utilized  in  ways  specified  later. 

Forms  of  Storage. — Since  starch  is  the  most  common  form  in  which 
carbohydrates  are  stored,  it  is  important  to  consider  the  structure  of  the 


170  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

starch  molecule  in  order  to  gain  some  idea  of  the  factors  involved  in  its 
formation.  When  starch  is  hydrolyzed  slowly,  it  yields  maltose  and 
dextrin.  Both  of  these  yield  glucose  on  further  hydrolysis.  Corn 
starch  contains  palmitic  acid,  a  fatty  acid  and  a  related  unsaturated 
compound.  These  fatty  substances  are  liberated  only  after  hydrolysis 
and  are  probably  attached  to  the  carbohydrate  of  the  starch  molecule.  ^^^ 
There  is  enough  fatty  acid  in  the  corn  starch  molecule  to  make  com- 
mercially profitable,  in  the  manufacture  of  glucose  from  corn  starch, 
the  use  of  this  residue  as  soap  stock.  Moreover,  starch  probably  is  not 
chemically  homogeneous.  At  least  two  substances  with  distinct  prop- 
erties have  been  separated  and  called  amylose  and  amylopectin. 

When  the  concentration  of  hexoses  is  sufficiently  great,  starch  is 
usually  formed  in  the  plastids.  In  fact,  leaves  of  plants  such  as  the 
onion  which  do  not  ordinarily  form  starch,  will  do  so  when  floated  on  a 
10  per  cent,  solution  of  fructose. 

Starch  will  be  formed,  therefore,  whenever  the  concentration  of 
sugars  reaches  a  certain  point  and  other  conditions  such  as  temperature 
permit.  In  the  summer  and  early  autumn,  starch  is  stored  in  the 
branches.  In  the  peach,  great  amounts  are  found  in  the  leaf  gaps.  In  the 
younger  apple  shoots,  it  accumulates  predominantly  in  the  pith,  being 
especially  abundant  at  the  nodes. 

The  association  of  fat  with  the  starch  molecule  indicates  that  the 
latter  is  the  starting  point  for  fat  formation  in  plants.  Fatty  oils  there- 
fore may  be  considered  as  a  reserve  food  derived  from  carbohydrates 
especially  in  fruits  like  the  avocado,  in  the  seed  of  fruits  like  the  apple 
and  cocoanut  and  also  over  the  winter  in  the  younger  roots  and  branches. 
Fats  are  esters  which  yield  on  hydrolysis  one  molecule  of  glycerine  and 
three  molecules  of  fatty  acids.  The  commonest  fatty  acids  found  in 
plant  fats  and  oils  are:  (1)  oleic  acid,  in  olive  oil,  almond  oil,  quince  oil, 
cherry-,  plum-,  peach-  and  apricot-kernel  oil;  (2)  linolic  acid,  in  the  oils 
from  pumpkin,  watermelon,  melon,  apple,  pear  and  orange  seeds;  (3) 
palmitic  acid,  in  cocoanut  oil  and  cocoa  butter  and  (4)  dihydroxystearic 
acid,  in  grape-seed  oil.  Fats  contain  less  oxygen  in  proportion  to  the 
carbon  present  in  the  molecule  than  carbohydrates.  They,  therefore, 
yield  more  energy  when  oxidized  and  may  be  regarded  as  concentrated 
energy  in  chemical  combination. 

Sucrose  and  even  glucose  must  at  times  be  considered  forms  of  carbo- 
hydrate storage. 

Seasonal  Fluctuations  of  Stored  Carbohydrates. — The  seasonal  varia- 
tion in  the  carbohydrate  content  of  plants  gives  evidence  of  storage. 

Easily  Hydrolyzable  Carbohydrates. — ^Leclerc  du  Sablon's^'^  deter- 
minations of  the  easily  hydrolyzable  carbohydrate  in  the  roots  and 
branches  of  the  pear  and  chestnut  are  given  in  Table  59.  This  type  of 
carbohydrate  which  includes  sugars,  starch  and  other  easily  hydrolyzed 


MANUFACTURE  AND  UTILIZATION  OF  CARBOHYDRATES      171 


Table  59. — Easily  Hyduolyzed  Carbohydrate  in  Percentages  of  Dry  Weight 

IN  Pear  and  Chestnut  Trees'" 

Pear 


Date 

Branches 

Roots 

Feb.  18 

23.0 
21.3 
23.7 

24.7 
25.7 
25.4 

39  3 

Apr.  13 

22  4 

June  16 

27  9 

Aug.  4 

29  2 

Sept.  24 

33  8 

Dec.  1 

29  3 

Chestnut 

Jan.  11 

24.7 
24.7 
21.5 
19.9 
20.4 
21.1 
25.9 
26.4 
24.7 
23.0 

27  2 

Feb.  26 

25  7 

Mar.  28 

24  7 

May  20 

19  8 

June  22 

21  8 

July  27 

24  3 

Sept.  12 

30  3 

Oct.  19 

29  1 

Nov.  22 

28  9 

Dec.  12 

27  3 

polysaccharides,  but  not  crude  fiber,  is  at  a  maximun  in  September 
and  at  a  minimum  in  May.  Moreover  there  is  a  steady  increase  from 
May  to  September  and  a  fairly  steady  decrease  from  September  to  May. 
Similar  data  showing  the  variations  in  the  easily  hydrolyzed  polysac- 
charide of  7-year  old  apple  trees  are  given  in  Table  60.     Here  also  much 


Table  60. 


-Easily  Hydrolyzed  Carbohydrate  in  Percentages  of  Dry  Weight 
IN  7-YEAR  Old  Apple  Trees^^ 
(Each  figure  is  the  average  of  analyses  from  two  trees) 


Dormant, 
Dec.  3 


Buds 

In 

Growth 

swelHng, 

bloom, 

over. 

Apr.  20 

May  18 

July  12 

30.54 

30.31 

19.21 

25.22 

29.38 

13.24 

26.59 

35.75 

11.68 

32.26 

31.58 

18.48 

30.03 

31.29 

16.08 

25,07 

34.08 

17.80 

32.23 

38.38 

21.77 

28.90 

36.47 

36.47 

31.87 

Leaves 
falling, 
Oct.  12 


New  growth 

1-year  old  branches . 
2-year  old  branches 
3-year  old  branches . 
4-year  old  branches . 
5-year  old  branches . 

Trunk 

Large  roots 

Small  roots 


21.36 
22.13 
22.41 
20.44 
20.43 
25 .  83 
29.90 
29.36 


27.34 
26.50 
26.72 
26.10 

27.88 
27.28 
27.96 
32.02 
33.88 


172 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


the  same  picture  is  presented  except  an  increase  from  December  to  April, 
accounting  for  which  is  difficult.  The  minimum  in  May  is  apparent,  but 
the  maximum  in  September  does  not  appear,  as  samples  were  not  collected 
at  that  time. 

In  all  the  data  presented,  the  roots  have  shown  a  higher  percentage 
and  a  greater  fluctuation  in  carbohydrate  than  the  shoots.  However, 
this  does  not  indicate  a  greater  absolute  carbohydrate  content.  Esti- 
mates by  Curtis^^  indicating  the  probable  relationships  at  the  time  of  bud 
swelling  (April)  are  shown  in  Table  61.     According  to  these  figures  the 


Table  61.- 


-EsTiMATED  Number  of  Pounds  of  Carbohydrate  in  Tops  and  Roots 
OF  A  7-year  Old  Apple  Tree^'' 


1  year  twigs 1 

Older  branches 5 

Trunk 5 


10 


25 


Large  roots 5.71 

Small  roots 2 .  43 


Total 13.24 


Total . 


14 


portions  of  a  tree  above  ground  contain  half  again  as  much  as  the  roots. 
The  conditions  found  in  apple  spurs  are  shown  in  Table  62.  These 
figures  evidently  are  comparable  to  the  data  of  I^e  Clerc  du  Sablon  on  the 
pear  and  chestnut. 


Table  62. 


-Total  Carbohydrate  (not  Including  Crude  Fiber)  of  Apple  Spurs' 
(In  percentages  of  dry  weight) 


Bearing  (average 
of  three  trees) 


Non-bearing 

(average  of  two 

trees) 


March . . 
May  13. 
June  25. 
Sept.  2. 
Nov.  19 
Jan.  24. 


25.1 
24.0 
25.2 
30.1 

24.5 
23.9 


The  increase  in  carbohydrate  from  May  to  September  is  explained  by 
the  assimilatory  activity  of  the  leaves.  The  decrease  from  September 
to  May  must  be  attributed  to  several  factors.  The  major  part  is  due  to 
the  use  of  carbohydrates  for  the  formation  of  other  substances — probably 
of  nitrogenous  compounds  which  increase  in  September  and  of  fatty 
substances,  which  are  discussed  presently.  The  decrease  in  carbo- 
hydrate is  also  in  part  the  result  of  consumption  in  respiration,  which 
proceeds  from  September  to  May,  but  most  actively  after  growth  has 
begun  and  in  part  the  result  of  translocation  into  the  newly  developing 
leaves,  flowers  and  eventually  fruits.     Hence  the  lower  minimum  in  the 


MANUFACTURE  AND  UTILIZATION  OF  CARBOHYDRATES      173 

carbohydrate  content  of  bearing  spurs  in  May  may  be  associated  with 
flowering.  The  higher  maximum  in  these  same  spurs  in  September  is 
probably  connected  with  the  development  of  specialized  tissues  in  the 
purse  during  fruit  development. 

The  study  of  the  various  types  of  carbohydrate,  particularly  starch 
and  sugars,  shows  similar  seasonal  fluctuations  despite  some  variation. 

Starch. — The  only  analytical  data  on  the  seasonal  variation  in  starch 
content  are  on  spurs.  In  woody  tissues,  starch  is  a  relatively  small 
fraction  of  the  total  polysaccharides,  but  probably  a  significant  fraction 
of  the  available  carbohydrates.  Figure  18  shows  the  starch  variations 
in  bearing,  non-bearing  and  barren  spurs  of  the  apple.  ^°° 


5 

\h 

\ 

^ 

J 

A 

u 

\ 

\ 

y 

ft 

.4 

A 

\ 
\ 

\^ 

\ 

\ 

\ 

/ 

/ 

/ 

//e 

s 

\ 

\ 

\ 

\ 

y 

, 

/ 

J 

^^^ 

•v^ 

\ 

V 

1 

'l 

^ 

' 

^^ 

\ 

2 

J 

\ 

\\ 

\ 

/ 

/ 

V 

1 

/ 

/ 

N 

\ 

^v 

^^ 

-vL. 

:r-B 

\ 

A' 

\i 

// 

/; 

/ 

B 

— 

s 

^ 

S 

^ 

W 

B 

\ 

^ 

/ 

/ 
/ 

1/ 

/ 

^ 

\ 

^ 

r  ^ 

\^ 

s^ 

// 

^/ 

8 

"■'^ 

/ 

0 

, 

z:  s: 


c^ 


Fig.  18. — Starch  content  of  apple  spurs  in  percentages  of  dry  weight;  bearing  spurs 
represented  by  continuous  lines,  non-bearing  spurs  by  broken  lines  and  barren  spurs  by 
dot-dash  lines.      {After  Hooker. ^^'') 


There  are  two  maxima  for  starch  and  two  minima.  This  was  shown 
microchemically  by  Mer  and  d'Arbaumont.'^^  The  maximum  in  Septem- 
ber and  the  minimum  in  May  correspond  to  the  maximum  and  minimum 
for  total  carbohydrates.  The  second  minimum  in  January  and  the 
second  maximum  in  March  are  due  to  conversion  of  starch  to  sugars  and 
a  resynthesis  of  starch  in  spring  just  before  vegetation  commences.  The 
second  maximum  is  not,  however,  so  high  as  the  first — except  in  bearing 
spurs — which  indicates  that  a  certain  amount  of  carbohydrate  has  been 
consumed  in  respiration  or  used  for  the  formation  of  other  substances. 
Determinations  of  the  ether  extract  permit  an  estimate  of  the  fat  and  oil 
content  and  show  that  fats  increase  during  the  winter.  The  previous 
discussion  of  the  structure  of  starch  indicates  that  this  is  the  point 


174 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


of  departure  for  fat  formation.  Table  63  shows  the  seasonal  variation 
in  ether  extract  in  7-year  old  apple  trees.  It  is  evident  that  the  younger 
the  tissue,  the  more  fat  it  contains  and  that  the  fat  content  is  at  a  maxi- 
mmn  just  before  active  growth  begins  and  at  a  minimum  after  active 
growth  is  over. 

Table  63. — Ether  Extract  in  Percentages  of  Dry  Weight  in  7-year  Old  Apple 

Trees23 
(Each  figure  is  the  average  of  analyses  from  two  trees) 


Dormant, 
Dec.  3 

Buds 
swelling, 
Apr.  20 

3.26 

5.18 

2.77 

3.58 

2.49 

2.92 

1.75 

1.50 

1.28 

1.07 

0.85 

0.96 

2.25 

1.86 

6.79 

5.03 

In 
bloom, 
May  18 


Growth 

over, 
July  12 


Leaves 
falling, 
Oct.  12 


New  growth 

1-year  branches 
2-year  branches 
3-year  branches 
4-year  branches 
5-year  branches 

Trunk 

Large  roots 

Small  roots 


5.00 
3.03 
2.39 
1.57 
1.14 
0.79 
2.02 
4.06 


3.15 
2.68 
2.31 
1.99 
1.31 
1.18 
0.72 
2.38 
5.85 


4.11 
3.01 
2.92 
2.71 
1.07 
0.91 
0.70 
1.31 
6.55 


Characteristic  differences  between  the  starch  content  of  bearing 
and  non-bearing  spurs  appear  in  Fig.  18.  In  winter  the  spurs  with 
fruit  buds  have  more  starch.     Moreover  starch  accumulation  commences 


/J 

/ 
/ 

B 

^, 

V. 

} 

'A 

^ 

N 

\ 

\ 

^ 

cs 

^ 

>' 

1^ 

J 

: — ~. 

N 

B 

7^ 

^ 

^ 

^ 

^ 

^ 

^ 

^ 

S 

^ 

^ 

r' 

2:    s: 


Fig.  19. — Total  sugar  content  of  apple  spurs  in  percentages  of  dry  weight;  bearing 
spurs  represented  by  continuous  lines,  non-bearing  spurs  by  broken  lines  and  barren  spurs 
by  dot-dash  lines.      {After  Hooker. ''■°'>) 

in  non-bearing  spurs  in  May  and  in  bearing  spurs  in  June.  This  differ- 
ence is  connected  with  carbohydrate  utilization  by  the  fruit.  The 
relation  of  this  to  fruit  bud  differentiation  is  discussed  later. 

Sugars. — The  seasonal  variation  in  the  sugar  content  of  spurs  is 
shown  in  Fig.  19.     The  rapid  drop  in  sugar  during  the  spring  is  explained 


MANUFACTURE  AND  UTILIZATION  OF  CARBOHYDRATES     175 

by  respiration,  translocation  to  the  leaves  and  fruit,  and  utilization  in  the 
formation  of  complex  carbohydrates.  The  assimilatory  activity  of  the 
leaves  soon  restores  the  sugar  content  of  the  spurs,  but  a  marked  increase 
does  not  commence  until  September,  This  is  due  to  continued  demands 
for  sugar  by  the  developing  fruit  on  bearing  spurs  and  to  starch  accimiula- 
tion  in  non-bearing  spurs.  The  increase  in  sugars  after  September  is 
associated  with  the  decrease  in  starch  during  this  period  and  represents  a 
partial  conversion  of  starch  to  sugars.  Some  of  this  sugar  is  sucrose, 
a  form  in  which  carbohydrate  is  stored  during  the  winter,  as  the  figures 
in  Table  6-4  show. 


Table  04.- 

-AvER.\GE  Non-reducing  Sugar  Content 
OF  Dry  Weight'ou 

OF  Spurs  in 

Percentages 

Bearing 
spurs 

Non-bearing 
spurs 

Barren 
spurs 

March 

0.59 
0.44 
0.00 
0.09 
1.27 
0  56 

0.47 
0.27 
0.05 
0.45 
0.77 
2  40 

0  97 

May  13 

June  26 

0.45 
0  19 

Sept.  2 

Nov.  14 

Jan.  24. 

0.35 
0.91 
1  66 

The  sugar  used  in  the  development  of  fruit  is  considerable,  as  Table 
65  indicates.  In  the  apple,  the  percentage  and  absolute  amounts  in 
the  fruit  increase  steadily,  the  rate  of  increase  becoming  greater  as 
maturity  approaches.  This  holds  for  prunes  also.^^^  In  pears  the 
percentage  decreases  at  first  and  then  increases,  while  the  absolute 
amounts  increase  steadily.  In  either  case  the  increase  in  absolute 
amount   extends   to   the  end  of  August  or  the  middle  of  September. 

Michel  Durant^^''  points  out  that  a  period  of  carbohydrate  synthesis  followed 
by  one  of  hydrolysis  and  simplification  is  found  in  fruits  as  well  as  in  leaves. 
Ripe  fruit  therefore  contains  more  sugar  than  unripe  fruit.  The  increase  in  the 
sugar  content  may  continue  even  after  the  fruit  is  picked.  This  occurs  in  drying 
prunes  when  sugar  is  formed  by  the  hydrolysis  of  starch.  If  prunes  after 
removal  from  the  tree  are  exposed  to  the  sunlight  for  2  or  3  days,  their  sugar 
content  increases,  but  after  5  days'  exposure  their  sugar  is  rapidly  consumed  in 
respiration  and  fermentation.'*^ 

In  recapitulation,  it  is  emphasized  that  the  carbohydrate  supply 
of  the  plant  is  manufactured  in  the  leaves  and  that  the  leaves  supply  the 
entire  plant.  In  consequence,  movement  of  carbohydrate  is  usually 
away  from  the  leaves  to  the  growing  points,  cambium  and  storage  organs. 
Carbohydrate  is  stored  mostly  in  the  immediate  vicinity  of  places  where 
it  may  later  be  used.     Thus  the  work  of  Magness'^s  andof  Curtis"  indi- 


176  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Table  65. — Reducing  Sugar  Content  of  Devei.oping  Apples  and  Pears"' 


Apples 

Date 

Pears 

Pleissner 
Rambour 

Red  Easter 
Caville 

Date 

Salzburg 

Liegel's  Honey 

Per- 
centage 
of  dry 
weight 

Grams 

in  1,000 

fruits 

Per- 
centage 
of  dry 
weight 

Per- 
centage 
of  dry 
weight 

Grams 

in  1,000 

fruits 

Per- 
centage 
of  dry 
weight 

Grams 

in  1,000 

fruits 

Grams 
in  1,000 

fruits 

June  2 

June  12 

June  22 

July  2 

July  12 

July  22 

Aug.  1 

Aug.  11 

Aug.  21 

Aug.  31 

Sept.  10 

Sept.  20 

Sept.  30 

Dec.  12 

3.05 
10.70 
14.91 
22.90 
24.19 
17.11 
39.45 
34.65 
39.69 
43.07 
51.28 
60.04 
52.99 

0.9 

22.0 

97.0 

368.0 

870,0 

1,150.0 

2,540.0 

4,260.0 

4,250.0 

6,600.0 

7,530.0 

10,850.0 

9,630.0 

3.28 
6.75 
12.70 
16.51 
19.78 
20.29 
23.19 
26.42 
30.17 
31.47 
35.41 
36.28 
33.73 
48.14 

0.7 

8.8 

43.0 

150.0 

370.0 

670.0 

950.  0 

1,400.0 

1,740.0 

2,400.0 

3,040.0 

3,. 550.0 

3,200.0 

4,730.0 

May  26 

June  5 

June  15 

June  25 

July  5 

July  15 

July  25 

Aug.  4 

Aug.  14 

Aug.  24 

Sept.  3 

Sept.  8 

4.98 

2.17 

1.66 

1.92 

2.78 

4.56 

7.16 

16.43 

30.03 

35.02 

51 .  35 

1.0 

2.7 

7.7 

18.0 

36.0 

95.0 

218.0 

637.0 

1,660.0 

2,230.0 

3,590.0 

4,180.0 

5.03 
3.26 
2.50 
4.56 
6.74 
12.01 
23.60 
36.49 
43.68 
50.61 

0.8 

3.6 

10.2 

32.0 

68.0 

175.0 

536.0 

770.0 

1,520.0 

1,800.0 

cate  that  the  carbohydrate  stores  in  the  roots  do  not  return  to  the  tops. 
They  are  used  by  the  roots.  Cambial  activity  depends  on  the  carbo- 
hydrate stored  in  the  medullary  rays  and  the  starch  sheath.  Bud 
development  in  the  spring  depends  largely  on  the  carbohydrate  stored 
in  the  pith  or  leaf  gap  near  the  bud. 

CARBOHYDRATE  UTILIZATION 

Carbohydrates  are  used  in  any  one  of  the  following  ways: 

1.  For  tissue  building,  that  is  for  the  construction  of  other  carbo- 
hydrates, or  of  different  substances  manufactured  from  carbohydrates, 
which  enter  into  the  composition  of  plant  cells. 

2.  For  the  retention  of  moisture. 

3.  To  increase  osmotic  concentration. 

4.  As  a  source  of  energy. 

In  Tissue  Building. — According  to  Czapek,  glucose  is  a  constituent 
of  every  living  cell  and  therefore  may  be  considered  a  necessary  part 
of  the  chemical  equipment  of  living  matter.  The  great  value  of  glucose 
in  metabolism  is  probably  associated  with  the  ease  with  which  it  is  altered 
to  a  number  of  different  but  related  compounds.  Through  its  enolitic 
form  it  may  be  changed  to  fructose  and  mannose.  Glucose,  fructose 
and  mannose  exist  in  at  least  five  forms  each.  Wherever  glucose  is 
present  in  solution,  as  in  protoplasm,  certain  of  these  forms — depending 


MANUFACTURE  AND  UTILIZATION  OF  CARBOHYDRATES      177 

on  the  prevailing  conditions — tend  to  develop  until  a  complex  equilib- 
rium is  established.  Since  each  form  has  different  physical  and  chemical 
properties  the  multiplicity  of  ways  in  which  glucose  may  become  the 
basic  material  for  a  great  diversity  of  physiological  processes  is  evident. 
Besides  the  forms  in  which  glucose  may  be  stored  temporarily,  it  is  utihzed 
for  the  construction  of  the  permanent  framework  of  the  plant,  being 
the  substance  from  which  many  forms  of  carbohydrate  as  well  as  of 
other  groups  of  organic  compounds  are  made.  The  cellulose  wall  is 
secreted  by  each  cell  from  its  supply  of  hexose  sugars.  So  also  is  the 
middle  lamella,  which  is  a  pentosan,  a  salt  of  pectic  acid.  It  has  been 
suggested  that  fats  probably  are  derived  from  carbohydrates  and  that 
starch  is  presumably  an  intermediate  stage  in  fat  formation.  Glucosides 
give  rise  to  one  or  more  molecules  of  sugar  on  hydrolysis  and  it  is  shown 
presently  that  organic  acids  arise  from  the  respiration  of  carbohydrates. 
Little  is  known  concerning  the  seasonal  quantitative  variation  in 
many  of  these  contituents.  It  may  be  said,  however,  that  crude  fiber, 
which  is  composed  chiefly  of  cellulose  and  lignin  increases  steadily  with 
age  in  roots  and  branches  and  that  seasonal  variations  are  insignificant 
in  comparison  to  this  regular  trend. 

Complete  vegetative  development  depends  on  an  adequate  carbohydrate 
supply  and  a  plant  is  unable  to  attain  its  full  size  and  ordinary  shape  in  dark- 
ness or  particularly  in  the  absence  of  red  light.  This  is  true  especially  of  leaves. 
If  they  are  supplied  with  carbohydrates  in  a  form  in  which  they  can  be  absorbed, 
the  effect  of  the  absence  of  light  on  the  size  of  the  leaf  can  largely  be  eliminated. 
However,  different  plants  show  more  or  less  characteristic  responses  to  an  ab- 
sence of  light  in  this  respect,  which  seems  to  be  associated  with  the  amount  of 
carbohydrate  that  tends  to  accumulate  when  the  leaves  are  kept  in  darkness. 
Bean  leaves,  for  example,  contain  small  amounts  of  carbohydrates  when  kept 
in  the  dark;  consequently  the  leaves  do  not  grow.  This  is  the  case  with  most  of 
the  fruit  plants.  In  a  certain  number  of  plants  such  as  wheat,  starch  is  always 
present  in  the  leaves  and  considerable  amounts  of  carbohydrate  accumulate 
even  when  the  leaves  are  kept  in  darkness;  these  attain  their  usual  size  under 
such  conditions,  though  they  may  be  narrower  than  the  leaves  of  illuminated 
plants.'''^  There  are,  however,  other  peculiarities  in  the  form  and  structure  of 
plants  grown  in  darkness  which  cannot  be  attributed  in  any  way  to  the  carbo- 
hydrate supply. 

In  Retaining  Moisture. — Pentosans  have,  according  to  Spoehr,i" 
the  property  of  holding  moisture.  Certain  pentosans  develop  under 
conditions  where  the  moisture  supply  is  limited  and  furnish  the  plant 
with  a  water-retaining  mechanism  which  minimizes  the  effect  of  the  water 
deficiency.  The  moisture  held  by  pentosans  seems  to  be  in  a  colloidal 
mbcture,  where  it  is  retained  tenaciously  and  offers  resistance  to  desic- 
cating agencies.  This  colloidally  held  water  should  be  differentiated 
from  free  water  since  it  is  characterized  by  distinct  physical  properties. 


178  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Increasing  Osmotic  Concentration. — Sugars  are  important  to  the 
plant  because  they  are  osmotically  active.  Since  the  osmotic  concen- 
tration depends  on  the  number  of  molecules  and  not  on  their  size,  it  is 
evident  that  the  formation  of  disaccharides  from  simple  sugars  reduces 
the  osmotic  concentration.  Conversely,  the  hydrolysis  of  compound 
sugars  or  polysaccharides  to  simple  sugars  increases  the  osmotic  concen- 
tration. Thus  the  building  up  and  splitting  down  of  carbohydrates 
regulates  the  osmotic  concentration.  On  the  other  hand,  it  unques- 
tionabl}^  plays  an  important  part  in  controlling  synthetic  and  hydrolytic 
processes.  Thus  compound  sugars  and  especially  starch  are  usually 
produced  wherever  the  concentration  of  sugars  is  high,  though  other 
factors  are  involved,  particularly  enzymes.  The  hydrolysis  of  compound 
carbohydrates  proceeds  most  rapidly  when  the  concentration  of  sugars 
is  low;  therefore  their  consumption  in  respiration,  their  removal  to  other 
organs  and  their  use  in  the  formation  of  other  compounds,  particularly 
of  substances  like  cellulose  that  are  insoluble  and  consequently  not 
involved  in  the  osmotic  system,  accelerate  the  processes  of  hydrolysis. 

As  a  Source  of  Energy. — One  of  the  most  important  properties  of 
carbohydrates  is  that  of  yielding  energy  in  the  process  of  respiration.  In 
fact  most  of  the  energy  used  by  plants  and  animals  is  the  stored  potential 
energy  of  fats  and  carbohydrates.  By  means  of  carbohydrates  the  roots 
are  able  to  utilize  the  energy  of  sunlight. 

Respiration  involves  several  processes.  There  are  many  theories,  but 
according  to  the  most  suggestive,  respiration  consists  of  two  main  reac- 
tions; one  is  a  process  of  cleavage,  in  which  the  simple  carbohydrate 
molecule  is  split  into  carbon  dioxide  and  certain  intermediate  substances, 
probably  alcohols  or  acids;  the  other  is  a  process  of  oxidation,  in  which 
these  intermediate  substances  are  oxidized  to  carbon  dioxide  and  water. 
The  first  process  is  essentially  a  fermentation  for  which  the  enzyme, 
zymase,  is  essential.  The  second  process — of  oxidation — depends  on 
enzymes  called  peroxidases  which  act  only  in  the  presence  of  peroxides. 
Peroxidases  supposedly  transfer  oxygen  from  organic  peroxides  to  the 
products  of  cleavage  formed  during  the  first  process  in  respiration, 
oxidizing  them  to  carbon  dioxide  and  water.  According  to  some  investi- 
gators there  are  other  enzymes  involved  but  if  this  be  true,  they  play 
subsidiary  parts  and  need  not  be  considered  here. 

In  general  the  amount  of  carbon  dioxide  given  off  is  approximately 
equal  to  the  amount  of  oxygen  used  in  respiration  so  that  the  respiration 
of  a  hexose  may  be  represented  by  the  formula  C6H12O6  +  6O2  =  6H2O 
+  6CO2  +  energy.  The  two  processes  of  respiration,  cleavage  and 
oxidation,  are  more  or  less  independent  of  each  other,  so  that  an  accumu- 
lation of  acid  may  occur  in  plant  tissues  during  periods  of  active  respira- 
tion, through  the  incomplete  oxidation  of  carbohydrates  and  other  sub- 
stances.   The  inverse  correlation  existing  between  starch   content  and 


MANUFACTURE  AND   UTILIZATION  OF  CARBOHYDRATES      179 

acidity  in  apple  spurs  is  shown  in  Figs.  20  and  21,  In  the  spring,  starch 
and  sugar  decreased  rapidly  in  these  spurs  and  acidity  rose.  This  may  be 
interpreted  as  indicating  the  hydrolysis  of  starch  to  sugar  and  the  incom- 


\ 

\h 

/ 

\ 

^ 

\ 

/ 

\ 

,-^ 

^^ 

-N 

1 

\l 

A 

\, 

\ 

^ 

^ 

\ 

J 

\ 

/ 

\ 

^ 

X 

/ 

'\ 

s. 

se 

^ 

\ 

^ 

'^ 

\ 

N 

/ 

\ 

\ 

,r 

V 

-I 



r< 

-^ 

■~~» 

\ 

/ 

\ 

A 

w 

1 

\ 

f 

y 

/ 

/ 

/ 

Fig.  20.- — Starch,  reducing  sugar  content  and   titratable  acidity  of  bearing  apple  spurs 
compared.      (After  Hooker .''^'>°) 

plete  oxidation  of  the  sugar  to  acid.  Some  of  the  decrease  in  sugar  is 
explained  by  removal  to  the  developing  leaves  and  flowers.  The  increase 
in  acidity  in  the  spring  lasted  longer  and  reached  a  higher  maximum  in 


/ 

/^ 

\ 

/^ 

{ 

\ 

\ 

\ 

'b 

y 

\ 

s 

/ 

/ 

\ 

\ 

/ 

\ 

/ 

/ 

\ 

/ 

"^ 

7 

.^C/ 

D/r 

^ 

\ 

^ 

^ 

^ 

A 

^ 

/ 

,-^P 

b^- 

■^ 

^ 

^ 

\> 

^ 

nuc 

ING 

^ 

i^ 

\ 

y 

J 

Fig.  21.— Starch,  reducing  sugar  content  and  titratable  acidity  of  non-bearing  apple  spurs 
compared.      (After  Hooker. '^'^°) 

bearing  spurs.  At  the  same  time  the  consumption  of  reducing  sugars 
was  more  complete.  This  may  be  associated  with  greater  respiratory 
activity  in  flowers.  Respiratory  activity  is  particularly  pronounced 
in  floral  parts,  germinating  seeds  and  growing  parts  in  general. 


180  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Relation  to  Pigment  Formation, — A  supply  of  carbohydrates  is  necessary  for 
the  development  of  certain  pigments  in  leaves,  flowers  and  fruits.  Laurent^^*^ 
showed  that  fruit  pigments  are  of  two  types ;  some  develop  only  as  a  result  of 
direct  exposure  to  light;  others  do  not  require  direct  illumination  of  the  fruit 
but  for  their  development  the  leaves  must  be  able  to  manufacture  carbohydrates 
and  the  connection  between  the  leaves  and  the  fruit  must  not  be  interrupted. 
Kraus^^^  suggests  that  pigments  of  both  sorts  occur  in  apples.  The  effect  of 
low  temperature  or  parasitic  attack  in  increasing  the  pigmentation  of  fruit  or 
leaves  is  attributed  to  an  attendant  accumulation  of  sugars,  especially  glucose, 
fructose  and  sucrose. 

Summary. — The  elaborated  plant  foods  used  in  tissue  building  are 
manufactured  from  the  nutrient  materials  obtained  from  the  soil  and  air 
at  a  rate  depending  principally  on  (1)  the  available  supply  of  the  several 
materials  including  water,  (2)  the  intensity,  duration  and  quality  of  the 
light  reaching  the  plant,  (3)  the  amounts  of  the  green  leaf  pigments, 
(4)  temperature  and  (5)  the  presence  of  certain  enzymes.  Any  of  these 
factors  of  the  plant's  environment  or  composition  may  become  limiting 
in  plant  food  synthesis,  their  degree  of  importance  varying  with  condi- 
tions. The  immediate  products  of  photosynthetic  activity  of  the  plant 
are  oxygen  and  carbohydrates.  Oxygen  for  the  most  part  is  set  free 
and  is  in  effect  a  by-product.  Glucose  is  assumed  to  be  the  first  synthetic 
product  of  photosynthesis.  Glucose  may  be  considered  a  starting  point 
for  the  formation  of  more  complex  substances,  such  as  the  other  hexoses, 
disaccharides,  polysaccharides,  pentosans  and  pentoses.  Starch  is  the 
most  common  form  in  which  carbohydrates  are  stored.  They  are  also 
stored  frequently  as  sugars  and  sometimes  they  are  transformed  into 
fats.  The  seasonal  distribution  of  the  more  important  of  these  materials 
is  discussed.  Their  storage  is  more  common  in  or  near  the  prgans  where 
they  are  later  used.  Carbohydrates  are  used  principally  for  new  tissue 
building,  for  the  retention  of  moisture,  for  increasing  osmotic  concentra- 
tion and  as  a  source  of  energy.  Glucose  particularly  is  a  basic  material 
in  the  construction  of  plant  tissues;  for  a  great  diversity  of  physiological 
processes,  pentosans  are  particularly  important  because  of  their  water- 
retaining  capacity.  Sugars  are  important  in  determining  osmotic 
concentration.  Carbohydrates  supply  energy  in  the  process  of  respira- 
tion.    The  formation  of  certain  pigments  also  depends  on  carbohydrates. 


CHAPTER  X 

THE  INITIATION  OF  THE  REPRODUCTIVE  PROCESSES 

The  initiation  of  the  reproductive  processes  of  the  plant  should  be 
considered  in  the  light  of  chemical  conditions  and  the  concurrent  mor- 
phological changes. 

THE  DEVELOPMENT  OF  THE  FRUITFUL  CONDITION 

There  is  much  evidence  that  conditions  associated  with  carbohydrate 
accumulation   have    an   important   relation   to   fruitfulness   in    plants. 

The  Response  of  the  Plant  to  Changes  in  Relative  Amounts  of 
Nitrogen  and  of  Carbohydrates. — Kraus  and  Kraybilli^^,  studying  the 
effects  on  the  tomato  of  various  treatments,  found  that  striking  differences 
in  chemical  composition  and  in  behavior  with  respect  to  fruitfulness  and 
vegetative  growth  could  be  produced  by  controlling  the  environmental 
conditions.     They  summarize  their  work  as  follows: 

"1.  Plants  grown  with  an  abundant  supply  of  available  nitrogen  and  the 
opportunity  for  carbohydrate  synthesis,  are  vigorously  vegetative  and  unfruit- 
ful. Such  plants  are  high  in  moisture,  total  nitrogen,  nitrate  nitrogen  and  low  in 
total  dry  matter,  free  reducing  substances,  sucrose  and  polysaccharides. 

"2.  Plants  grown  with  an  abundant  supply  of  nitrogen  and  then  transferred 
and  grown  with  a  moderate  supply  of  available  nitrogen  are  less  vegetative  but 
fruitful.  As  compared  with  the  vegetative  plants,  they  are  lower  in  moisture, 
total  nitrogen,  and  nitrate  nitrogen,  and  higher  in  total  dry  matter,  free  reducing 
substances,  sucrose  and  polysaccharides. 

'•'3.  Plants  grown  with  an  abundant  supply  of  nitrogen  and  then  transferred 
and  grown  with  a  very  low  supply  of  available  nitrogen  are  very  weakly  vegeta- 
tive and  unfruitful.  As  compared  with  the  vegetative  plants,  they  are  very  much 
lower  in  moisture  and  total  nitrogen  and  are  lacking  in  nitrate  nitrogen;  they 
are  much  higher  in  total  dry  matter,  free  reducing  substances,  sucrose,  and  poly- 
saccharides." 

Three  typical  effects,  measured  principally  in  terms  of  total  nitrogen, 
carbohydrate  and  moisture  have  been  produced  by  these  three  distinct 
environments.  The  first  is  characteristic  of  vigorous  vegetative  growth. 
"An  abundance  of  moisture  and  mineral  nutrients,  including  nitrates, 
coupled  with  an  available  carbohydrate  supply,  makes  for  increased 
vegetation,  barrenness  and  sterility." ^^^  The  second  condition  represents 
a  readjustment  through  which  the  plant  must  pass  before  it  becomes 
fruitful.  "A  relative  decrease  in  nitrates  in  proportion  to  the  carbo- 
hydrates makes  for  an  accumulation  of  the  latter;  and  also  for  fruitful- 

181 


182  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

ness,  fertility,  and  lessened  vegetation.""^  The  third  condition,  in 
which  "a  further  reduction  of  nitrates  without  inhibiting  a  possible 
increase  of  carbohydrates,  makes  for  a  suppression  both  of  vegetation  and 
fruit  fulness,""^  is  evidently  the  manifestation  of  the  effect  of  a  limiting 
factor,  nitrate  supply.  In  addition  to  these  three,  a  fourth  condition 
was  found.  "Though  there  be  an  abundance  of  moisture  and  mineral 
nutrients,  including  nitrates,  yet  without  an  available  carbohydrate 
supply,  vegetation  is  weakened  and  the  plants  are  non-fruitful.  .  .  . 
The  available  carbohydrate  supply  or  the  possibility  for  their  manu- 
facture or  supply,  constitute  as  much  a  limiting  factor  in  growth  as  the 
available  nitrogen  and  moisture  supply.""^ 

Those  instances  (3  and  4),  in  which  nitrogen  or  carbohydrate  supply 
are  limiting  factors  of  growth,  reveal  the  necessity  of  a  proper  balance 
between  carbohydrate  and  nitrate  supply  for  the  best  vegetative 
development. 

"In  other  words,  this  experiment  indicates  first,  that  the  limitation  of  the 
nitrates  resulted  in  the  suppression  of  growth  and  the  accumulation  of  the  more 
complex  carbohydrates;  second,  that  the  limitation  of  the  carbohydrates,  even 
with  large  quantities  of  available  nitrates  in  the  soil,  results  in  a  suppression  of 
growth;  third,  that  a  rapid  vegetative  extension  results  from  an  adjustment  of 
the  carbohydrates  and  nitrates  relative  to  one  another  so  that  both  may  be 
utilized  in  the  formation  and  expansion  of  such  structures;  and  fourth,  that  such 
a  relationship  can  be  secured  either  by  increasing  the  nitrates  without  decreasing 
the  carbohydrates,  or  by  decreasing  the  carbohydrates  without  increasing  the 
nitrates.  While  it  is  apparent  that  the  amounts  of  these  compounds  relative  to 
one  another  would  be  the  same  in  both  the  above  cases,  the  total  amounts  would 
be  greater  in  the  former  and  less  in  the  latter,  a  condition  faithfully  reflected 
in  the  amount  of  growth  produced. "^^* 

In  this  passage  Kraus  and  Kraybill  show  that  there  is  a  distinct 
nutritive  relation  between  the  supply  of  nitrates  and  of  carbohydrates, 
for  vegetative  growth  and  development.  A  carbohydrate  supply 
is  therefore  not  only  just  as  essential  for  the  manufacture  of  protoplasm 
as  are  nitrogen  and  the  essential  mineral  elements,  but  it  combines 
with  them  in  definite  proportion  for  the  building  up  of  the  plant  tissue. 

The  Significance  of  Carbohydrate  Accumulation.  Manufacture  in 
Excess  of  Utilization. — The  differences  between  the  conditions  char- 
acteristic of  vigorous  vegetative  growth  which  is  unfruitful  and  vegeta- 
tion accompanied  by  fruitfulness  are  of  interest.  There  is  no  evidence 
to  show  that  the  utilization  of  nutrient  substances  is  any  different  in  a 
plant  showing  fruit  bud  differentiation  from  that  in  one  which  does  not, 
or  that  the  nutritive  relation  between  carbohydrate  and  nitrate  supply 
in  particular  is  altered.  Kraus  and  Kraybill's  work  shows  that,  in  so 
far  as  the  materials  determined  by  them  are  concerned,  the  chief  differ- 


THE  INITIATION  OF  THE  REPRODUCTIVE  PROCESSES         183 

ence  is  associated  with  circumstances  making  for  carbohydrate  accumula- 
tion in  fruitful  plants  rather  than  a  difference  in  the  method  of  carbo- 
hydrate utilization.  In  other  words,  the  carbohydrate  supplied  must  be 
in  excess  of  the  amount  used. 

Carbohydrate  accumulation  depends  primarily  on  light  conditions.  Under 
experimental  conditions  carbohydrate  assimilation  varies  with  light  intensity, 
in  the  absence  of  other  limiting  factors;  however,  other  factors  become  limiting 
for  plants  grown  in  the  open,  so  that  carbohydrate  assimilation  and  hence  car- 
bohydrate accumulation  depends  on  the  number  of  hours  of  sunlight  rather  than 
on  the  hght  intensity.  ^^'^  Garner  and  Allard^i  have  shown  experimentally  that 
an  increase  in  the  duration  of  light  exposure  determines  f ruitfulness  in  some  plants 
and  they  suggest  that  the  daily  increase  in  duration  of  illumination  which  reaches 
a  maximum  on  June  21,  may  have  an  important  relation  to  the  time  at  which 
these  plants  blossom.  It  is  interesting  to  observe  that  fruit  bud  differentiation 
in  the  apple  usually  occurs  the  latter  part  of  June  or  early  part  of  July,  though 
it  has  been  observed  to  occur  at  almost  every  season.  However,  Garner  and 
Allard  found  that  many  plants  do  not  blossom  unless  the  duration  of  light  exposure 
is  short.  Voechtingi^-  found  that  a  decrease  m  light  intensity  reduced  the  number 
of  blossoms  and  eventually  prevented  flowering  altogether  in  some  plants,  while 
in  others  there  was  a  tendency  for  the  development  of  cleistogamous  flowers. 

Klebs""  found  that  when  blossoming  depends  on  the  intensity  of  illumination, 
red  hght  which  is  the  most  effective  in  photosynthesis  is  essential,  blue  light 
having  much  the  same  effect  as  darkness. 

Defoliation  previous  to  the  period  of  fruit  bud  differentiation  obviously 
interferes  with  carbohydrate  manufacture  and  the  recent  work  of  Harvey^"  shows 
that  this  is  reflected  in  the  chemical  composition  of  defoliated  apple  spurs  which 
contain  less  hydrolyzable  polysaccharides  and  total  carbohydrates  than  normal 
spurs.  This  is  particularly  important  in  connection  with  the  decreased  fruit 
bud  differentiation  observed  by  Harvey  on  defohated  fruit  spurs. 

In  Fruit  Spurs. — Hooker^"^  in  a  study  of  the  seasonal  changes  in  the 
chemical  composition  of  apple  spurs  of  certain  varieties  and  bearing 
habits  found  that,  when  there  was  a  relatively  low  total  nitrogen  content, 
starch  accumulation  occurred  while  fruit  buds  were  being  differentiated. 
When  there  was  a  relatively  high  total  nitrogen  content,  starch  accumula- 
tion did  not  occur  at  the  same  time,  though  it  followed  later,  and  the 
spurs  remained  vegetative  for  another  year.  These  conditions,  were 
found  in  spurs  showing  characteristically  different  behavior  regardless 
of  whether  spurs  of  only  one  or  of  several  different  bearing  habits  were 
found  on  the  same  tree  at  one  time.  Some  of  these  results,  shown 
graphically  in  Figs.  22  and  23,  emphasize  two  principles  involved  in  the 
development  of  the  fruitful  condition;  (1)  At  certain  critical  periods  in  the 
life  of  the  plant,  its  activities  are  directed  into  one  channel  or  another, 
depending  on  the  nature  of  the  conditions  affecting  its  equilibrium  at  that 
particular  time.     This  lends  weight  to  Kraus  and  Kraybill's  surmise 


184 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


that  "the  conditions  for  the  initiation  of  floral  primordia  and  even  bloom- 
ing are  probably  different  from  those  accompanying  fruit  setting."  In 
fact,  recent  work  by  Murneek^^  shows  that  the  conditions  favoring  fruit 


4 

\ 

A 

\ 

^1 

\ 

3 

\ 

\ 

0 

\ 

,^ 

\ 

\ 

2 

=-/ 

N1 

TRO^GEN 

\ 

^ 

^^^ 

^ 

^ 

\ 

/ 

PHOSPHORUS 

^ 

^ 

1 

\ 

/ 

\ 

1 

\ 

1 

0 

Fig.  22. — Nitrogen,  phosphorus  and  starch  contents  of  bearing  apple  spurs  compared. 
The  arrow  indicates  the  season  when  fruit  bud  differentiation  would  occur  in  non-bearing 
spurs.      {After  Eooker>^^) 

setting  in  apples  are  quite  different  from  those  determining  fruit  bud 
differentiation.  (2)  Different  parts  of  a  plant  may  act  quite  indepen- 
dently of  one  another,  depending  on  the  local  factors  affecting  them. 


/^ 

\, 

\ 

vy 

\ 

\ 

\ 

/' 

\ 

\ 

/ 

\ 

2 

\; 

\ 

y 

/, 

^o, 

V 

^ 

^ 

N^ 

VN. 

^ 

i 

'-rrr\ 

N 

^ 

1 

\ 

1 

1 

Nil 

\ 

0 

^ 

1 1 


Fig.  23. — Nitrogen,  phosphorus  and  starch  contents  of  non-bearing  apples  purs  compared. 
The  arrow  indicates  the  season  of  fruit  bud  differentiation.      (After  Hooker. ^'">) 

Influence  of  the  Nitrate  Supply. — When  the  nitrate  supply  was  varied 
in  Kraus  and  Kraj^bill's  experiments  the  amount  of  carbohydrate  utilization 
varied  with  it,  in  accordance  with  the  nutritive  relation  between  carbo- 


THE  INITIATION  OF  THE  REPRODUCTIVE  PROCESSES         185 

hydrates  and  nitrates.  Hence,  in  the  absence  of  any  other  Hmiting 
factors  for  vegetative  development,  the  balance  of  carbohydrate  manu- 
facture over  utilization  depends  on  the  nitrate  supply.  When  this  is 
kept  high,  though  carbohydrates  are  manufactured  in  large  quantities, 
they  are  immediately  utilized  for  vegetative  development  and  the  plants 
are  unfruitful  and  vigorously  vegetative.  If  the  nitrate  supply  is  reduced 
moderately,  carbohydrate  utilization  is  checked  and  there  is  opportunity 
for  carbohydrate  accumulation;  fruitfulness  follows.  To  be  sure  carbo- 
hydrate accumulation  occurs  when  the  nitrate  supply  is  still  further 
reduced,  but  here  the  situation  is  comphcated  because  nitrate  then 
becomes  a  limiting  factor  to  fruitfulness  by  inhibiting  such  vegetative 
development  as  appears  necessary  for  fruit  bud  differentiation.  Plants 
of  this  type  are  stunted  and  altogether  lacking  in  nitrate  nitrogen. 

Influence  of  the  Moisture  Supply. — Nitrate  supply  is  not  the  only  factor 
which  may  determine  the  balance  of  carbohydrate  manufacture  over 
utilization.  This  may  be  accomplished  also  by  a  decrease  in  any  other 
factor  involved  in  the  process  of  growth  and  development.  For  example, 
Kraus  and  Kraybill  report  that  "withholding  moisture  from  plants  grown 
under  conditions  of  relative  abundance  of  available  nitrogen  results  in 
much  the  same  condition  of  fruitfulness  and  carbohydrate  storage  as 
the  limiting  of  the  supply  of  available  nitrogen."  A  diminution  of  the 
water  supply  is  well  known  to  be  frequently  associated  with  fruitfulness. 
In  this  case,  as  in  that  of  nitrate  supply,  there  is  probably  a  limit  beyond 
which  a  further  reduction  of  the  water  supply  results  in  unfruitfulness 
and  stunted  growth. 

Influence  of  Other  Factors. — Klebs^^^  concluded  from  numerous  investi- 
gations that  a  reduction  in  the  supply  of  nutritive  salts  leads  to  the  fruit- 
ful condition  provided  there  be  adequate  facilities  for  photosynthesis 
and  hence  for  carbohydrate  accumulation.  Recent  work  of  Walster^^^ 
has  shown  that  heat  may  be  a  limiting  factor  to  vegetative  development 
as  well  as  water  or  any  of  the  essential  nutrient  and  food  materials  and 
that  diminished  heat,  even  with  a  high  nitrogen  supply,  leads  to  carbohy- 
drate accumulation  and  culm  formation  in  barley.  These  investigations 
indicate  that  any  environmental  factor  may  check  growth  and  lead  to 
carbohydrate  accumulation  and  that  fruitfulness  may  result  provided 
vegetative  development  is  not  seriously  retarded  or  altogether  stopped. 
It  is  shown  later  in  this  section  that  vigorous  vegetative  growth  is  not 
inimical  to  fruitfulness.  On  the  contrary,  the  facts  just  presented  indi- 
cate that  fruitfulness  and  vegetative  development  are  associated  functions. 

FRUIT-BUD  FORMATION 

Since  carbohydrate  accumulation  seems  associated  with  fruit  bud 
differentiation  and  the  conditions  for  carbohydrate  accumulation  change 
during  the  season,  it  is  evident  that  there  must  be  considerable  variation 


186  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

in  the  time  when  fruit  buds  are  formed.  A  knowledge  of  the  approximate 
time  when  their  differentiation  occurs  is  of  fundamental  importance, 
particularly  in  connection  with  possible  means  of  influencing  their  number 
by  cultural  treatment.  Furthermore,  the  stage  of  advancement  in  which 
the  fruit  buds  enter  the  winter  is  shown  elsewhere  to  have  an  important 
relation  to  winter  injury. 

For  many  years  flower  buds  of  the  ordinary  deciduous  fruit  trees 
have  been  known,  in  a  rather  indefinite  way,  to  have  their  inception  in 
the  summer  previous  to  their  opening;  more  exact  knowledge  is  compara- 
tively recent  and  is  even  now  rather  incomplete. 

Investigation  of  the  apple  has  been  more  extensive  than  is  the  case 
with  the  other  fruits;  there  is,  however,  enough  similarity  between  them 
to  permit  the  use  of  the  apple  as  the  type.  One  difference,  however, 
between  buds  of  apple  and  those  of  some  of  the  other  fruits,  pointed  out 
elsewhere,  should  be  borne  in  mind.  The  fruit  bud  of  the  apple  is,  with 
trivial  exceptions,  a  mixed  bud,  containing  leaves  and  blossoms;  in  the 
other  type,  as  the  peach,  fruit  buds  contain  no  leaves. 

Evidence  of  Differentiation. — The  growing  point  of  the  apple  shoot  or 
spur  presents  a  rounded  surface  surrounded  by  embryonic  leaves  and  it  is 
characterized  by  its  relatively  large  amount  of  meristematic  tissue. 
Sooner  or  later  its  aspect  changes,  taking  one  of  two  forms. 

In  one  case  the  change  consists  principally  in  the  greater  breadth  of 
the  surface  with  a  somewhat  smaller  degree  of  convexity  and  in  the 
absence  of  the  swellings  at  the  periphery  that  in  the  actively  growing 
shoot  precede  the  formation  of  a  rudimentary  leaf.  The  amount  of 
meristematic  tissue  becomes  relatively  smaller.  The  growing  point  is 
at  the  resting  stage;  surrounded  by  protective  scales  and  embryonic 
leaves,  it  constitutes  the  leaf  bud. 

In  the  alternative  case  the  growing  point  differentiates  into  structures 
that  form  the  essential  part  of  the  flower  or  fruit  bud.  The  first  evidence 
of  differentiation  in  this  direction  is  the  rapid  elevation  of  the  crown  or 
surface  of  the  growing  point  into  a  narrow  conical  form,  rounded  at  the 
apex,  with  the  fibro-vascular  connections  and  pith  areas  advancing 
concurrently.  In  the  axils  of  the  young  leaves  within  the  bud  appear 
other  protuberances  which  soon  become  blunt  at  the  top.  At  the  same 
time  other  leaf  primordia  develop  rapidly  higher  in  the  spiral  in  which 
they  appear  and  in  turn  younger  protuberances  (the  floral  primordia) 
appear  in  their  axils.  The  apical  protuberance,  destined  to  become  the 
central  (terminal)  flower  of  the  cluster,  is  differentiated  last;  however, 
when  it  does  take  shape  it  is  already  larger  than  those  previously  laid 
down.  It  soon  takes  and  thenceforth  maintains  the  lead  in  development 
over  the  other  flower  primordia  (see  Fig.  24). 

Whether  a  bud  which  has  entered  the  resting  stage  as  a  leaf  bud,  can, 
without  a  renewal  of  growth,  develop  into  a  fruit  bud  later  the  same 


THE  INITIATION  OF  THE  REPRODUCTIVE  PROCESSES         187 

season  is  a  matter  obviously  difficult  of  determination.  Indirect 
evidence,  however,  points  to  this  possibility  and  suggests  that  fruit  buds 
may  be  initiated  at  any  time  when  conditions  are  favorable.  It  is 
certain  that  a  spur  after  forming  a  leaf  bud  may  start  into  second  growth 
and  then  form  a  fruit  bud,  all  during  the  same  growing  season. 

Magness^^^  has  traced  the  development  of  axillary  buds.  He  finds  that: 
"axillary  buds  originate  very  close  to  the  tip  or  apex  of  rapidly  growing  shoots. 
As  the  shoot  elongates,  the  leaves  are  given  off  at  the  side  of  the  growing  point, 
and  the  young  bud  appears  first  as  simply  an  undifferentiated  mass  of  rapidly 
dividing  cells  in  the  axils  of  these  leaves  ...  no  primordia  were  found  de- 
veloping in  the  axils  of  leaves  that  were  not  fairly  well  formed. 

"The  buds  developed  very  rapidly  and  those  subtended  by  half-grown  leaves, 
1  to  2  inches  above  the  terminal,  were  well  differentiated,  with  a  growing  point  or 
apex,  and  bud  scales  being  rapidly  formed.  The  cells  of  the  growing  tip  were 
not  well  differentiated  and  this,  with  the  high  staining  reaction  of  this  region, 
indicated  that  much  growth  was  still  taking  place."  By  July  9  some  of  the  older 
axial  buds  had  nearly  reached  the  condition  in  which  they  would  pass  the  winter. 

Time  of  Differentiation.^ — Drinkard"^  reported  that  fruit  bud  differ- 
entiation in  the  Oldenburg  apple  occurred  about  June  20  in  Virginia. 
Goff^^  found  the  first  clear  evidence  in  the  Hoadley  apple  on  June  30  in 
Wisconsin.  Bradford'^  in  Oregon  found  similar  stages  during  the  first 
10  days  of  July,  though  resting  stages  of  leaf  buds  were  apparent  in  May. 
The  earliest  differentiation  observed  by  Kirby^"^  in  Iowa  was  about  the 
first  of  July. 

In  the  pear  it  was  observed  in  Virginia  in  samples  of  Kieffer  taken 
about  the  middle  of  July,  somewhat  later  than  the  initial  period  for  the 
apple. ^^  In  Wisconsin  evidence  was  found  in  the  Wilder  Early  on  July 
21.^^  Albert  first  found  differentiation  in  the  pear  early  in  August 
In  the  Champion  quince  Goff  found  embryonic  flowers  in  bud  examined, 
late  in  the  autumn,  but  did  not  determine  the  exact  period  of  their 
inception.  Alber't  found  differentiation  in  the  Japanese  quince  in  August. 
In  the  Luster  peach  initial  stages  of  flower  formation  were  observed  in 
Virginia  the  first  week  in  July;''^  Quaintance^^^  in  Georgia  found  no 
indication  of  differentiation  in  Demming's  September  peach  on  June  14, 
but  on  July  23  he  reported:  "the  embryo  flower  is  well  under  way 
and  the  calyx  lobes  are  quite  pronounced."  Apparently,  then,  the  initial 
stages  must  have  occurred  late  in  June.  Goff,^''  working  with  a 
Bokhara  peach,  considered  that  "flowers  began  to  form  about  the  middle 
of  September  the  past  season."  At  Davis,  California,  the  first  evidence 
of  differentiation  in  the  almond  has  been  reported  as  about  Aug.  18.  ^^^ 

The  plum  as  investigated  by  Drinkard  shows  some  variation  in  the 
time  of  initiation  of  fruit  buds.  Whitaker,  one  of  the  Wildgoose  group, 
gave  no  evidence  until  the  first  week  in  September;  "observations  on  sev- 
eral varieties  of  Japanese  plums  showed  that  the  initial  formation  of  fruit 


188  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

buds  occurred  during  the  second  week  in  July;  and  the  individual  fruit 
buds  within  the  cluster  were  clear  and  distinct  on  August  7th. "^^  In 
Wisconsin,  flower  formation  has  been  found  under  way  in  the  Aitken  plum 
on  Aug.  9  and  some  differentiation  in  the  Rollingstone  on  July  8  in  1899 
and  on  July  5  in  the  following  year.'^ 

In  the  Louis  Phillippe  cherry  of  the  Morello  group,  signs  of  differ- 
entiation have  been  noted  on  June  30  in  Virginia.  Goff,  working  with 
the  King's  Amarelle  cherry,  found  the  earhest  indications  of  flowers 
on  July  11^^  and  in  the  following  year  on  July  8.  At  Heidelberg, 
Germany,  blossom  primordia  of  the  sweet  cherry  were  visible  during 
July.«* 

Investigations  of  flower-bud  formation  in  the  small  fruits  were 
made  by  Goff.  In  the  strawberry  Sept.  20  was  the  date  of  the  first 
indication  of  flower  buds.''^ 

Differentiation  was  found  to  occur  in  the  Pomona  currant  about 
July  8  and  in  the  Black  Victoria  currant  about  Aug.  3.^^  In  the  Down- 
ing gooseberry  there  was  evidence  on  Aug.  30;  in  the  cranberry  no  clear 
signs  were  found  until  Sept.  16.  Less  definite  observations  were  made 
in  raspberries  and  blackberries;  nevertheless,  unquestionable  evidence 
shows  that  the  flowers  are  formed  the  year  previous  to  blossoming. 
"In  the  raspberry  and  blackberry,"  states  Goff,  "the  buds  that  form 
in  the  axils  of  the  leaves  of  the  young  shoots  contain  a  whole  branch  in 
embryo — often  several  nodes,  with  a  leaf  at  each  node.  The  bud  at 
the  apex  of  this  branch  and  the  axillary  buds  along  it,  if  they  form,  are 
flower-buds  .  .  .  embryo  flowers  in  those  buds  are  formed  the  season 
before  their  expansion,  at  least  in  part. " 

Fruit  bud  formation  in  the  grape  occurs  during  the  summer  previous 
to  blossoming.  A  single  bud  contains  in  embryo  a  shoot  with  blossom 
primordia.  General  observations  to  this  effect  are  recorded  by  Goff^'' 
and  Bioletti^^  but  no  precise  determination  of  the  time  is  available. 
Behrens^^  states  that  the  first  shoot  primordia  appear  concurrently  with 
the  first  swelling  of  the  buds  in  which  they  develop  (mid-June).  Since 
these  are  laid  down  continuously  through  the  summer  many  stages  are 
present  on  a  vine  at  any  one  time.  Subsequently  the  blossom  primordia 
appear.  The  buds  laid  down  late  in  the  season  are  likely  to  be  arrested 
in  their  development  before  the  formation  of  blossom  primordia  occurs. 
Behrens  emphasizes  the  importance  of  early  differentiation  in  securing 
a  crop  for  the  following  season. 

In  the  filbert  (Corylus  Avellana)  Albert^  found  signs  of  catkins  on 
June  10,  before  embyronic  leaves  were  laid  down;  female  blossoms  were 
not  found  until  early  in  September.  In  the  beech  he  was  unable  to 
find  blossom  buds  until  the  beginning  of  leaf  fall,  but  since  the  pollen 
mother  cells  in  the  anthers  had  already  formed,  differentiation  must 
have  occurred  much  earlier. 


THE  INITIATION  OF  THE  REPRODUCTIVE  PROCESSES 


189 


In  Relation  to  Position. — Not  all  fruit  buds  are  differentiated  simul- 
taneously, even  on  the  same  tree.  Investigations  by  Goff"^  convinced 
him  that  in  the  apple  and  pear  fruit-bud  formation  may  occur  after  the 


Fig.  24. — Stages  in  fruit  bud  development  of  the  Yellow  Newtown  apple.  Above,  to 
the  left  Sept.  10,  to  the  right  Nov.  25;  below,  to  the  left  Feb.  14,  to  the  right  Mar.  6. 
(After  Bradford.^') 


first  of  September;  he  suggested  as  alternatives  either  (1)  two  periods 
of  flower  formation  or  (2)  a  continual  differentiation  through  the  season. 
Bradford,  working  with  the  Yellow  Newton  apple,  reports  least  variation 
in  spurs  which  have  borne  previously  but  are  not  bearing  in  the  current 


190  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

season  (see  Fig.  24) ;  terminal  fruit  buds  on  long  shoots  obviously  must  be 
differentiated  at  a  later  period  than  is  known  to  characterize  formation 
on  spurs.  Considerable  variation  in  the  time  of  differentiation  occurs 
also  in  young  spurs  which  have  never  before  formed  fruit  buds.  Even  in 
bearing  spurs,  when  they  form  fruit  buds,  the  formation  may  occur  from 
early  July  to  late  August.  Spurs  which  had  blossomed  during  the  current 
season  but  failed  to  set  fruit  varied  still  more;  some  of  the  earliest 
differentiation  observed  was  found  in  spurs  of  this  class  and  later  differ- 
ention  also  occurred. 

Magness^^T  [^  q^  careful  study  of  axial  buds  found  resting  stages  of 
leaf  buds  in  several  varieties  as  early  as  July  9  and  early  in  September 
he  recognized  differentiation  into  flower  buds.  Some  of  his  preparations 
taken  in  December  suggest  an  initial  differentiation  into  fruit  buds, 
though  he  evidently  did  not  regard  them  as  such.  In  the  Tetofski  apple 
he  considered  some  differentiation  to  have  occurred  about  the  first  of 
August.  He  states  that  a  spur  bud  of  July  23  showed  as  much  develop- 
i^ent  as  the  most  advanced  axillary  buds  of  Sept.  2.  In  the  investi- 
gations of  the  following  year  the  "main  period  of  axillary  fruit-bud 
formation  in  the  varieties  studied  began  after  August  1,  and  a  great 
many  buds  were  apparently  being  differentiated  on  September  8.  This 
was  fully  one  month  later  than  spur  buds  on  the  same  trees." 

Direct  comparisons  of  the  time  of  differentiation  in  buds  of  stone 
fruits  in  different  positions  are  not  available.  Roberts, ^^^  however, 
finds  in  September  a  difference  in  the  development  of  buds  on  sour 
cherries  according  to  their  positions  on  the  4-  or  5-inch  shoot.  This 
difference  suggests  that  flower  formation  is  initiated  first  both  in  the  basal 
and  in  terminal  regions.  It  is  probable  that  a  similar  condition  occurs 
in  the  peach. 

Goff'''^  found  little  or  no  difference  in  the  comparative  develop- 
ment of  flower  buds  in  rooted  runners  and  parent  plants  in  the 
strawberry. 

Varietal  Differences. — Bradford"-^  found  considerable  difference  be- 
tween varieties  of  apple  in  the  stage  of  development  attained  early  in 
August,  indicating  a  lack  of  uniformity  in  the  time  of  differentiation. 
Of  the  varieties  observed,  Stark,  Red  Astrachan  and  Oldenburg  seemed 
farther  advanced  than  Jonathan,  Northern  Spy  and  Grimes.  The 
season  of  ripening  of  the  fruit  appears  to  make  little  difference  in  the 
time  of  differentiation;  there  appears  to  be,  however,  some  correspond- 
ence, though  not  absolute,  between  the  order  of  blossoming  and  the  order 
of  differentiation.  Magness^^T  found  White  Pearmain,  Tetofski  and 
Yellow  Transparent  noticeably  advanced  in  development  in  early  July 
as  compared  with  Lady  and  Jonathan. 

Goff''^  found  considerable  difference  between  varieties  in  the  time 
of  fruit-bud  formation,  some  forming  fruit  buds  before  Aug.  1  while  some 


THE  INITIATION  OF  THE  REPRODUCTIVE  PROCESSES         191 

were  considered  to  form  none  until  after  the  first  of  September.     Differ- 
ences between  varieties  of  plums  have  been  mentioned  earlier. 

Differences  Induced  by  Cultural  Treatment. — Kirby^''^  notes  an  earlier 
differentiation  of  fruit  buds  in  apples  growing  in  sod  than  in  the  same 
varieties  in  cultivated  soil.     Still  finer  distinctions  were  noted. 

"The  earliest  time,"  he  states,  "at  which  flower  buds  were  formed  occurred 
on  clover  sod,  with  a  low  percentage  of  soil  moisture.  Flower  buds  formed 
earUer  on  a  clover  sod  than  on  a  blue  grass  sod  having  slightly  less  soil  moisture. 
On  the  other  hand,  flower  buds  formed  earlier  on  a  blue  grass  sod  than  on  a  clover 
sod  having  about  2.5  per  cent,  more  soil  moisture.  These  facts  indicate  two 
things ;  first,  that  the  addition  of  nitrates  in  the  clover  sod  causes  the  flower  buds 
to  form  earlier;  and  second,  that  the  amount  of  soil  moisture  is  a  very  important 
if  not  the  chief  external  factor  in  determining  the  time  at  which  flower  buds  form. 

"The  formation  of  flower  buds  began  about  the  first  of  July  on  the  plots 
where  it  occurred  earliest  and  extended  until  the  middle  of  September  on  the 
plots  where  it  occurred  latest,  thus  occupying  a  period  of  about  2>2  months. 
The  time  occupied  by  each  tree  in  forming  flower  buds  was  about  4  weeks." 

The  time  of  differentiation  in  the  Baldwin  apple  in  New  Hampshire 
has  been  found  somewhat  variable,  suggesting  the  effect  of  influences 
proceeding  directly  or  indirectly  from  weather  conditions. ^^ 

Goff^''  supplied  water  to  a  9-year  old  Gideon  apple  tree  in  a  dry  season. 
Comparison  on  Aug.  9  with  a  similar  unwatered  tree  showed  very  little 
difference  in  the  stage  of  development  reached  at  that  time,  though  buds 
on  the  non-watered  tree  were  somewhat  more  advanced. 

In  the  sour  cherry  very  strongly  growing  shoots  and  shoots  partly 
defoliated  by  shot-hole  fungus  were  retarded  in  their  development.  ^^^ 
Buds  on  younger  trees  were  less  advanced  than  those  on  older  trees  of 
the  same  variety.  Since  these  studies  were  made  at  the  approach  of 
winter  they  do  not  furnish  conclusive  evidence  as  to  the  time  of  differen- 
tiation.    However,  they  harmonize  with  the  available  direct  evidence. 

Abnormalities. — Finally,  the  occurrence  of  the  so-called  second 
bloom  should  be  noted.  Paddock  and  Whipple^^^  mention  a  case  of 
this  kind.  Similar  teratological  variations  reported  by  Daniel  were 
attributed  by  him  to  excessive  pruning.  This  occurrence  has  been 
attributed  at  times  to  late  frosts  which  destroyed  the  first  blossoms  and 
induced  the  formation  of  another  set.  This  may  be  a  correct  explanation 
in  some  instances.  The  occurrence  of  blossoms  on  the  vegetative  shoots 
of  several  spurs  bearing  fruit  in  normal  position  was  noted  in  an  Olden- 
burg apple  at  Columbia,  Mo.,  in  1920;  the  following  year  the  same  tree 
showed  this  phenomenon  in  about  20  per  cent,  of  its  spurs  before  any 
injurious  frost  occurred.  Whether  these  buds  were  differentiated  the 
preceding  season  cannot  be  stated  positively.  However,  in  the  Rome 
Beauty  apple  vegetative  shoots  from  fruiting  spurs  were  observed  to 
grow  to  a  length  of  4  to  6  inches,  forming  6  or  7  leaves  and  then — 
still  early  in  the  season — to  open  solitary  blossoms.     In  this  case  differ- 


192  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

entiation  undoubtedly  occurred  in  the  spring.  Hand  pollination  in  some 
cases  resulted  in  the  formation  of  fruits  with  seeds  of  normal  appearance 
and  in  Oldenburg  without  such  assistance  a  considerable  proportion 
of  the  crop  actually  harvested  developed  from  secondary  bloom. 

Apple  trees  in  tropical  climates,  though  they  blossom  little,  seem  not 
to  be  restricted  in  the  time  of  fruit-bud  formation. 

The  conclusion  seems  warranted  that  a  fruit  bud  may  be  formed 
at  any  time,  though  ordinarily  the  period  is  rather  restricted.  The 
period  evidently  can  be  varied  somewhat  by  cultural  treatments,  includ- 
ing perhaps  any  practice  that  modifies  the  rate  of  growth.  In  general 
the  earlier  the  period  of  differentiation,  the  greater  the  number  of  fruit 
buds  finally  formed,  but  as  shown  elsewhere,  with  some  qualifications, 
the  less  hardy  those  buds  are. 

Winter  Stages. — Kraus^^*  has  described  in  detail  the  development  of 
the  individual  flower  within  the  bud.  The  sepals  are  differentiated  first, 
followed  closely  by  the  primordia  of  the  petals.  Either  simultaneously 
with,  or  directly  after,  their  appearance  those  of  the  stamens  are  laid 
down;  after  these  come  the  primordia  of  the  carpels.  The  ovules  do  not 
appear  until  the  resumption  of  growth  in  the  spring. 

During  November  and  December  in  Virginia,  Drinkard^^  found 
little  development  of  the  gross  parts  of  the  apple  flower  but  noted  some 
cytological  changes.  "During  December,"  he  states,  "the  pollen 
mother  cells  developed  large,  prominent  nuclei.  .  .  .  Nearly  all  changes 
which  occurred  during  the  month  of  January  took  place  in  the  stamens. 
...  On  February  19,  there  was  some  indication  of  renewed  develop- 
ment in  the  anthers;  these  had  enlarged  appreciably  on  February  24. 
.  .  .  Early  in  March  there  was  a  beginning  of  development  of  ovules 
in  the  cells  of  the  ovary.  These  became  very  distinct  by  March  22.  At 
the  same  time  tetrad  formation  was  going  on  in  the  pollen  mother  cells." 

Drinkard  found  some  development  during  the  winter  in  buds  of  pear 
also.  In  the  peach,  growth  during  winter  seemed  more  active.  The  ovule 
appeared  late  in  December  and  tetrad  formation  in  the  pollen  mother  cells 
late  in  January,  in  both  instances  considerably  in  advance  of  the  apple. 
Similarly  the  plum  was  found  to  show  more  or  less  development,  practi- 
cally throughout  the  winter.  These  observations  are  of  interest  in  con- 
nection with  the  differences  in  hardiness  of  fruit  buds  discussed  elsewhere. 

However,  it  has  been  reported  that  in  New  York  fruit  buds  do  not 
develop  from  the  middle  of  November  until  about  the  first  of  March^o^ 
■  and  in  Wisconsin  no  evidences  of  activity  were  found  from  the  beginning 
of  freezing  weather  until  after  the  middle  of  March. ^^  In  fact  it  was 
stated  that  there  was  no  change  in  pear  flowers  from  Dec.  1  to  Mar.  30.^^ 
Albert  reports  pear  blossoms  to  be  unchanged  until  March,  though  he 
records  development  in  the  pistils  of  the  filbert  during  November  and 
December.     In  Japanese  quince  he  found  that  development  is  arrested 


THE  INITIATION  OF  THE  REPRODUCTIVE  PROCESSES         193 

only  during  cold  weather  and  is  resumed  whenever  temperatures  permit. 
Many  of  these  blossoms  are  killed  by  cold. 

Magness^"  noted  a  difference  in  the  stage  of  development  of  buds  on 
spurs  in  successive  years.  Buds  of  the  Tetofski  apple  in  November, 
1914,  showed  ovules  developed,  while  in  December,  1915,  they  had  not 
reached  that  stage. 

"The  blooming  season  during  the  spring  of  1915  was  fully  one  week  earlier," 
he  states,  "than  that  of  1916.  It  is  quite  probable  that  factors  operating  during 
the  late  summer  and  fall  to  hasten  or  retard  flower  development,  as  well  as  factors 
operating  during  the  spring,  materially  influence  the  time  of  blossoming  in  our 
orchard  fruits."  This  statement  is  of  particular  interest  when  correlated  with 
Sandsten's  work,  discussed  under  Temperature  Relations. 

Summary. — The  available  data  do  not  permit  a  definite  statement  of 
the  exact  cause  or  causes  of  fruit  bud  differentiation  or  an  exact  de- 
cription  of  the  internal  nutritive  conditions  associated  with  fruitfulness 
and  unfruitfulness.  However,  there  must  be  at  least  two  antecedents 
to  an  initiation  of  the  reproductive  processes:  (1)  There  must  be  an 
excess  of  carbohydrates  above  the  amount  required  for  vegetative 
development.  The  rate  of  manufacture  must  exceed  the  rate  of  utili- 
zation. (2)  There  must  not  be  any  limiting  factor  that  entirely  stops 
vegetative  growth  which  must  continue  within  the  bud  even  though  there 
be  no  new  shoots  and  leaves  formed  or  even  no  visible  indication  of  an 
increase  in  the  size  of  the  buds  that  are  differentiating  flower  parts.  In 
Jthe  orchard  the  supply  of  available  nitrogen  is  probably  the  most  common 
limiting  factor.  If  nitrogen  is  present  in  large  amounts  it  forces  the  rapid 
utilization  of  carbohydrates  so  that  their  accumulation  cannot  occur.  If 
it  is  very  limited  in  amount,  growth  is  practically  stopped  before  fruit 
bud  differentiation  can  take  place.  Carbohydrate  accumulation  may 
not  in  itself  be  the  cause  of  the  fruitful  condition  in  the  plant  as  a  whole 
or  in  its  individual  parts.  It  may  simply  be  another  result  of  the  same 
factors  that  lead  to  fruitfulness;  at  least,  however,  the  two  are  associated. 

In  practically  all  the  deciduous  fruits  growing  in  temperate  climates 
fruit  bud  differentiation  occurs  during  the  summer  or  fall  previous  to  the 
opening  of  the  buds.  Every  bud  that  is  formed  may  be  considered  a 
potential  fruit  bud,  but  practically  differentiation  takes  place  only  when 
suitable  nutritive  conditions  are  provided.  Ordinarily  each  bud  develops 
to  a  certain  point  and  then  comes  to  a  comparative  rest.  Later  develop- 
ment is  as  a  vegetative  bud  or  a  flower  bud,  depending  on  whether  con- 
ditions do  or  do  not  favor  differentiation  of  flower  parts  in  the  slow  growth 
that  takes  place  during  the  period  of  comparative  rest.  The  exact  time 
of  differentiation  varies  considerably  with  variety,  seasonal  conditions, 
moisture  supply,  method  of  culture,  position  on  the  plant  and  other 
factors.  In  cold  climates  there  are  practically  no  changes  within  the  bud 
during  the  winter. 


CHAPTER  XI 
SURPLUSES  AND  DEFICIENCIES 

Though  much  has  been  written  on  the  function  of  individual  mineral 
constituents,  it  is  questionable  whether  definite  roles  can  be  assigned 
to  them,  except  in  so  far  as  they  enter  into  the  composition  of  specific 
organic  compounds  that  have  known  functions.  Thus  magnesium  is  a 
component  of  the  chlorophyll  molecule,  which  is  essential  for  photosyn- 
thesis. It  is  important,  nevertheless,  to  know  the  effects  attending  a 
surplus  or  a  deficiency  of  one  or  more  mineral  elements,  so  that  the  symp- 
toms may  be  recognized  and  the  condition  corrected.  However,  patho- 
logical conditions  found  to  follow  an  excess  or  deficiency  of  any  one 
element  do  not  necessarily  indicate  a  direct  relation  of  the  element  to 
the  symptoms.  Thus,  though  a  deficiency  of  iron  is  known  to  produce 
chlorosis,  a  disordered  condition  in  which  chlorophyll  does  not  develop, 
iron  does  not  occur  in  the  chlorophyll  molecule. 

From  the  considerations  in  the  previous  chapters,  it  follows  that 
either  a  surplus  or  a  deficiency  of  any  soil  element  may  affect  the  plant 
by  disturbing  the  balance  between  its  various  constituents.  A  defi- 
ciency of  an  element  may  also  affect  the  plant  when  that  element  is  a 
limiting  factor  of  growth.  In  all  cases,  a  surplus  or  a  deficiency  must  be 
understood  to  mean  an  amount  greater  or  less  than  that  which  is  utilized 
along  with  the  other  elements  of  the  soil.  The  effect  of  a  surplus  of  any 
essential  soil  constituent  must  be  upon  the  balance  or  equilibrium  of  the 
plant.  There  may  be  no  effect,  since  the  plant  may  adjust  itself  to  a 
surplus  which  is  merely  tolerated.  There  is  much  evidence  that  the 
quantities  of  potassium  and  calcium  in  plant  tissues  are  often  much  in 
excess  of  the  amounts  used  in  metabolism.  The  same  undoubtedly 
holds  for  other  essential  and  many  non-essential  elements  such  as  sodium, 
chlorine,  aluminum  and  sihcon.  On  the  other  hand,  distinct  pathological 
conditions  may  ensue  which  lead  eventually  to  the  death  of  the  plant. 
Likewise  elements  which  are  not  essential  to  the  nutrition  of  the  plant 
may  be  tolerated  or  they  may  produce  disturbances,  the  effects  of  which 
may  be  either  to  stimulate  assimilation  or  to  induce  pathological  con- 
ditions and  eventually  death.  As  a  general  physiological  theorem,  it 
may  be  stated  that  any  substance  which  is  toxic  in  certain  amounts  is 
stimulating  in  smaller  amounts. 

SURPLUSES 

The  evidences  for  the  existence  of  pathological  conditions  due  to  the 
absorption  of  a  surplus  of  some  soil  nutrient  are  practically  limited  to  the 
cases  of  nitrogen  and  magnesium. 

194 


SURPLUSES  AND  DEFICIENCIES  195 

Nitrogen. — The  results  of  an  excess  of  nitrogen  usually  appear  the 
year  following  the  actual  surplus  nitrogen  absorption.  They  are  shown^*"^ 
in  trees  by  a  tendenc}^  in  the  fruit  to  physiological  decay.  Dieback, 
or  exanthema,  and  gummosis  of  citrus  trees  also  are  attributed  to  a 
surplus  of  nitrogen. '^'■'^  This  causes  a  diseased  condition  in  the  growing 
tissues  of  the  tree  characterized  primarily  by  gum  pockets,  stained 
terminal  branches,  "ammoniated"  fruits,  bark  excrescences  and  multiple 
buds.  The  secondary  symptoms  are  an  unusually  deep  green  color  of 
the  foliage,  distorted  growth  of  the  terminal  branches,  frenching  of  the 
foliage  and  thick  coarse  leaves  shaped  like  those  of  the  peach.  Mineral 
sources  of  nitrogen,  even  in  great  quantities,  are  not  known  to  produce 
dieback  though  they  may  accentuate  the  symptoms  in  trees  already 
affected,  ^^  but  organic  fertilizers  containing  nitrogen  often  lead  to  its 
development  when  they  are  appHed  in  large  amounts. 

Magnesium. — The  poisonous  action  of  an  excess  of  magnesium 
absorbed  by  the  plant  is  attended  by  a  browning  of  the  roots  and  of 
vessels  in  the  wood,  cessation  of  growth  in  the  roots  and  eventually  death 
of  the  root  hairs,  the  entire  roots  and  leaves.  These  toxic  effects  may  be 
counteracted  in  large  part  by  calcium  through  its  antagonistic  action  on 
magnesium,  previously  discussed.  It  should  be  pointed  out  that  toxic 
effects  similar  to  those  following  an  excess  of  magnesium  have  been 
observed  to  develop  from  oxalic  acid  and  that  the  toxic  effects  of  other 
salts  and  salt  mixtures,  such  as  potassium  nitrate  with  potassium 
phosphate,  may  be  corrected  by  calcium. 

Copper. — Of  the  effects  of  non-essential  elements,  those  of  copper  are 
among  the  most  striking.  Copper  salts  are  poisonous  even  in  exceed- 
ingly small  concentrations.  Water  distilled  in  copper  receptacles  is 
frequently  toxic.  Coupin''^  found  that  the  lethal  dose  for  grains  grown 
in  water  culture  was  for  each  100  cubic  centimeters  of  nutrient  solution, 
0.0049  gram  copper  bromide;  0.005  copper  chloride;  0.0056  copper 
sulfate;  0.0057  copper  acetate  and  0.006  copper  nitrate.  Copper  salts 
absorbed  by  the  roots  of  the  grape  are  likely  to  stop  root  growth.  On  the 
other  hand,  the  stimulating  effect  of  a  mixture  of  copper  sulfate  and  lime 
sprayed  on  leaves  is  well  known.  Leaf  development  is  stimulated,  the 
chlorophyll  content  increased,  the  palisade  cells  become  longer  and  nar- 
rower and  the  spongy  parenchyma  has  smaller  intercellular  spaces.^" 
Without  doubt  the  amounts  of  copper  absorbed  by  the  sprayed  leaves  are 
less  than  those  which  produce  toxic  effects  when  absorbed  by  the  roots. 
Ewert,^^  however,  has  demonstrated  that  concentrations  of  1  to  100,000,- 
000  of  copper  sulfate  are  toxic  to  the  pulp  cells  of  the  apple  and  that 
minute  quantities  entering  through  the  stomata  after  spraying  or  taken 
up  by  the  roots  may  result  in  one  of  the  forms  of  bitter  pit.  If  the  con- 
tention^^^  that  copper  is  an  essential  nutrient  be  correct,  then  the  observed 
effects  may  be  the  result  of  counteracting  a  limiting  factor  of  assimilation. 


196  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Arsenic. — Arsenic  is  another  mineral  toxic  to  plants  in  exceedingly 
small  amounts.  In  many  of  the  higher  plants  exposure  to  a  concentra- 
tion of  1  part  in  1,000,000  is  sufficient  to  inhibit  growth.  ^^^  When  arsenic 
is  absorbed  by  the  roots,  they  show  its  effects  first. 

The  toxic  effects  of  arsenic  on  fruit  trees  are  described  in  an  article  in  the 
Horticulturist. ^°2  "When  a  little  arsenic  is  introduced  into  the  circulation  of 
a  fruit  tree  at  that  season  (early  spring)  it  first  discolors  the  sap  vessels  of  the 
inner  bark,  then  the  leaves  suddenly  flag,  and  droop;  the  branch  shrivels  and 
turns  black;  and  finally  if  the  dose  is  large  enough,  the  whole  tree  dies."  Stimu- 
lating effects  from  arsenic  have  been  observed,  presumably  when  absorption  was 
restricted  to  amounts  smaller  than  that  indicated  above  as  toxic. 

The  question  of  the  toxic  action  of  arsenic  is  one  of  much  interest 
since  nearly  all  deciduous  orchard  fruits  require  one  or  more  applications 
of  arsenical  sprays  each  year.  In  old  bearing  orchards  the  total  arsenic 
used  per  acre  each  year  is  Hkely  to  be  as  much  as  4  pounds,  figured  as 
arsenic  trioxide.  Though  applied  directly  to  the  foliage  and  fruit,  most 
of  it  reaches  the  ground  in  the  course  of  the  season.  It  is  generally 
applied  in  some  very  insoluble  and  chemically  inactive  form,  such  as 
arsenate  of  lead.  However,  there  is  a  considerable  accumulation,  espe- 
cially in  the  surface  soil,  as  spraying  is  continued.  This  has  led  to  con- 
siderable uneasiness  among  growers  and  much  injury  has  been  reported 
to  be  due  to  these  accumulations  in  some  of  the  irrigated  sections.  The 
injury  has  taken  the  form  of  collar  and  root  rot  and  in  addition  it  has 
often  been  followed  by  premature  ripening  of  the  fruit  and  wood  in  the 
fall  and  the  death  of  the  tree  the  following  year.  However,  it  is  only  in 
irrigated  sections  and  in  soils  with  a  rather  high  alkali  content  that  this 
trouble  has  been  encountered.  This  suggests  that  the  injury  is  attribu- 
table to  the  action  of  various  alkali  salts  reacting  with  the  arsenic  to  make 
it  soluble,  to  the  combined  action  of  alkali  salts  and  arsenic,  or  possibly 
to  alkali  salts  alone,  since  similar  injuries  are  known  to  result  from  alkali 
poisoning.  Results  with  Ben  Davis  apple  trees  sprayed  in  one  season  with 
as  much  arsenic  as  ordinarily  would  be  apphed  in  10  to  40  years  and  under 
conditions  where  soil  alkali  was  not  a  factor,  have  led  to  the  conclusion 
that  such  arsenical  poisoning  as  has  been  reported  from  certain  sections 
is  not  attributable  to  the  arsenic.^  Some  of  these  applications  were  so 
heavy  that  the  trees  not  only  remained  whitened  all  summer,  but  the 
"ground  under  the  entire  head  of  the  tree  was  so  saturated  with  the 
arsenic  as  to  appear  moldy  white  to  a  depth  of  3  or  4  inches."  No  injury 
appeared  in  the  trees  or  even  in  the  vegetation  (including  strawberries, 
alfalfa  and  a  number  of  weeds)  under  some  of  them.  This  makes  it 
evident  that  little  is  to  be  feared  from  the  toxic  effect  of  the  arsenic  used 
in  spraying  unless  the  soil  has  a  fairly  high  alkali  content  and  then  the 
problem  is  one  of  dealing  with  the  alkali  rather  than  with  the  arsenic. 
Arsenic  is,  however,  a  contributing  factor.     Ewert^^  believes  that  there  is 


SURPLUSES  AND  DEFICIENCIES  197 

possibility  of  the  absorption  through  the  stomata  and  cuticle  of  the  fruit 
of  quantities  sufficient  to  cause  local  poisoning  in  the  apple,  giving  rise 
to  the  disorder  known  as  bitter  pit. 

Manganese. — The  relation  of  an  excess  of  manganese  to  iron  deficit 
and  the  method  of  curing  the  diseased  condition  have  been  discussed. 
In  excess,  this  element  produces  interesting  symptoms,  illustrated  by 
pineapples  grown  on  manganese  soils. 

The  root  system  is  reduced  by  the  death  of  a  large  percentage  of  the  fine 
branched  rootlets  some  months  after  their  formation.  The  roots  that  remain 
alive  have  a  superabundance  of  root  hairs,  almost  every  epidermal  cell  elongating 
into  one,  and  also  a  blunt  growing  tip,  about  half  as  large  as  a  lead  pencil, 
frequently  swollen  into  an  enlarged  fleshy  end.  The  formation  of  these 
enlargements  seems  to  mark  the  end  of  growth  and  death  soon  follows.  The 
leaf  has  an  irregular  surface  due  to  shrinkage  from  loss  of  water,  producing 
prominences  which  become  dark  brown.  The  cells  have  brown  walls  and 
in  some  cases  the  protoplasm  eventually  disintegrates.  The  green  cells  thus 
lose  their  color,  become  plasmolized  and  in  some  cases  the  nuclei  turn  brown. 
Here  also  the  protoplasm  loses  its  granular  structure  and  disintegrates.  As  a 
result  of  the  lack  of  chlorophyll,  the  leaves  contain  limited  amounts  of  starch, 
but  at  the  base  of  the  leaves,  in  the  stalks  and  roots,  starch  is  abundant,  having 
been  stored  there  before  the  decomposition  of  the  chlorophyll.  Frequently  no 
fruit  develops,  but  that  which  does  is  reddish  pink,  without  a  trace  of  green, 
undersized  and  excessively  acid.>°^ 

Apparently  manganese  poisoning  is  rare  in  deciduous  fruits.  In 
very  dilute  amounts  manganese  has  a  stimulating  effect. ^^ 

Other  Elements. — Compounds  of  many  other  elements  such  as  lead, 
mercury,  zinc,  boron^^  and  silver  are  toxic  in  certain  concentrations,  but 
toxic  effects  from  them  are  rare.  However,  these  materials  are  known 
occasionally  to  be  absorbed  in  considerable  quantities — zinc  for  example 
up  to  13  per  cent,  of  the  ash,  mercury  and  copper  up  to  1  per  cent.®^ 
Ewert^^  has  shown  that  extremely  minute  quantities  of  these,  in  con- 
centrations varying  from  1  in  1,000,000  to  1  in  1,000,000,000,  may 
cause  local  browning  in  the  tissues  of  the  fruit  of  the  apple  and  induce  the 
condition  known  as  bitter  pit. 

Mention  may  be  made  here  of  certain  toxic  gases  such  as  hydrogen 
sulfide,  sulfur  dioxide,  hydrogen  cyanide  and  chlorine.  Sulfur  dioxide 
injury  is  of  considerable  practical  importance  because  the  damage  done 
to  vegetation  by  smelter  fumes  is  due  largely  to  this  compound. 

The  bulk  of  the  evidence  on  the  toxicity  of  inorganic  mineral  soil 
constituents  that  has  been  discussed,  suggests  that  the  effects  are  largely 
local  in  the  plant.  Amounts  small  enough  to  be  stimulating  are  unques- 
tionably absorbed  by  the  roots,  or  in  the  case  of  spraying,  by  the  leaves, 
but  amounts  large  enough  to  poison  the  plant  seem  to  induce  injury 
chiefly  by  affecting  the  absorbing  organs.     Hence  cessation  of  growth 


198  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

and  eventually  death  of  the  roots  are  the  primary  symptoms.  Dis- 
orders proceeding  from  the  causes  just  outlined  should  be  distinguished 
from  the  toxic  effects  produced  by  organic  compounds  or  by  excessive 
soil  concentrations,  discussed  previously. 

DEFICIENCIES 

The  lack  of  a  sufficient  amount  of  any  essential  soil  constituent  may 
lead  to  the  development  of  distinct  pathological  conditions,  or  it  may 
result  simply  in  checking  vegetative  development  and  fruit  production 
without  producing  obvious  pathological  symptoms.  The  use  of  fertil- 
izers for  correcting  both  of  these  conditions  is  discussed  in  the  two 
following  chapters  in  which  particular  emphasis  is  accorded  the  correc- 
tion of  conditions  interfering  with  fruit  production  on  a  commercial 
scale.  The  discussion  immediately  following  concerns  the  more  impor- 
tant pathological  symptoms  which  are  associated  with  the  presence  of 
unduly  small  amounts  or  with  the  complete  exhaustion  of  essential 
mineral  elements. 

Nitrogen. — A  deficiency  of  nitrogen  may  become  evident  in  several 
different  ways.  The  plant  may  be  dwarfed,  though  it  develops  com- 
pletely and  produces  flowers,  fruits  and  seeds.  As  a  rule,  however,  the 
leaves  are  pale  green  because  of  the  relatively  small  amounts  of  chloro- 
phyll and  the  development  of  the  mature  fruit  is  affected  in  one  way 
or  another.  There  may  be  an  incomplete  development  of  the  sexual 
organs,  and  consequent  unfruitfulness;^^°  in  case  fruits  develop  they  may 
be  seedless,  as  in  apples,  pears  and  grapes, ^^^  or  the  fruit  may  develop 
somewhat  but  drop  prematurely.  This  is  a  common  result  of  nitrogen 
deficiency  in  apples  and  pears.  The  latter  sometimes  show  excessive 
thorn  development  in  connection  with  a  lack  of  nitrogen. ^'^^ 

Phosphorus  and  Potassium. — A  deficiency  of  phosphorus  appears 
to  produce  no  characteristic  symptoms.  Chlorophyll  development  is 
not  affected,  but  the  plant  does  not  increase  in  dry  weight. 

A  deficiency  of  potassium^''"  is  usuallj^  associated  with  a  scarcity 
of  carbohydrate  reserves.  In  trees,  the  terminal  shoots  show  weak 
development  and  eventually  dry  out,  or  shoot  formation  may  be 
suppressed  wholly.  Plants  suffering  from  a  lack  of  potassium  often 
maintain  a  health}'-  appearance  longer  than  those  lacking  nitrogen  or 
phosphorus.  Whatever  potassium  is  available  apparently  is  used  first  for 
vegetative  growth  and  development  and,  if  there  is  no  residuum,  the  plant 
does  not  blossom.  Eventually  the  leaf  blade  becomes  yellow  on  the 
edges  and  between  the  veins,  then  brown  and  finally  white,  while  the 
veins  and  petiole  remain  green.  This  condition  is  known  as  a  frenching 
of  the  foliage.  A  potassium  deficiency  renders  the  roots  susceptible  to 
rotting  and  the  plant  eventually  dies.  When  nitrogen  or  phosphorus  is 
deficient,  plants  are  likely  to  remain  alive  longer  in  a  stunted  condition. 


SURPLUSES  AND  DEFICIENCIES  199 

Sulphur. — As  a  result  of  sulphur  deficiency,  cell  division  is  retarded 
and  fruit  development  is  suppressed, '^^^  but  the  plant  is  able  to  develop 
vegetatively  to  a  limited  extent. 

Iron. — A  lack  of  iron  produces  the  well-known  condition  of  chlorosis 
or  yellows.  This  is  not  characteristic  solely  of  iron  want,  for  it  may 
result  eventually  from  a  lack  of  either  nitrogen  or  magnesium,  but  the 
effects  of  iron  deficiency  in  producing  chlorosis  are  more  rapid  than 
those  of  nitrogen  insufficiency  and  consequently  more  striking.  When 
iron  is  deficient,  developing  leaves  are  at  first  able  to  avail  themselves 
of  iron  in  older  tissues.  Later  the  new  leaves  are  green  only  at  the  tips 
and  eventually  the  newly  developed  leaves  are  entirely  yellow.  Chloro- 
plasts  develop  in  them,  but  they  contain  no  chlorophyll.  Recent 
investigation^*^  has  shown  that  organic  compounds  containing  the  pyrrol 
ring,  which  appears  in  the  structure  of  chlorophyll,  correct  the  condition 
of  chlorosis  produced  by  iron  want,  suggesting  that  iron  may  have 
something  to  do  with  the  formation  of  this  ring.  However,  since  iron  is 
just  as  essential  for  fungi  and  other  parasitic  plants  which  have  no  chloro- 
phyll as  for  green  plants,  its  importance  cannot  be  limited  to  the  part 
it  apparently  plays  in  the  synthesis  of  the  pyrrol  ring. 

Magnesium  and  Calcium. — A  deficiency  of  magnesium^"  reduces 
fruit  formation  and  eventually  produces  chlorosis.  This  is  to  be  expected 
since  magnesium  is  a  constituent  of  chlorophyll.  Cell  division  in  the 
epidermis  is  also  affected. 

A  lack  of  calcium  interferes  with  carbohydrate  transportation  and 
utilization,  but  does  not  stop  its  manufacture.  These  disturbances 
may  be  associated  with  the  formation  by  calcium  of  insoluble  salts  with 
substances  which  are  products  of  carbohydrate  utilization,  as  oxalic 
acid.  A  lack  of  calcium  would  result  in  an  accumulation  of  oxalic 
acid,  which  is  toxic  in  solution.  This  might  be  expected  to  interfere 
with  the  processes  of  carbohj^drate  utilization.  Root  growth  is  retarded 
or  stopped,  an  effect  already  mentioned  as  resulting  from  an  excess 
of  magnesium.  Hence  some  of  the  effects  of  calcium  deficiency  may 
be  associated  with  the  resultant  effect  on  the  calcium-magnesium  ratio. ^^^ 

Chlorine. — Though  chlorine  is  not  an  essential  element,  some  mention 
should  be  made  here  of  the  effects  of  an  absence  of  chlorine.  There 
are  conditions  in  the  field  under  which  the  best  development  occurs 
only  when  chlorides  are  added  to  the  soil.""  Recent  investigations  show 
that  the  effects  of  chlorides  are  markedly  different  on  different  plants, 
but  that  in  many  cases  they  serve  directly  or  indirectly  as  a  fertilizer. ^^^ 

AN  ANALYSIS  OF  THE  FERTILIZER  PROBLEM 

The  data  that  have  been  presented  on  the  factors  affecting  soil 
productivity  on  the  one  hand  and  the  metabolic  processes  going  on  within 
the  plant  on  the  other,  emphasize  the  incompleteness  of  the  knowledge 


200  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

of  plant  nutrition.  Much  important  information  has  been  obtained 
regarding  changes  occurring  in  the  soil  and  something  is  known  of  the 
synthesis,  translocation,  storage  and  utilization  of  organic  materials. 
At  best,  however,  this  information  is  fragmentary  and  much  generah- 
zation  regarding  the  use  of  fertilizers  in  the  orchard  is  unsafe.  Some 
idea  of  the  complexity  of  the  problem  is  obtained  when  we  consider 
the  numerous  ways  in  which  fertilizers  may  act:  (1)  to  change  conditions 
in  the  soil  and  (2)  to  disturb  or  restore  equilibria  within  the  plant. 
Among  the  more  important  of  these  methods  of  action  may  be  mentioned 
the  following: 

1.  Altering  the  physical  properties  of  the  soil. 

2.  Affecting  the  displacement  (lyotropic  succession)  of  various  elements. 

3.  Changing  the  solubility  of  other  soil  constituents. 

4.  Changing  the  availability  of  other  soil  constituents. 

5.  Changing  the  concentration  of  the  soil  solution. 

6.  Changing  the  reaction  of  the  soil  solution. 

7.  Influencing  bacterial  activity  in  the  soil. 

8.  Correcting  or  disturbing  the  balance  between  certain  soil  constituents,  e.g., 
calcium  and  magnesium  antagonism. 

9.  Stimulating  or  checking  chemical  reactions  in  the  soil  or  absorption  by  the 
roots. 

10.  Acting  as  toxins  or  protecting  against  their  influence. 

11.  Serving  directly  as  nutrients  for  the  plant. 

12.  Restoring  or  disturbing  chemical  equilibria  within  the  plant  after  absorption. 

The  Fertilizer  Requirements  of  the  Orchard. — In  the  discussion  that 
has  preceded  some  attention  has  been  devoted  to  each  of  these  factors 
in  the  nutrition  of  the  plant.  There  has  been  presented  also  a  general 
resume  of  some  of  the  available  information  regarding  synthesis,  trans- 
location and  use  of  certain  plant  constituents.  Incidentally  the  following 
facts  have  been  brought  out: 

1.  Many  elements  that  evidently  are  not  required  are  found  in  plants. 
Seldom  are  they  harmful;  they  are  merely  tolerated.  Among  them  may 
be  mentioned  sihcon,  aluminum,  sodium,  manganese,  titanium  and 
probably  chlorine.  These  elements  are  not  required  in  fertilizers.  They 
may  be  combined  with  certain  others  that  are  of  importance  and  they  may 
have  some  indirect  influence  upon  the  physical  condition  of  the  soil  or  the 
chemical  nature  of  the  soil  solution.  They  may  often  serve  a  useful  pur- 
pose in  furnishing  some  of  the  so-called  "indifferent"  ash  and  occasionally 
some  distinctly  beneficial  response  attributable  to  their  presence  may  be 
obtained  when  they  are  carried  in  fertihzers,  but  on  the  whole  they  need 
not  be  given  serious  consideration  in  the  problem  of  orchard  fertihzation. 

2.  Certain  elements  are  found  universally  in  plants  and  are  necessary 
constituents;  however,  except  in  very  unusual  cases,  they  exist  in  the  soil 
in  sufficient  quantities  and  in  forms  sufficiently  available  to  meet  the 
requirements  of  orchard  trees.     The  plant  often  takes  up  more  than  it 


SURPLUSES  AND  DEFICIENCIES  201 

uses.  This  surplus  is  merely  tolerated  and  usually  no  harmful  influence 
results.  Among  these  elements  may  be  mentioned  potassium,  calcium 
and  magnesium.  As  with  the  preceding  list,  their  application  in  fertilizers 
may  indirectly  benefit  the  plant  through  improving  physical  and  chemical 
conditions  within  the  soil,  or  restoring  a  proper  ratio  between  them  in  the 
case  of  the  last  two. 

It  would  seem  that  sufficient  evidence  to  support  these  statements  has  been 
presented  in  the  discussion  of  the  individual  elements  that  has  preceded.  It  is 
realized,  however,  that  they  run  counter  to  the  opinions  that  have  been  expressed 
in  a  great  number  of  published  statements  dealing  with  this  question,  to  many 
recommendations  that  have  been  made  for  the  fertilization  of  fruit  trees,  to 
what  has  in  some  instances  become  more  or  less  well  established  practice  and  to 
the  apparent  results  of  certain  plot  experiments.  This  is  true  particularly  in  the 
cases  of  potassium  and  calcium.  It  seems  desirable,  therefore,  to  bring  together 
the  results  of  some  of  the  orchard  fertilizer  experiments  with  potash  and  lime 
and  examine  them  somewhat  critically.  Table  66  presents  such  data  gathered 
from  many  sources.  It  does  not  include  all  the  records  that  might  be  assembled, 
but  it  represents  the  results  of  American  plot  trials. 

In  some  cases  the  application  of  potassium-  or  of  calcium-carrying  fertilizers 
has  resulted  in  increased  yields;  in  others  in  decreased  yields.  The  increases 
outweigh  the  decreases  in  both  number  and  amount;  but  in  the  Pennsylvania 
experiments  alone,  of  those  included  in  the  table,  are  the  increases  striking  or 
to  be  regarded  as  of  considerable  significance.  These  particular  Pennsylvania 
records  are  extremes  purposely  chosen  from  a  large  number,  the  great  majority 
of  which  show  no  such  marked  response  from  potash  applications.  Furthermore, 
the  different  check  plots  in  these  two  orchards  show  such  variation  as  to  justify 
some  hesitancy  in  drawing  conclusions  when  comparing  the  results  of  one  fer- 
tilizer treatment  with  those  of  another  on  a  plot  some  distance  removed  from 
the  first.  For  instance,  it  may  be  questioned  if  the  plots  treated  with  lime  alone 
and  with  nitrogen  alone  were  as  good  at  the  outset  as  those  receiving  nitrate  of 
soda  and  muriate  of  potash.  In  nearly  every  case  in  which  comparison  is  possible 
between  potash  or  lime  treated  plots  and  those  treated  with  nitrogen  alone  or  in 
combination,  nitrogen  stands  out  as  the  element  most  needed,  the  one  from  the 
application  of  which  the  greatest  response  is  obtained.  The  fact  that  in  most 
cases  the  application  of  nitrogen  alone  resulted  in  yields  exceeding  those  afforded 
by  potash  or  lime  is  further  evidence  that  there  was  an  ample  supply  of  these 
two  elements  in  the  soil  for  larger  crop  production,  that  they  were  present  in  an 
available  form  and  that  they  were  not  the  real  hmiting  factors.  Theoretically 
potassium  and  calcium  are  to  be  considered  as  possible  limiting  factors  just  as 
nitrogen  or  iron  or  phosphorus  or  sulfur.  Here  and  there  is  to  be  found  evidence 
that  occasionally  they  actually  are  not  present  in  an  available  form  and  in 
quantities  sufficient  for  the  trees'  requirements,  but  in  the  great  majority  of 
cases  there  is  no  occasion  to  supplement  the  supply  already  present  in  the  soil. 

3.  Certain  elements,  such  as  copper,  arsenic  and  lead,  are  occasionally 
found  in  plant  tissues  and  when  present  in  considerable  amounts  they 
have  toxic  effects.     However,  their  presence  is  the  result  of  spray  applica- 


202  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Table  66. — Influence  of  Potash-carrying  Fertilizers  upon  Fruit  Yields 


Investigator 


Alderman^.  .  .  . 
Alderman-.  .  .  . 
Alderman^.  .  .  . 

Mc  Cue"i 

Mc  Cue"i 

Mc  Cue"i 

Gladwin'* 

Gladwin'* 

Gladwin'* 

Gladwin'* 

Bailout 

Ballous 

Hedrick,  et  alw 
Hedrick,  et  al^' 

Reimer'5* 

Reimeri" 

Reimeris* 

Reimeris* 

CoUison'o 

CoUison'" 

ColUson'" 

Collison^o 

CoUison^o 

CoUison^o 

Chandler25.  ..  . 

Brown^o 

Franklin  6  8 

Munsoni37.  .  . 
Munsoni37.  .  .  . 

Stewarti's 

Stewart'" 

Stewart! '8 

Stewarti'8 

Stewart"' 

Stewart!" 

Stewarti" 

Stewart'" 


State 


West  Virginia 
West  Virginia 
West  Virginia 
Delaware 
Delaware 
Delaware 
New  York 

New  York 
New  York 

New  York 

Ohio 

Ohio 

New  York 

New  York 

Oregon 

Oregon 

Oregon 

Oregon 

New  York 

New  York 

New  York 

New  York 

New  York 

New  York 

Missouri 

Oregon 

Massachusetts 

Maine 

Maine 

Pennsylvania 

Pennsylvania 

Pennsylvania 

Pennsylvania 

Pennsylvania 

Pennsylvania 

Pennsylvania 

Pennsylvania 


Crop 

Fertilizer 

Yield 

Yield  of 
check 

Gain,  per 
cent. 

Peach 

K  +  P 

42.42 

49.48 

-14.2 

Peach 

K  +  N 

71.93 

49.48 

45.3 

Peach 

Lime 

60.82 

49.48 

22.9 

Peach 

K 

764.40 

684.30 

11.7 

Peach 

K 

1565.90 

684.30 

129.6 

Peach 

N 

2210.80 

684.30 

223.0 

Grape 

K2SO4 

NaN03  + 

940. 50 

711.00 

32.3 

Grape 

K2SO4 

1185.50 

711.00 

66.7 

Grape 

N+K  +  P 
N+K+P+ 

1230. 50 

711.00 

73.0 

Grape 

Lime 

1118.00 

711.00 

57.2 

Apple 

KCl 

96.00 

69.90 

27.2 

Apple 

NaNOs 

315.60 

69.90 

351.2 

Apple 

KCl 

4877. 00 

4375.00 

11.5 

Apple 

KCl  +  P  +  N 

4823. 50 

4375.00 

10.2 

Apple 

KCl 

3.31 

2.85 

16.1 

Apple 

N 

14.50 

2.85 

408.5 

Peach 

KCl 

30.00 

30.80 

-2.6 

Peach 

N 

42.25 

30.80 

37.2 

Apple 

N+P  +  KCl 

79.00 

76.80 

2.9 

Apple 

N  +  P 

77.10 

76.80 

0.4 

Cherry 

N  +  P  +  KCl 

122.70 

111.60 

9.9 

Cherry 

N  +  P 

105. 90 

111.60 

-4.9 

Grape 

Lime 

280. 00 

220.  00 

27.2 

Grape 

Lime 

261.00 

443.00 

-69.7 

Strawberries 

KCl 

11.10 

14.20 

-21.8 

Strawberries 

K2SO4 

222.00 

230.  00 

-3.5 

Cranberries 

K 

43.25 

48.18 

-10.3 

Apples 

KCl 

f.60 

2.30 

11.5 

Apples 

K2SO4 

2.28 

2.30 

-0.9 

Apples 

N  +  KCl 

318.20 

117.80 

170.2 

Apples 

N 

186.20 

98.00 

90.0 

Apples 

P  +  KCl 

113.10 

75.60 

49.6 

Apples 

P  +  K2SO4 

91.30 

93.20 

-2.4 

Apples 

Lime 

73.70 

67.70 

8.9 

Apples 

N  +  KCl 

350.  40 

230. 30 

52.1 

Apples 

N 

236.  80 

208. 40 

13.1 

Apples 

Lime 

61.00 

53.80 

13.4 

tions  or  unusual  conditions  of  one  kind  or  another  and  the  problems 
incident  to  their  presence  are  hardly  to  be  considered  as  belonging  in  the 
field  of  nutrition. 

4.  Two  elements,  phosphorus  and  sulfur,  are  found  in  all  soils  and 
in  all  plants.  Though  they  are  necessary  for  plant  growth,  deciduous 
fruits  are  able  ordinarily  to  obtain  all  of  them  they  require.  However, 
their  apphcation  in  fertiUzers  is  frequently  warranted,  mainly  because 
of  their  indirect  value  to  the  trees  through  the  effect  they  may  have 
on  intercrops  or  cover  crops.  Some  attention  is  devoted  to  this  phase 
of  the  orchard  fertihzer  problem. 

5.  Two  other  essential  elements,  iron  and  nitrogen,  though  found  in  all 
soils,  are  often  either  deficient  in  quantity  or  present  in  forms  unavailable 


SURPLUSES  AND  DEFICIENCIES  203 

to  the  plant.  The  result  is  arrested  development  or,  in  extreme  cases, 
the  appearance  of  pathological  conditions.  An  excess  of  nitrogen 
also  leads  to  disturbed  nutritive  relations  and  to  pathological  symptoms. 
Considerable  attention  has  already  been  devoted  to  the  question  of  iron 
deficiencies  and  to  methods  of  dealing  with  them. 

6.  Elaborated  organic  compounds  of  many  kinds  have  uses  in  growth 
processes  equal  in  importance  to  those  of  the  mineral  constituents. 
Though  for  the  most  part  they  are  synthesized  within  the  plant,  the 
materials  for  their  manufacture  are  water,  carbon  dioxide  and  the 
nutrients  just  mentioned. 

It  is  therefore  evident  that  the  question  of  fertilizers  for  deciduous 
fruits,  in  so  far  as  such  fertilizers  serve  more  or  less  directly  as  nutrients 
for  the  plant,  centers  largely  around  the  proper  use  of  nitrogen.  This  is 
far  from  stating  that  fertilizers  other  than  those  carrying  nitrogen  are 
never  of  direct  nutrient  value.  For  instance,  work  with  grapes  and 
strawberries^^  suggests  strongly  that  sulfur-carrying  fertilizers  in  the  one 
case  and  phosphorus-carrying  compounds  in  the  other  supplied  the  plants 
directly  with  these  nutrients,  though  it  is  possible  that  certain  of  their 
indirect  influences  may  have  been  more  important  than  their  direct 
effects.  Furthermore,  there  is  reason  to  believe  that  many  of  the  results 
obtained  from  the  use  of  phosphorus-,  potassium-  and  calcium-carrying 
fertilizers  on  deciduous  fruits  of  different  kinds  and  generally  attributed 
to  their  direct  nutrient  value  have  in  reality  been  due  to  their  functioning 
in  other  ways.  These  statements  are  not  made  to  minimize  the  possible 
effects  or  uses  of  fertilizing  elements  other  than  nitrogen.  That  they 
often  are  of  value  in  the  orchard  there  is  no  doubt.  The  point  is  that 
nitrogenous  fertilizers  act  more  or  less  directly  as  nutrient-carrying 
substances;  others  act  rather  indirectly  through  correction  of  unfavorable 
soil  conditions  or  by  protecting  the  orchard  plants  from  harmful  sub- 
stances or  only  indirectly  as  nutrients  through  assisting  the  growth  of 
intercrops  or  cover  crops.  Clear  differentiation  between  these  different 
modes  of  operation  is  important,  for  only  when  there  is  a  clear  conception 
of  how  a  fertilizer  works  can  it  be  used  intelligently  and  with  certainty 
as  to  results. 


CHAPTER  XII 
THE    APPLICATION    OF    NITROGEN -CARRYING    FERTILIZERS 


The  general  purpose  of  fertilizer  application  is  to  increase  yields. 
In  the  orchard  this  may  result  from  larger  tree  growth,  from  increased 
fruit  bud  formation,  from  better  setting  of  the  fruit,  from  the  production 
of  fruit  of  larger  size,  or  from  a  combination  of  two  or  more  of  these 
rather  distinct  responses. 

The  Influence  of  Nitrogenous  Fertilizers  on  Vegetative  Growth. — 
An  abundant  supply  of  available  nitrogen  in  the  soil  has  long  been 
associated,  by  well  informed  gardeners,  with  strong,  vigorous  growth. 
So  well  is  this  connection  recognized  that  gardeners  and  florists  generally 
have  become  skilled  in  the  art  of  using  nitrogenous  fertilizers  for  vege- 
tables and  ornamental  plants.  Fruit  growers,  however,  though  inclined 
to  recognize  the  general  value  of  such  fertilizers,  have,  for  one  reason  or 
another,  not  employed  them  to  any  considerable  extent  and  it  is  not  until 
recent  years  that  much  experimental  evidence  has  been  available  as  to 
their  place  in  orchard  practice. 

In  Peaches. — Alderman^  reported  the  results  of  a  series  of  fertilizer 
experiments  with  peaches  in  West  Virginia.  The  trees  were  growing  in 
a  rather  thin  shale  loam,  a  soil  commonly  used  in  that  section  for  apples 
and  peaches,  though  it  would  generally  be  classed  as  rather  unproductive. 
Some  of  his  data  pertaining  to  shoot  and  leaf  growth  are  assembled  in 
Table  67.     They  show  that  wherever  nitrogen  was  used,  shoot  growth  was 

Table  67. — Effect  of  Fertilization  on  Vegetative  Growth  of  the  Peach 
{After  Alderman-) 


Fertilizer  treatment 


Average 
shoot 

length, 
4-year 

average 

(inches) 


Average 
leaf  area, 
3-year 
average 
(square 
inches) 


Number 


per  tree, 
3-year 
average 


Leaf  area    „ 

Per  cent 


per  tree, 

3-year 

average 

(square 

feet) 


of  fruit 
buds, 
4-year 

average 


Nitrogen  and  phosphoric  acid. 

Nitrogen  and  potash 

Complete  fertilizer 

Potash  and  phosphoric  acid. . 

Check 

Complete  fertilizer 

Complete  with  potash  doubled 
Complete  with  potash  tripled.  . 
Lime. 


16 

10 

14 

47 

15 

00 

8 

16 

7 

28 

14 

40 

15 

59 

15 

00 

7 

84 

28 
26 
06 
63 
89 
12 
39 
4.26 
3.26 


25,424 
24,808 
23,208 
8,768 
10,596 
29,536 
32,368 
22,648 
14,172 


755.6 
734.4 
654.3 
160.1 
212.6 
845.0 
986.7 
670.0 
320.8 


80.6 
75.5 
74.0 
58.0 
57.9 
76.6 
75.2 
76.2 
64.4 


204 


THE  APPLICATION  OF  NITROGEN -CARRYING  FERTILIZERS    205 

practically  doubled;  this  increased  shoot  growth  was  accompanied  by  a 
corresponding  increase  in  leaf  number.  Furthermore  there  was  a  great 
gain  in  leaf  size;  this  increase  coupled  with  the  greater  number  of  leaves 
multiplied  the  total  leaf  area  by  three  or  four.  In  commenting  on  this 
effect  of  nitrogen,  Alderman-  remarks:  "...  for  every  foot  of  bearing 
surface  on  the  check  tree  the  fertilized  tree  carried  over  23^-^  feet  of  wood 
upon  which  fruit  might  be  borne.  This  difference  in  size  has  been  increas- 
ing so  that  the  ratio  would  be  much  greater  in  favor  of  the  nitrogen 
fertilized  trees  at  the  present  time  after  4  years  of  treatment."  Inci- 
dentally the  data  presented  in  this  table  verify  earlier  statements  to  the 
effect  tjiat  few  orchards  require  potash,  phosphoric  acid  or  lime. 

In  Apples. — Lewis  and  Allen^^^  have  reported  practically  the  same 
influence  on  the  shoot  growth  and  foliage  of  apple  trees  in  the  Hood  River 
valley,  Ore.,  when  nitrate  of  soda  was  applied  to  bearing  apple  trees  in  a 
rather  weakened  condition.  They  observed  an  even  more  striking  change 
in  the  color  of  the  foliage,  which  was  pale  j^ellowish  green  in  the  check 
plots  and  dark  rich  green  in  those  that  were  fertilized.  Still  another 
effect  noted  many  times  is  delayed  leaf  fall.  This  delay  may  vary  from 
a  few  days  to  several  weeks.  Since  the  leaves  late  in  the  season  can 
build  elaborated  foods  for  winter  storage  and  spring  utilization,  this 
delayed  maturity  may  bring  about  an  accumulation  of  materials  which 
might  promote  greater  vegetative  growth  the  following  season  and  main- 
tain the  tree  in  a  more  vigorous  condition.  At  the  same  time,  however, 
danger  from  sharp  fall  frosts  or  early  freezes  is  increased,  especially  if 
applications  are  heavy  enough  to  force  the  formation  of  new  vegetative 
tissues  late  in  the  season.  Consequently  considerable  caution  should  be 
exercised  to  apply  nitrogen  so  as  to  postpone  leaf  fall  but  not  materially 
to  delay  maturity  of  wood. 

In  Strawberries. — Chandler-^  reports  that  nitrogen  in  either  nitrate 
of  soda  or  dried  blood  applied  to  strawberry  plants  in  the  spring  before 
the  crop  is  harvested  causes  excessive  leaf  growth  and  that  when  the 
latter  material  is  applied  even  a  year  before  the  crop  is  to  be  harvested 
it  causes  considerably  increased  vegetative  growth.  This  excessive 
leaf  growth  was  found  to  be  associated  with  decreased  fruit  production. 
I  Negative  Results.  Nitrogen  Not  a  Limiting  Factor. — On  the  other 
Tiand,  Hedrick  and  Anthony^*^  in  reporting  the  results  of  20  years  of 
experimentation  with  fertilizers  in  apple  orchards  in  New  York  state: 
"...  heavy  applications  of  nitrogen  in  a  complete  fertilizer  and  in  ma- 
nure have  not  increased  tree  growth. "  The  results  obtained  by  Stewart^^^ 
in  Pennsylvania  from  the  use  of  nitrogen-carrying  fertilizers  in  bearing 
apple  orchards  are  for  the  most  part  in  accord  with  those  of  Lewis  and 
Allen;  at  least  most  of  his  applications  of  nitrogenous  fertilizers  resulted 
in  increased  vegetative  growth.  However,  some  of  these  increases 
were  comparatively  small  and  there  were  a  few  instances  in  which  no 


206 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


increase  was  obtained.  Gourley^^  found  substantially  the  same  general 
condition  in  his  experimental  plots  in  New  Hampshire — particularly 
during  the  early  years  of  the  experimental  treatments.  Table  68 
assembled  from  data  presented  by  him  and  some  of  his  associates,^ 
recapitulating  the  first  5-years'  results,  explains  some  of  the  preceding 
statements  that  at  first  appear  more  or  less  conflicting.  This  table 
shows  practically  no  increased  vegetative  growth  accompanying  the 
use  of  fertilizers,  as  compared  with  plots  under  clean  cultivation  or  plots 
growing  annual  cover  crops,  even  though  one  of  the  fertilizers  contained 


Table  68. 


-Response   in   Vegetative   Growth  from   Fertilizer  Applications 

{After  Gourleif^) 


Treatment 

Nitrates 
in  soil  in 
parts  per 

million, 
4-year 

average 

Yield  of 
fruit,   5- 

year 
average 

Shoot 
growth, 

4-year 
average 

Size    of 
fruit,  4- 

year 
average 

Leaf 
area, 
1913 

Fresh 

leaf 

weight, 

1913 

Sod        

3.18 

17.40 
33.91 

100 
132 
176 
213 
216 

191 

195 

166 
163 
161 

100 
140 
163 
190 
212 

222 

198 

200 
217 
202 

100 
168 
165 
142 
135 

165 

155 

168 
196 
206 

100 
107 
113 
119 

124 

129 

126 

126 
125 
131 

100 

111 

Cultivation  every  even  year 

117 
123 

123 

Cultivation,  cover  crop  and  complete 

135 

Cultivation,  cover  crop  and  complete 

131 

Cultivation,   cover  crop  and  excess 
PjOs                                

131 

Cultivation,  cover  crop  and  excess  N. 

Cultivation,   cover   crop  and   excess 

K-0          

128 
134 

relatively  large  amounts  of  nitrogen.  However,  soil  cultivation, 
particularly  when  coupled  with  cover  crops,  made  available  to  the 
plants  an  abundant  supply  of  nitrogen — a  supply  that  obviously  was 
present  in  the  sod  land,  but  unavailable.  This  abundant  supply  met 
the  trees'  nutritive  requirements  and  the  surplus  resulting  from  appli- 
cations of  nitrate  did  not  effect  any  consistently  increased  growth. 
In  a  report  on  the  same  series  of  experiments  5  years  later  Gourley^" 
states  that  though  there  was  no  special  or  marked  increase  in  yield  in 
the  fertihzed  plots  over  those  not  receiving  fertihzer  "the  orchard  is 
developing  in  that  direction."  In  other  words,  the  period  of  maximum 
production  without  applications  of  nitrogenous  fertilizers  had  been 
reached.  This  period  might  last  for  a  number  of  years,  or  be  of  short 
duration;  in  either  case  greater  and  greater  increases  in  vegetative 
growth  and  fruit  production  could  be  expected  from  proper  fertiliza- 
tion.    As  trees  increase  in  age  and  size  they  require  larger  amounts  of 


THE  APPLICATION  OF  NITROGEN-CARRYING  FERTILIZERS    207 

nutrients  and  with  the  actual  reduction  in  the  total  nitrogen  supply  of 
cultivated  soils  taking  place  each  year  it  is  easy  to  see  how  the  margin  of 
safety  may  disappear  entirely.  Increased  vegetative  growth  follows 
the  apphcation  of  nitrogen-carrying  fertilizers  only  when  the  supply 
of  available  nitrates  in  the  soil  is  less  than  the  plant  must  have  for  its 
best  growth  and  there  is  a  limit  to  what  the  plant  can  use.  Within 
limits,  surplus  amounts  of  available  nitrogen,  like  surplus  amounts  of 
available  potassium  or  calcium  or  other  materials,  are  simply  tolerated. 
Analyses  are  not  at  hand  showing  the  exact  amounts  of  available  nitrates 
in  the  West  Virginia  and  Oregon  soils  to  which  reference  has  just  been 
made,  but  it  may  be  presumed  that  they  contained  very  small  amounts 
or  amounts  smaller  than  those  required  by  the  trees  for  maximum 
growth  and  production. 

Many  orchards  will  not  respond  to  nitrogenous  fertilizers  because 
the  soils  and  the  methods  of  soil  management  are  of  such  a  character 
that  nitrogen  is  not  a  limiting  factor.  On  the  other  hand  experience 
shows  that  there  are  many  orchards  in  which  nitrogen  is  a  limiting  factor 
and  in  which,  consequently,  nitrogen-carrying  fertilizers  can  be  used 
profitably.  To  conclude  from  one  experiment  or  a  series  of  experiments 
giving  negative  results  that  orchard  fertilization  in  general  is  not  needed 
or  that  it  does  not  pay  is  as  erroneous  as  it  is  to  conclude  from  striking 
returns  on  a  nitrate  deficient  soil  that  orchards  generally  should  be 
regularly  fertilized  with  that  element.  Statements  that  have  been  made 
give  some  idea  of  the  symptoms  of  nitrogen  starvation.  Short,  slender 
shoot  growth  and  small  pale  leaves  are  perhaps  the  most  frequent  indices 
of  this  condition,  though  there  are  many  others.  However,  some  of 
these  symptoms  likewise  characterize  injuries  resulting  from  deficient 
water  supply,  borer  attack  or  other  troubles  and  care  should  be  exercised 
to  identify  the  real  cause  or  causes  of  the  trouble  before  deciding  upon 
fertilization  of  any  considerable  area. 

A  given  supply  of  available  nitrogen  in  the  soil  though  entirely  ade- 
quate for  the  requirements  of  one  fruit  crop  may  not  prove  sufficient  for 
the  best  growth  of  another.  Thus  Chandler-'^  has  found  that  in  a  certain 
clay  loam  in  New  York  applications  of  nitrogen-carrying  fertilizers 
resulted  in  greatly  increased  shoot  and  leaf  growth  in  gooseberries  and 
red  raspberries,  though  currants  and  black  raspberries  showed  but  little 
response.  Reimer^^^  reports  that  in  the  Rogue  River  of  southern  Oregon 
the  Yellow  Newton  apple  does  not  respond  to  fertihzer  applications  so 
readily  as  Esopus  (Spitzenburg).  Much  yet  remains  to  be  done  toward 
determining  the  actual  total  yearly  nitrate  requirements  of  different 
fruit  crops  and  also  their  varying  requirements  from  season  to  season 
with  increasing  age. 

Influence  of  Nitrogen  On  Blossom  Bud  Formation. — It  is  not  the 
intention  at  this  point  to  discuss  in  detail  the  many  factors  influencing 


208  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

blossom  bud  formation.  It  is  generally  conceded,  however,  that  fruit 
bud  initiation  is  in  a  way  a  response  to  nutritive  conditions  within  the 
plant  and  it  has  been  shown  that  these  nutritive  conditions  are  modified 
by  the  nature  of  the  soil  solution.  At  least  theoretically,  then,  it  should 
be  possible  to  influence  fruit  bud  formation  through  the  use  of  fertilizers. 

In  Peaches. — In  a  preceding  paragraph  Alderman-  is  quoted  as  report- 
ing that  in  his  fertilizer  experiments  with  peaches  in  West  Virginia  the 
application  of  nitrogen-carrying  fertilizers  resulted  in  more  than  double 
the  shoot  growth  and  hence  double  the  amount  of  possible  fruit-bearing 
surface.  Data  on  fruit  bud  formation  on  these  shoots  are  presented  in 
the  last  column  of  Table  67.  If  these  figures  for  numbers  of  fruit  buds 
per  unit  of  shoot  length  were  plotted,  the  curve  would  take  the  same  general 
direction  as  one  for  figures  on  total  shoot  length,  though  the  two  would 
not  be  exactly  parallel.  In  commenting  on  these  data  Alderman^  says: 
the  ' '  table .  .  .shows  during  the  first  3  years  a  uniformly  high  percentage 
of  fruit  buds  formed  on  the  nitrogen-fed  plots  and  a  correspondingly  low 
percentage  in  plots  4,  5  and  9  (those  receiving  nothing,  potash  and 
phosphoric  acid  or  lime  only).  By  100  per  cent,  set  of  buds  we  mean  that 
practically  all  the  new  growth  is  filled  with  double  buds  from  base  to  tip 
.  .  .  while  a  50  per  cent,  set  would  indicate  that  buds  were  found  over 
only  about  one-half  the  twig  and  were  single  in  many  cases." 

In  Apples. — The  situation  is  somewhat  more  complicated  in  fruits 
like  the  apple  that  bear  mainly  upon  spurs.  However,  Roberts^^^  has 
reported  that  there  is  a  distinct  correlation  between  the  annual  increase 
in  length  of  spurs  and  their  blossom  bud  formation.  Both  those  spurs 
making  a  very  short  and  those  making  a  very  long  annual  growth  did 
not  form  many  fruit  buds,  but,  on  the  other  hand,  those  that  made  a 
medium  growth  were  highly  fruitful.  Length  was  in  turn  correlated 
directly  with  number  of  leaves  and  total  leaf  area  and  within  certain 
hmits  {i.e.,  for  the  shorter  spurs)  there  was  also  a  correlation  between 
spur  length  and  average  leaf  area.  Experiments  on  the  influence  of  nitrog- 
enous fertilizers  on  spur  length  are  reported  by  Roberts^''^  as  follows:  "In 
1918  the  difference  in  spur  growth  of  non-bearing  Wealthy  was  as  follows: 
check  trees  4.89  mm.;  nitrate  of  soda  11.98.  In  1919,  when  there 
was  a  larger  growth  on  checks  than  usual,  less  difference  was  also  noted. 
The  figures  for  different  trees  than  those  used  in  1918  are:  check  7.41; 
nitrate  9.25."  In  general  the  influence  of  the  nitrate  was  to  increase 
the  length  of  the  spurs  and  consequently  leaf  numbers  and  total  leaf 
areas.  In  the  trees  with  spurs  too  short  for  fruit  bud  formation  the  effect 
would  be  to  encourage  that  process;  in  those  trees  with  spurs  averaging 
just  long  enough  or  a  little  too  long  for  maximum  fruit  formation  the  effect 
would  be  to  discourage  it.  Roberts'^^  also  points  out  certain  correlations 
between  the  amount  of  shoot  growth  and  the  number  and  character  of 
fruit  spurs.     This  suggests  a  further  indirect  correlation  between  fertilizer 


THE  APPLICATION  OF  NITROGEN-CARRYING  FERTILIZERS    209 


applications  and  fruit  bud  formation,  for  the  amount  of  shoot  growth  is 
greatly  influenced  by  the  available  nitrate  supply.  The  work  of  Hookeri"*' 
and  others  showing  the  importance  of  the  synthesis  and  storage  of  organic 
compounds  in  late  summer  and  fall  in  determining  the  amount  and  char- 
acter of  growth  early  the  next  season  suggests  still  further  indirect  correla- 
tions— correlations  no  less  important,  though  less  easily  recognized,  than 
those  first  mentioned. 

Influence  of  Nitrogen  on  the  Setting  of  Fruit. — The  influence  of 
nitrogenous  fertilizers  on  shoot  and  leaf  growth  and  on  the  formation 
of  fruit  buds  is  not  less  striking  than  their  effect  on  the  setting  of  fruit, 
especially  in  rather  weak  trees  that  still  bloom  heavily.  This  is  well 
brought  out  by  the  data  presented  in  Table  69,  for  apple  trees  in  the  Hood 
River  valley. 

Table  69.— Influence  of  Nitrate  of  Soda  Applications  upon  Set  of  Fruit  in 
'_/  Two  Hood  River  (Oregon)  Apple  Orchards 

{After  Lewis  and  Allen^-^) 


Number  of 

Percentage 

Percentage 

Average 

Treatment 

blossoming 

of  fruit  set 

of  fruit  set 

yield  per  tree 

spurs 

June  4 

Sept.  30 

(bushels) 

First  orchard: 

Check  (unfertilized) 

483 

35.3 

16.4 

3.75 

Fertilized  with  nitrate.  .  . 

.542 

68.0 

.30.7 

21.50 

Second  orchard: 

Check  (unfertilized) 

386 

9.0 

4.6 

1.33 

Fertilized  with  nitrate .  .  . 

620 

58.0 

15.1 

9.50 

^The  setting  of  fruit  in  the  fertilized  plots  ranged  from  100  to  300  per 
cent,  higher  than  that  in  the  check  plots.  Furthermore  this  influence 
was  evident  right  after  blossoming,  certainly  not  later  than  the  time  of 
the  so-called  June  drop.  This  was  only  a  very  short  time  after  applica- 
tion and  shaws  the  prompt  response  obtained  from  such  a  quickly  avail- 
able fertilizer.  Similar  results  have  attended  the  spring  use  of  nitrate 
of  soda  in  many  other  experiments  with  apples  and  pears.  Indeed  so  well 
is  the  use  of  this  fertilizer  gaining  recognition  for  this  purpose  that  large 
quantities  are  now  used  in  commercial  orchards  to  deal  with  many  of  the 
difficulties  that  formerly  were  considered  pollination  problems.  There 
are  few  data  showing  the  influence  of  quickly  available  nitrogenous 
fertilizers  on  the  set  of  other  deciduous  fruits,  such  as  peaches,  cherries, 
apricots  and  grapes.  In  view  of  their  known  influence  in  apples  and 
pears  this  subject  demands  careful  investigation. 

Influence  of  Nitrogen  on  Size  of  Fruit. — Since  the  size  the  fruit 
attains  is  an  expression  of  the  plant's  vegetative  activities  it  may  be 
supposed  that  the  factors  or  treatments  leading  to  an  increased  shoot 


210 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


and  leaf  development  will  likewise  lead  to  increased  size  of  fruit.  This 
expectation  is  justified  by  the  results  of  many  field  trials  with  orchard 
fertilizers.  Representative  of  many  data  that  might  be  introduced 
are  those  presented  in  Table  70  for  apples.  In  terms  of  percentages, 
the  increase  in  size  there  reported  amounts  to  25  or  over. 


Table  70. 


-Size  of  Apples  as  Influenced  by  Nitrate  Applications 

(After  Lewis  and  Allen^-^) 


Per  cent,  grading 

Treatment 

175  to  150  per 
bushel 

138  to  112  per 
bushel 

100  per  bushel 
and  larger 

Check  (no  fertilizer) 

22.09              39.76 
2  28              26  91 

38.15 
70  76 

Pears  from  nitrate  fertilized  trees  in  the  Rogue  River  valley  have 
been  reported  to  average  about  178  to  the  box,  while  those  from  unfertil- 


/ 

/ 

/ 

/ 

/ 

y 

/ 

y 

,\ 

)/ 

7 

n^:^ 

y' 

"v 

^ 

.^ 

/ 

^^% 

f 

___- 

y 

.V 

<^ 

\^^ 

y/ 

^^^ 

i^/7-d 

^/:f. 

"L- 



.-'- 

J, 

^-^"; 

/_ 

— 

<^< 

>/v 

^>x^. 

H 

s 

^\ 

^-- 

-^ 

^^ 

Fig.  25. — Response  of  apple  trees  to  fertilizer  treatments,  showing  increases  or  decreases 
in  yield,  fruit  setting  and  fruit  coloration  accompanying  increased  shoot  growth.  (Plotted 
from  data  given  by  Stewart. ^''^) 

ized  plots  averaged  225.^^"*     The  graphs  in  Figs.  25  and  26  indicate  in  a 
general  way  the  observations  of  Stewart  in  Pennsylvania  and  Alderman  in 


THE  APPLICATION  OF  NITROGEN-CARRYING  FERTILIZERS    211 


Virginia  on  the  influence  of  fertilizer  treatments  on  fruit  size,  especially 
as  increases  in  size  are  correlated  with  increased  or  decreased  vegetative 
growth  and  with  increased  or  decreased  yield.  In  some  of  the  cases 
reported  by  Stewart,  but  not  shown  in  the  graphs,  fertilizer  applications 
were  accompanied  by  decreased  size  of  fruit.     In  commenting  on  his 


120 


90 


80 


60 


50 


.-^0 


20 


^/^ata  Stewart^^*  says:  "In  the 
matter  of  fruit  size,  some  benefits 
are  indicated  .  .  .  but  they  have 
proved  less  as  a  rule  than  is  com- 
monly supposed.  Manure  has 
naturally  been  most  consistent  in 
increasing  the  average  size  of  the 
fruit,  probably  chiefly  on  account 
of  its  mulching  effect  .  .  .in 
general  we  believe  that  the  plant 
food  influence  will  always  be  sec- 
ondary to  moisture  conservation 
and  proper  thinning,  wherever 
greater  fruit  size  is  desired." 
Alderman^  in  his  fertilizer  work 
with  peaches  found  but  little  in- 
crease in  size  from  the  use  of 
fertilizers,  nitrogen  in  combination 
with  potash  showing  slight  gains.  0 
At  the  Missouri  Station  it  was 
found  that  in  some  cases  the  fer- 
tilization of  peaches  with  nitrogen  "i-O 
was  attended  by  a  marked  decrease         Fig.   26.— Response  of  peach  trees  to 

„   „      •-     ,1  •       1  fertilizer    treatments,    showing    increases   or 

m   Size  Ot   truit,  this  decrease  some-  decreases  in  yield   and  fruit  setting  accom- 

times  amounting  to  as  much  as  40  panying   increased   shoot   growth.      (Plotted 

,   „„„  from  data  given  by  Stewart.''*) 

per  cent. 202 

The  explanation  of  the  frequent  failure  of  the  fruit  from  fertilized 
trees  to  show  an  increase  in  size  over  that  from  unfertilized  trees  and  of 
the  occasional  decreases  in  size  lies  in  the  increased  wood  growth  and 
leaf  area  of  the  plants  and  consequently  in  their  increased  demand  for 
water.  As  this  increase  in  leaf  surface  may  sometimes  amount  to  over 
100  per  cent,  it  is  easy  to  understand  how  water  may  become  a  limiting 
factor.  Especially  is  this  true  when  it  is  remembered  that  the  osmotic 
concentration  of  the  leaves  is  greater  than  that  of  the  developing  or 
maturing  fruits  and  hence  in  times  of  stress  the  fruits  may  actually  lose 
water  to  the  leaves  which  supplies  their  transpiration  requirements 
and  keeps  them  turgid. ^^  This,  however,  is  an  indirect  effect  of  nitrog- 
enous fertilizers  on  size  of  fruit,  occasionally  important  in  orchard 
practice  and  suggesting  that  increased  attention  should  be  given  to 


r^ 

GROwnL^ 

f 

1 

>s.^ 

\ 

^ 
^ 

\ 

■A- 

— 

.-\ 

s,el2^ 

%r 

A] 

\, 

i  ^ 

/ 

1 

\ 

i 

/ 

i 

Si 

\ 

1 

\, 

'^ 

V\ 

"\ 

212  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

meeting  the  trees'  requirements  for  moisture  when  nitrogenous  fertilizers 
are  used.  It  also  raises  a  series  of  interesting  and  important,  but  wholly 
unanswered,  questions  as  to  the  relative  influence  different  fertilizers  may 
have  on  different  parts  of  the  tree — for  example,  roots,  leaves,  fruit.  It 
is  clear  that,  at  present,  there  are  no  means  of  increasing  the  size  of  fruit 
directly  through  the  use  of  any  particular  fertilizer.  Fertilizers  can  lead 
to  the  production  of  larger  fruit  only  as  they  lead  to  increased  vegetative 
growth  and  the  consequently  increased  amounts  of  manufactured  foods 
and  as  they  lead  to  a  greater  extension  of  the  root  system  and  to  a  conse- 
quently greater  intake  of  water  or  in  still  other  indirect  ways. 

Influence  of  Nitrogen  on  Color  of  Fruit. — There  has  been  much  dis- 
cussion in  pomological  Hterature  concerning  the  use  of  fertilizers  for 
aiding  the  coloration  of  fruits  and  applications  of  potash  and  phosphoric 
acid  have  been  rather  generally  recommended  for  this  purpose.  Hedrick 
was  one  of  the  first  to  submit  experimental  data  bearing  on  this  question. 
After  a  10-year  trial  with  several  varieties  in  an  old  New  York  apple 
orchard  growing  in  a  rather  heavy  clay  he  concluded  that  no  influence 
on  color  of  fruit  could  be  ascribed  to  the  potash  or  phosphoric  acid 
\/^  which  had  been  used.^"  Stewart ^''^  in  summarizing  the  results  of  his  k 
work  with  apples  in  Pennsylvania  says:  "None  of  the  fertilizer  treat- 
ments has  resulted  in  any  marked  improvement  in  color.  Slight 
and  irregular  benefits  are  shown  by  potash  and  by  some  of  the  phosphate 
applications,  but  nothing  of  any  importance  ..."  Some  of  the  graphs 
in  Figs.  25  and  26,  plotted  from  data  presented  by  Stewart,  furnish  clear 
evidence  in  support  of  his  conclusions.  Alderman^  reports  a  reduction  of  i^ 
the  red  color  in  peaches  accompanying  the  use  of  nitrogenous  fertilizers 
and  ascribes  it  to  late  maturity  and  to  increased  density  of  the  foliage. 
Conversely,  some  slight  increases  in  color  from  the  use  of  potash  or  phos- 
phoric acid  he  ascribes  to  the  slight  checking  effect  these  materials  some- 
times have  on  vegetative  growth.  It  is  significant  that  the  curves 
representing  average  influence  of  fertilizers  on  color  are  almost  exactly 
the  reverse  of  those  representing  their  influence  on  vegetative  growth.  . 
In  other  words,  the  two  phenomena,  those  of  color  formation  and  new 
vegetative  growth,  are  negatively  correlated. 

Influence  of  Nitrogen  on  Yield. — In  general  the  tendency  of  nitrog- 
enous fertilizers  is  to  increase  vegetative  growth,  promote  the  formation 
of  fruit  buds,  increase  the  percentage  of  flowers  setting  fruit  and  lead 
to  larger  size  in  the  individual  fruits.  It  is  inevitable  therefore  that  their 
general  influence  must  be  greatly  to  increase  yields.  Many  data  might 
be  presented  in  support  of  this  general  conclusion.  Those  given  in 
Tables  71  and  72  represent  some  of  the  more  striking  results  that  have 
been  obtained;  these,  however,  have  been  duplicated  in  orchards  in 
many  parts  of  the  country.  Table  73  is  particularly  interesting  as 
emphasizing  the  importance  of  nitrogen  compared  with  the  other  nutrient 


THE  APPLICATION  OF  NITROGEN-CARRYING  FERTILIZERS    213 


elements,  in  increasing  yields.  Perhaps  it  should  be  noted  that  the  trees 
in  both  of  these  orchards  were  in  a  rather  weak  vegetative  condition 
before  fertilizers  were  applied. 

Table  71.:^Influence    of   Quickly    Available   Nitrogenous    Fertilizers   on 
Yield  of  Apples  in  the  Hood  River  Valley 
{After  Lewis  and  Allen^-^) 
Treatment  Average    Yield    per    Tree 

(in  Loose  Boxes) 
0.90 


Check  (no  fertilizer) . 
Nitrate  of  soda 


10.01 


In  contrast  to  such  striking  results  from  the  use  of  fertilizers  it 
should  be  mentioned  that  nitrogen,  alone  and  in  combination  with  other 
nutrients,  has  been  applied  to  many  orchards  without  resulting  in  materi- 
ally increased  yields.  Thus  Hedrick  and  Anthony^*^  summarize  the 
results  of  a  20-years'  experiment  in  a  New  York  orchard  as  follows: 
"Adding  acid  phosphate  at  the  rate  of  340  pounds  per  acre  per  year  has 
not  given  a  noticeable  increase  in  yield.     The  addition  of  196  pounds  of 

Table  72i'^^VERAGE  Annual  Results  from  Orchard  Fertilizers  in  Ohio 
(After  Bnllou") 


Treatment 


Average 

yield 
per  tree 
(pounds) 

Average 
gain  per 

acre 
(barrels) 

Value  of 
increase 
per  acre 

Net 
increase 
per  acre 

31.5.6 

67.7 

$169.25 

$163.25 

20.5.8 

37.4 

93 .  .50 

83.50 

93.  S 

6.5 

16.25 

8.25 

214.2 

39.8 

99.50 

91.50 

96.0 

7.2 

18.00 

15.50 

100.1 

8.3 

20.75 

20.75 

69.9 

^vFitrate  of  soda  5  pounds 

Nitrate  of  soda  5  pounds,  acid  phos- 
phate 5  pounds,  muriate  of  potash 
2}4  pounds 

Tankage  5  pounds,  bone  5  pounds, 
muriate  of  potash  5  pounds 

Nitrate  of  soda  5  pounds,  acid  phos- 
phate 5  pounds 

Muriate  of  potash  5  pounds 

Stable  manure  2.50  pounds 

CGhecks  (no  fertilizer) 


muriate  of  potash  to  the  340  pounds  of  acid  phosphate  seems  to  have 
resulted  in  an  increased  yield.  The  annual  application  of  50  pounds  of 
readily  available  nitrogen  in  addition  to  the  phosphoric  acid  and  potash 
has  caused  no  increase  in  yield."  Gourley,^^  likewise,  working  in  New 
Hampshire  with  a  soil  of  entirely  different  character,  obtained  but  slightly 
increased  yields  from  the  use  of  nitrogen  alone  or  in  combination  over 
those  attending  a  clean  cultivation-cover  crop  method  of  soil  management 
without  fertilization.  The  first  of  these  two  investigators  states,  how- 
ever: "An  analysis  of  the  soil  before  the  experiment  was  begun  shows  that 
at  that  time  there  was,  in  the  upper  foot  of  soil,  enough  nitrogen  (total) 


214 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


per  acre  to  last  mature  apple  trees  183  years,  of  phosphoric  acid,  295 
years,  of  potash,  713  years. "^^  Evidently  amounts  of  these  nutrients 
sufficient  for  the  trees'  growth  and  production  were  being  made  available 
year  after  year  by  various  natural  agencies.  'The  second  of  the  two 
investigators,  though  not  reporting  on  the  total  nitrogen  supply  of  the 
soil,  presents  data  to  show  that  the  clean  cultivation-cover  crop  method 
of  management  made  available  each  season  plenty  of  nitrogen,  though 
after  some  years  there  was  some  evidence  that  nitrogen  applications  in 
the  near  future  would  increase  yields. ^"^^  In  the  presence  of  abundant 
supplies  additional  applications  gave  no  increased  yields  worth  mention- 
ing. Interesting  in  this  particular  connection  are  data  presented  in 
Table  73  showing  the  effects  of  various  amounts  of  nitrogen-carrying 
fertilizers  on  yield   of  pears.     The  trees  were  yielding    well    without 

Table  73. — Effects  of  Various  Amounts  of  Nitrogen-carrying  Fertilizers 
ON  Yield  of  Pears 

{After  Reimer^^*) 


1917  treatment 

Yield, 

boxes 

per  tree 

1918  treatment 

Yield, 

boxes 

per  tree 

Check 

12.13 
15.12 
15.45 
16.53 

17.03 
15.06 

Check 

15  00 

10  pounds  nitrate  of  lime  per  tree 

10  pounds  nitrate  of  soda  per  tree 

5  pounds  nitrate  of  soda  per  tree 

10  pounds  nitrate  of  lime  per  tree. .  .  . 
10  pounds  nitrate  of  soda  per  tree 

5  pounds  nitrate  of  soda  and  5  pounds 

superphosphate  per  tree 

18.84 
18.37 

16  63 

5  pounds  nitrate  of  soda  per  tree 

5  pounds  nitrate  of  soda  per  tree 

5  pounds  nitrate  of  soda 

17  72 

5  pounds  sulphate  of  ammonia 

18.23 

fertilizer  applications  but  when  small  amounts  of  quickly  available 
nitrogen  were  applied  they  at  once  responded,  production  apparently 
reaching  a  maximum  (thinning  being  practiced)  for  the  size  of  trees  in 
question.  Applications  of  larger  amounts  of  fertilizer  under  these 
conditions  resulted  in  no  greater  yield.  If  larger  amounts  are  available 
they  are  not  taken  up  or  if  taken  up  they  are  not  used  in  increased  fruit 
production.  It  is  economical  for  the  grower  to  apply  only  such  fertilizers 
in  such  amounts  as  the  tree  can  use  with  profit  to  himself. 

The  Correlation  Between  Vegetative  Growth  and  Yield. — Bearing 
directly  on  the  question  of  the  influence  of  fertilizers,  particularly  nitrog- 
enous fertilizers,  on  yield  and  also  on  that  much  disputed  question  as  to 
whether  vegetative  growth  and  fruit  production  are  antagonistic  tenden- 
cies, are  the  graphs  shown  in  Figs.  25  and  26,  plotted  from  data  on  apple 
yields  and  growth  as  influenced  by  fertilizers  in  Pennsylvania  and  from 
data  on  peach  yields  and  growth  in  West  Virginia.  The  solid  lines  in 
Fig.  25  represent  increase  in  yield  (in  percentages)  resulting  from  the 
use  of  various  fertilizer  combinations.     The  dash-dot  lines  represent 


THE  APPLICATION  OF  NITROGEN-CARRYING  FERTILIZERS    215 

increases  in  vegetative  growth,  figured  in  the  same  way,  length  of  terminal 
shoots  being  taken  as  a  measure  of  vegetative  vigor.  Both  lines  represent 
10-year  averages  of  a  number  of  experiments  on  mature  apple  trees 
growing  under  various  soil  conditions.  Though  these  curves  show  slight 
irregularities,  those  for  increases  in  growth  take  the  same  general  direc- 
tion as  those  for  increases  in  yield.  In  other  words,  as  vegetative  growth 
has  increased,  yields  have  increased,  but  yields  have  increased  much  more 
rapidly  than  vegetative  growth.  This  latter  fact  would  seem  to  prove 
beyond  all  question  not  only  that  increased  vegetative  growth  due  to 
fertilization  is  not  generally  antagonistic  to  heavier  fruit  production,  but 
that  within  limits  it  actually  encourages  heavier  fruiting.  Data  recently 
presented  for  apple  tree  growth  and  yields  in  Delaware  lead  to  the  same 
general  conclusion. ^"^^  Graphs  shown  in  Fig.  26,  made  from  4-year 
averages  for  increases  in  peach  yields  in  West  Virginia  through  fertiliza- 
tion, show  the  same  relationship  between  vegetative  growth  and  yield. 
Here,  though  yields  have  not  quite  kept  pace  with  the  increased  vegeta- 
tive growth,  the  conclusion  is  obvious  that  in  the  peach  increased  wood 
growth  is  associated  with  increased  fruit  production. 

The  same  graphs  showing  the  general  relationship  between  vegetative 
growth  and  yield  also  throw  some  light  on  the  way  in  which  the  fertilizers 
have  increased  production.  Under  the  conditions  of  these  tests  about 
half  of  the  increased  yield  was  due  to  the  greater  wood  growth;  in  other 
words,  to  the  effect  of  the  fertilizer  in  producing  additional  fruit  spurs  and 
fruit-bud-bearing  shoots.  The  other  half  oi  the  increase  was  due  appar- 
ently to  the  greater  activity  of  the  old  spurs.  Presumably  increased 
yield  was  not  obtained  in  the  New  York  and  New  Hampshire  experiments 
to  which  reference  has  been  made  because  the  trees'  nutritive  require- 
ments for  new  wood  growth  were  fully  met  by  the  supply  already  avail- 
able in  the  soil  and  because  they  were  already  producing  heavy  crops. 
That  decreased  yield  often  accompanies  increased  vegetative  growth 
following  the  use  of  nitrogenous  fertilizers  is  indicated  by  results  with 
strawberries  in  Missouri ^^  and  with  red  raspberries  in  New  York." 

Influence  of  Nitrogen  on  Composition  and  on  Season  of  Maturity. — 
The  composition  of  various  plant  tissues,  especially  in  so  far  as  their 
mineral  constituents  are  concerned,  has  been  shown  to  be  influenced 
considerably  by  the  character  of  the  soil  in  which  they  grow.  Their 
composition  would  be  expected,  therefore,  to  show  the  influence  of 
fertilizer  application.  Some  interesting  experimental  data  on  this 
question  have  been  obtained  with  rj'^e,  buckwheat  and  certain  other  crops. 
These  crop  plants  were  grown  in  what  were  considered  normal  media  and 
in  media  possessing  excessive  amounts  of  certain  nutrients.  The  following 
statements  from  the  report  on  these  experiments  may  be  quoted  here:^^ 
"In  general  it  appears  as  if  the  nutrients  actually  required  for  normal 
growth  of  the  crops,  when  there  are  plenty  of  other  ingredients  to  furnish 


216  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

the  indifferent  ash,  need  not  exceed  2.0  per  cent,  of  nitrogen,  1.5  per  cent, 
of  potassium  oxid,  and  0.5  per  cent,  of  phosphoric  oxid ...  In  compar- 
ing excessive  percentages  with  the  foregoing  amounts,  it  may  be  noticed 
that  in  certain  instances  .  .  .  the  percentages  have  increased  to  the 
following  high  magnitudes:  Nitrogen,  3.96  and  potassium  oxide  5.56  in 
1911  in  rye;  and  phosphoric  oxide  1.36  in  1916  in  buckwheat.  Of  course, 
these  amounts  are  much  in  excess  of  what  was  necessary."  The  olive 
has  been  said  to  have  a  higher  oil  content  when  grown  on  a  limestone 
soil.^^^  Presumably  fertilizing  the  olive  orchard  heavily  with  lime  would 
have  some  influence  in  the  same  direction.  Strawberries  on  nitrogen- 
fertilized  plants  have  been  found  to  wilt  more  in  times  of  severe  drought 
than  those  on  unfertilized  plants.-^  Wickson^''^  states:  "Puffiness  of 
oranges  is  clearly  due  in  some  cases  to  excess  of  nitrogenous  manures" 
and  "the  effect  of  excessive  use  of  stable  manures,  or  of  other  manures 
very  rich  in  nitrogen,  upon  the  products  of  the  vine  has  been  frequently 
noted  as  destructive  to  bouquet  and  quality." 

There  are  a  number  of  indirect  ways  in  which  fertilization,  particu- 
larly with  nitrogenous  fertilizers,  influences  composition.  For  example, 
the  use  of  nitrate  of  soda  in  the  apple  orchard  has  been  shown  frequently 
to  result  in  increased  size  of  fruit;  such  differences  in  size  are  often 
correlated  with  differences  in  texture,  in  juiciness  and  in  what  is  generally 
termed  quality.  These  influences  are  not  well  enough  understood, 
however,  to  make  possible  definite  recommendations  for  the  developing 
of  certain  quahties  or  substances,  as  sugar  or  acid  or  pectins,  through  the 
use  of  fertilizers.  Often  resistance  or  susceptibility  to  certain  diseases  is 
closely  correlated  with  the  chemical  composition  of  the  tissues  subject  to 
invasion  and  even  a  slight  change  in  composition  that  might  be  brought 
about  either  directly  or  indirectly  through  the  use  of  some  fertilizer  might 
be  of  great  use  in  reducing  injury  from  the  invading  parasite  or  its  toxin. 

The  effect  of  nitrogenous  fertilizers  on  season  of  maturity  of  the 
wood  has  been  mentioned.  In  the  section  on  Temperature  Relations 
it  is  shown  that  the  breaking  of  the  winter  rest  period  in  certain  fruits 
is  closely  correlated  with  the  time  of  maturing  of  the  wood  in  the  fall 
and  in  turn  susceptibility  to  low  temperatures  in  late  winter  is  associated 
with  the  breaking  of  the  rest  period.  Thus,  indirectly,  applications 
of  nitrogen  may  have  an  important  influence  on  certain  forms  of  winter 
injury.  Indeed  the  peach  and  some  other  fruits  are  probably  grown 
sometimes  under  conditions  where  fertilization  with  nitrogen-carrying 
materials  may  be  profitable  for  this  reason  if  for  no  other. 

Application  of  nitrate  of  soda  has  delayed  the  ripening  of  peaches 
in  West  Virginia  from  1  week  to  10  days,  the  delay  being  greater  in 
the  later  varieties.^  Observations  elsewhere  indicate  that  almost  any 
material  carrying  quickly  available '  nitrogen  has  a  similar  influence 
on  many  other  fruits. 


THE  APPLICATION  OF  NITROGEN-CARRYING  FERTILIZERS    217 

In  a  later  chapter  it  is  shown  that,  within  certain  Hmits,  the  plant 
shows  very  much  the  same  response  to  certain  kinds  of  pruning  as  it 
does  to  apphcations  of  nitrogen-carrying  fertihzers.  In  other  words  it  is 
possible  within  certain  Hmits  to  accomplish  by  proper  fertilization 
results  comparable  to  those  produced  by  pruning.  This  is  true  par- 
ticularly in  the  effects  of  these  two  practices  on  new  shoot  and  leaf  growth, 
on  the  better  setting  of  fruit  and  on  the  size  of  fruit.  Probably  for 
best  results  there  should  be  a  judicious  combination  of  both  practices. 
For  commercial  production,  however,  it  will  often  be  found  more  practic- 
able to  reduce  the  pruning  to  a  minimum  and  to  depend  rather  on 
fertilization.  Fertilizers  are  comparatively  cheap  and  they  are  quickly 
and  easily  applied.  On  the  other  hand  pruning  that  is  properly  done 
requires  considerable  judgment  and  skill  and  is  comparatively  expensive. 
To  the  extent  that  the  same  results  can  be  obtained  by  the  two  methods, 
much  greater  profits  will  be  realized  from  the  investment  in  fertilizers. 

Summary. — In  many  cases  the  use  of  quickly  available  nitrogenous 
fertilizers  in  the  orchard  has  resulted  promptly  in  considerably  increased 
vegetative  growth,  the  response  being  evident  in  longer  shoots  and  in 
greater  numbers  of  leaves  that  are  larger  in  size  and  darker  in  color 
than  those  of  unfertilized  trees.  For  the  most  part  these  responses 
have  been  made  by  trees  recently  showing  a  lack  of  vegetative  vigor, 
trees  most  likely  to  be  found  in  sod  land  or  in  infertile  soils.  On  the 
other  hand  there  has  been  little  evidence  of  increased  vegetative  growth 
from  the  application  of  such  fertilizers  to  moderately  rich  soils  in  which 
the  trees  are  already  making  a  good  growth.  In  many  orchards,  therefore 
nitrogen  is  not  a  limiting  factor  to  growth  and  in  those  where  marked 
responses  are  obtained  from  moderate  applications,  larger  applications 
often  evoke  no  greater  response.  Increased  blossom  bud  formation 
often  accompanies  the  increased  vegetative  growth  that  follows  the 
use  of  nitrogenous  fertilizers.  Fruit  setting  in  trees  showing  poor  vege- 
tative vigor  is  greatly  increased.  The  size  of  the  fruit  may  be  decreased 
or  increased  by  the  use  of  nitrogenous  fertilzer  depending  on  whether  water 
is  a  limiting  factor.  The  correlation  between  the  amount  of  new  vegeta- 
tive growth  and  fruit  size  is  generally  positive  but  not  high.  Yield,  which 
is  a  product  of  fruit  bud  formation,  fruit  setting  and  subsequent  develop- 
ment, naturally  is  often  increased  greatly  by  nitrogen  applications. 
The  development  of  the  red  color  of  many  fruits  is  somewhat  checked 
by  the  use  of  nitrogenous  fertilizers  because  of  the  heavier  shade  incident 
to  the  increased  vegetative  growth.  Within  fairly  wide  limits  fruit 
production  is  found  to  increase  with  an  increase  in  vegetative  vigor. 
The  general  effect  of  nitrogenous  fertilizers  is  to  delay  maturity  of 
both  wood  and  fruit.  Though  some  influence  is  shown  on  the  composi- 
tion of  the  fruit,  in  most  cases  this  is  of  secondary  importance. 


CHAPTER  XIII 
FERTILIZERS,  OTHER  THAN  NITROGENOUS,  IN  THE  ORCHARD 

The  conclusion  should  not  be  drawn  from  the  statements  in  pre- 
ceding chapters  that  in  practice  only  nitrogenous  fertilizers  are  of  value 
in  the  deciduous  fruit  plantation.  A  single  instance  in  which  a  favorable 
response  attended  the  use  of  some  other  fertilizer  would  indicate  that 
the  problem  should  be  considered  from  other  points  of  view;  there  are 
many  such  instances. 

The  Indirect  Effects  of  Fertilizers. — Repeated  reference  has  been 
made  to  the  direct  and  possibly  indirect  effects  of  fertilizers  on  the  solu- 
biUty  or  availabihty  of  other  soil  ingredients,  on  soil  reaction,  or  on  the 
plants  that  constitute  the  mulch  or  the  cover  crop.  Without  doubt 
this  last  mentioned  influence  is  one  of  the  most  important,  especially 
in  orchards  not  under  clean  cultivation.  In  either  a  sod-  or  grass-mulch 
or  a  cover-crop  method  of  culture  the  vegetation  produced  between  the 
trees  is  returned  to  the  soil.  Only  those  mineral  constituents  are 
returned  that  are  obtained  from  the  soil,  but  in  every  case  there  is  added 
a  considerable  amount  of  organic  matter  which,  through  its  effect  on  soil 
texture  and  water-holding  capacity  as  well  as  through  the  chemical  effects 
of  its  decomposition  products,  plays  a  very  important  part  in  the  general 
aspect  of  productivity;  with  leguminous  crops  the  nitrogen  supply  is 
actually  augmented.  Furthermore  the  mineral  constituents  may  be  so 
changed  in  form  by  these  intercrops  as  to  be  much  more  available  to  the 
crop  plants.  It  is  generally  considered  that  the  value  of  these  inter- 
cultures  is  more  or  less  directly  proportional  to  the  amounts  of  vegetation 
produced.  If  this  is  the  case  any  soil  treatment  or  fertilizer  which  results 
in  an  increased  growth  of  the  interculture  may  be  of  indirect  benefit  to 
the  tree.  As  a  rule  these  crop  plants  grown  between  the  trees  are  greatly 
helped  by  apphcations  of  nitrogen-carrying  fertilizers  made  primarily 
for  the  trees'  direct  and  immediate  use.  Under  such  circumstances  the 
trees  consequently  receive  a  double  benefit  from  their  application,  an 
immediate  benefit  from  such  portions  as  they  are  able  to  absorb  before 
it  leaches  away  or  is  used  by  the  other  plants  and  a  deferred  benefit 
realized  only  when  these  plants  decay. 

Phosphoric  Acid. — Phosphoric  acid  is  frequently  of  much  indirect 
benefit  to  orchard  trees.  Some  measure  of  this  influence  may  be  obtained 
from  data  presented  in  Table  74,  for  an  orchard  under  the  sod-mulch 
method  of  management  in  southern  Ohio.  Acid  phosphate  alone  in- 
creased the  yield  of  mulching  material  more  than  threefold  and  a  so- 

218 


FERTILIZERS,  OTHER  THAN  NITROGENOUS 


219 


Table  74. — Effects  of  Certain  Fertilizers  on  the  Production  of   Mulching 

Material 
{After  Ballon'') 


Annual  fertilizer  treatment  per  acre 


Kind  of  cover  crop 


Acid  phosphate  350  pounds 

Acid  phosphate  350  pounds,  muriate  of 
potash  175  pounds 

Acid  phosphate  350  pounds,  muriate  of 
potash  175  pounds,  nitrate  of  soda  350 
pounds 

Unfertilized 


Red  clover 
Red  clover 


Timothy,  red  top,  blue  grass 
Poverty  grass,  weeds 


called  complete  fertilizer  increased  it  over  fourfold.  Of  equal  signifi- 
cance was  the  change  effected  in  the  nature  of  the  dominant  vegetation. 
The  unfertilized  areas  are  reported  as  covered  with  a  thin  growth  of 
poverty  grass  and  weeds. ^  When  these  areas  were  fertilized  with  nitrate 
of  soda  alone  or  when  that  material  was  used  in  large  quantities  in  com- 
bination with  other  fertilizers,  timothy,  redtop,  bluegrass  and  orchard 
grass  rapidly  took  the  place  of  the  weeds  and  poverty  grass.  When 
acid  phosphate  was  used  alone  or  in  combination  with  potash,  clover 
came  in  thickly  and  crowded  out  the  grasses.  The  ground  was  stocked 
with  all  of  these  species  before  any  fertilizer  was  applied.  The  effect 
of  the  different  applications  was  simply  to  furnish  one  group  or  another 
with  conditions  particularly  suitable  for  its  growth  while  the  plants  of 
the  other  group  remained  small  and  stunted.  This  effect  is  particularly 
interesting  in  the  case  of  the  acid  phosphate,  as  the  clover  whose  develop- 
ment it  made  possible  is  a  nitrogen  gatherer  and  thus  the  application  of 
phosphorus  would  result  ultimately  in  an  increased  nitrogen  supply  for 
the  trees.  Probably  it  w^ould  not  be  safe  to  recommend  generally  the 
maintenance  of  the  nitrogen  supply  in  the  orchard  through  the  use  of 
acid  phosphate,  but  there  are  conditions  where  such  a  method  of  pro- 
cedure might  be  entirely  practicable  and  there  are  probably  many  other 
orchards  in  which  it  would  be  desirable  to  supplement  nitrogen-carrying 
fertilizers  with  those  carrying  phosphorus. 

Sulphur. — Similarly  there  is  reason  to  believe  that  vegetative  growth 
and  production  maybe  increased  by  the  use  of  sulphur-carrying  fertilizers, 
even  though  the  soil  may  contain  a  supply  of  available  sulphur  well  in 
excess  of  the  trees'  actual  requirements.  Elsewhere  in  this  section  it  is 
stated  that  in  certain  fruit-growing  sections  sulphur  is  a  limiting  factor 
for  the  growth  of  leguminous  intercultures,  especially  alfalfa.  In  such 
cases  the  judicious  use  of  sulphur-carrying  fertilizers  may  have  a  far-reach- 


220  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

ing  influence  on  the  trees,  though  they  themselves  may  not  be  able  to 
use  any  of  it.  The  good  results  frequently  obtained  from  the  use  of 
acid  phosphate  and  credited  to  the  influence  of  the  phosphorus  may  be 
due  in  part  to  the  sulphur  carried  by  that  fertilizer. 

This  question  of  the  influence  of  different  fertilizer  treatments  on  the 
nature  of  the  plant  population  in  undisturbed  soil  has  been  studied  very 
carefully  at  the  Rothamstead  Experimental  Station  in  England.  Differ- 
ences are  to  be  expected  with  varying  soil  conditions  and  without  doubt 
the  response  in  an  orchard  would  be  different  from  that  in  an  open  meadow 
such  as  that  in  which  the  Rothamstead  investigations  were  conducted. 
Nevertheless  the  following  statement  from  the  summary  of  this  work 
is  very  suggestive: 

"In  the  produce  grown  continuously  without  manure  the  average  number  of 
species  found  has  been  49.  Of  these,  17  are  grasses,  four  belong  to  the  order 
Leguminosfe,  and  28  to  other  orders.  The  percentage,  by  weight,  of  the  grasses 
has  averaged  about  68,  that  of  the  Leguminosae  about  nine,  and  that  of  species 
of  other  orders  about  23. 

"In  the  produce  of  the  plot  already  referred  to  as  the  most  heavily  manured, 
and  yielding  the  heaviest  crops,  the  average  number  of  species  found  has  been 
only  19,  of  which  12  to  13  are  grasses,  one  only  (or  none)  leguminous,  and  five  to 
six  only  represent  other  orders;  whilst  the  average  proportions  by  weight  have 
been — of  grasses  about  95  per  cent.,  of  Leguminosse  less  than  0.01  per  cent.,  and 
of  species  representing  other  orders  less  than  5  per  cent. 

"On  the  other  hand,  a  plot  receiving  annually  manures  such  as  are  of  little 
avail  for  gramineous  crops  grown  separately  in  rotation,  but  which  favor  beans 
or  clover  so  grown,  has  given,  on  the  average,  43  species.  Of  these,  17  in  number 
are  grasses,  four  Leguminosse,  and  22  belong  to  other  orders,  but  by  weight,  the 
percentage  of  grasses  has  averaged  only  65-70,  that  of  the  Leguminosae  nearly 
20,  and  that  of  species  belonging  to  other  orders  less  than  15.    .    .    . 

"It  is  found  that  there  is  a  considerable  difference  in  the  percentage  of  dry 
substance  in  the  produce,  and  very  considerable  difference  in  the  percentage  of 
mineral  matter  (ash)  in  that  dry  substance.  There  is  still  greater  difference  in 
the  percentage  of  nitrogen  in  the  dry  matter,  and,  again,  a  greater  difference  still 
in  the  percentage  of  individual  constituents  of  the  ash.  When,  indeed,  it  is 
remembered  that  a  plot  may  have  from  20  to  50  different  species  growing  upon 
it,  each  with  its  own  peculiar  habit  of  growth,  and  consequent  varying  range  and 
power  of  food-collection,  it  will  not  appear  surprising  that  different  species  are 
developed  according  to  the  manure  employed;  and,  this  being  so,  that  the  charac- 
ter and  amount  of  the  constituents  taken  up  from  the  soil  by  such  a  mixed  herb- 
age should  be  found  much  more  directly  dependent  on  the  suppUes  of  them  by 
manure  than  is  the  case  with  a  crop  of  a  single  species  growing  separately. 

"In  further  illustration  it  may  be  mentioned  that,  not  only  does  the  per- 
centage of  nitrogen  in  the  dry  substance  of  the  produce  of  the  different  plots 
vary  considerably,  but  the  average  annual  amount  of  it  assimilated  over  a  given 
area  is  more  than  three  times  as  much  in  some  cases  as  in  others.  Again,  the 
percentage  of  potash  in  the  dry  substance  is  three  times  as  much  in  some  cases 


FERTILIZERS,  OTHER  THAN  NITROGENOUS  221 

as  in  others;  whilst  the  difference  in  the  average  annual  amount  of  it  taken  up 
over  a  given  area  is  more  than  five  times  as  much  on  some  plots  as  on  others — 
dependent  on  the  supplies  of  it  by  manure,  and  the  consequent  description  of 
plants,  and  amount,  and  character,  of  growth  induced.  The  percentage  and 
acreage  amounts  of  phosphoric  acid  also  vary  very  strikingly;  and  ao  again  it  is 
with  other  mineral  constituents,  but  in  a  less  marked  degree.""* 

Li7ne. — Calcium  has  been  mentioned  as  an  element  practically  always 
present  in  quantities  far  greater  than  orchard  trees  require.  Indeed 
very  large  amounts  are  likely  to  lead  to  chlorotic  conditions  through  mak- 
ing the  soil  reaction  alkaline  and  thus  rendering  iron  unavailable.  Never- 
theless liming  the  soil  accelerates  nitrification  and  may  thus  indirectly 
help  the  orchard  plants  to  obtain  a  larger  supply  of  nitrogen.  The 
strawberry  has  been  mentioned  particularly  as  a  plant  preferring  an  acid 
soil  and  as  being  actually  harmed  by  applications  of  lime.  Yet  it  is 
common  experience  that  strawberries  do  exceptionally  well  following 
clover,  though  clover  is  very  sensitive  to  acid  soils  and  usually  profits 
greatly  from  liming.  In  this  case  it  is  entirely  practicable  to  apply  lime 
to  the  clover  field  a  year  before  the  sod  is  turned  under  for  the  strawberry 
plants.  The  lime  stimulates  the  growth  of  the  clover  and  its  effect  on 
soil  reaction  wall  have  largely,  if  not  wholly,  disappeared  by  the  time  the 
ground  is  ready  for  the  strawberries.  Ultimately  the  strawberries  will 
profit  greatly  from  the  lime  applied  to  the  clover  that  preceded  them, 
though  its  direct  application  would  result  in  serious  injury. 

Illustrations  might  be  given  of  other  indirect  influences  of  fertilizers, 
but  enough  has  been  said  here  and  at  other  places  in  this  section  to  afford 
some  idea  of  the  many  ways  in  which  they  may  affect  orchard  trees. 
Enough  has  been  said,  also,  to  make  it  clear  that  these  indirect  are  often 
as  important  as  the  direct  influences,  for  there  may  be  no  occasion  to 
supply  the  plant  with  more  nutrients.  With  our  present  knowledge  it 
is  impossible  to  predict  with  certainty  all  of  the  effects,  direct  and 
indirect,  that  any  particular  fertilizer  will  have  in  a  given  orchard.  How- 
ever, this  should  not  prevent  the  careful  study  of  each  situation  as  it 
arises. 

Plant  Nutrient  Carriers ;  Different  Forms  of  Fertilizers. — The  neces- 
sity that  the  different  plant  nutrients  be  in  certain  forms  if  they  are 
to  be  taken  up  by  the  tree  has  been  discussed  under  the  subjects  of  Solu- 
bility and  Availability  in  Chapter  VII.  This  does  not  mean,  however, 
that  fertilizers  must  contain  these  elements  in  these  particular  forms, 
for  as  soon  as  applied  they  become  subject  to  numerous  changes  through 
the  physical,  chemical  and  biological  factors  always  at  work  in  the  soil. 
Nevertheless  there  are  certain  advantages  and  certain  disadvantages 
inherent  in  different  fertilizers  because  of  the  form  in  which  they  carry 
the  elements  for  which  they  are  valued.  A  brief  discussion  of  this  matter 
as  it  applies  to  orchard  problems  is  included  at  this  point. 


222  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Nitrogen  from  Inorganic  Sources. — The  more  common  of  the  nitrogen- 
carrying  commercial  fertilizers  are  nitrate  of  soda,  sulphate  of  ammonia 
and  dried  blood.  Only  the  first  of  these  three  materials  contains  nitrogen 
in  a  form  in  which  it  is  used  in  any  considerable  amounts  by  most  plants. 
It  is  therefore  one  of  the  most  readily  available  forms  of  nitrogen,  though 
the  nitrogen  of  the  other  two  materials  soon  becomes  available.  The 
first  two  of  these  fertihzers  are  readily  soluble  in  water  and  in  the  soil 
solution;  dried  blood  is  less  soluble.  This  at  once  raises  the  practical 
question  of  loss  through  leaching.  Some  expression  of  the  differences 
between  these  fertilizers  in  this  respect  as  well  as  in  their  rates  of  avail- 
ability is  obtained  from  an  investigation  on  a  light  sandy  loam  in 
Florida. ^^  The  report  on  this  investigation  states:  "For  the  period  from 
July  13,  1911,  to  July  17,  1913,  41  per  cent,  of  the  sulphate  of  ammonia 
applied  to  the  soil  leached  thru  and  was  lost  in  the  drainage  water; 
72.5  per  cent,  of  the  nitrate  of  soda,  and  38.3  per  cent,  of  the  dried  blood 
were  lost.  .  .  .  The  larger  loss  of  nitrate  of  soda  is  explained  by  the 
fact  that  this  material  is  very  readily  soluble  in  the  soil  moisture  and  that 
the  soil  has  very  little  if  any  power  to  retain  or  fix  nitrogen  in  the  nitrate 
form.  ...  In  its  original  form  the  nitrogen  of  dried  blood  is  not  readily 
soluble  in  the  soil  water,  and  consequently  very  little  is  lost  in  the  leaching 
process  until  nitrification  occurs.  In  this  change  the  organic  nitrogen 
of  the  blood  is  changed  first  to  ammonia,  then  to  the  nitrite  and  finally 
to  the  nitrate  form,  when  it  becomes  as  readily  soluble  as  the  nitrate  of 
soda  and  is  leached  out  as  readily.  Nitrification  of  the  dried  blood  is  a 
gradual  process,  extending  over  a  period  of  time  which  may  be  of  several 
weeks'  duration,  depending  on  soil  conditions.  Because  of  this,  some  of 
the  nitrogen  of  dried  blood,  or  for  that  matter,  any  similar  organic  mate- 
rial, will  remain  in  the  soil  a  considerably  longer  time  and  be  available 
to  the  crop  over  a  longer  period  than  nitrate  of  soda.  This  is  especially 
true  where  heavy  rains  occur  after  the  latter  has  been  applied  to  the 
soil.  .  .  .  While  sulphate  of  ammonia  is  readily  soluble  in  the  soil  water 
the  soil  has  the  power  of  fixing  or  absorbing  at  least  a  portion  of  the 
ammonia,  thus  preventing  it  from  leaching  away.  This  takes  place 
through  chemical  means  and  is  common  to  all  soils.  Very  sandy  soils 
can  absorb  only  a  small  amount  of  ammonia;  loam  and  clay  soils  are  able 
to  absorb  much  larger  quantities." 

Attention  may  be  called  also  to  the  opposite  influences  of  nitrate  of 
soda  and  sulphate  of  ammonia  on  soil  reaction.  In  the  former  the 
nitrogen  is  combined  with  a  basic  and  in  the  latter  with  an  acid  radical. 
As  the  nitrogen  is  used  by  the  plants  the  soil  is  gradually  rendered  more 
basic  in  the  first  instance  and  more  acid  in  the  second ;  in  the  latter  case 
the  sulphate  generally  combines  with  calcium,  resulting  ultimately  in  a  loss 
of  this  element  from  the  soil  through  leaching.  CoUison^^  has  found  that 
in  some  soils  this  loss  of  calcium  when  sulphate  of  ammonia  is  used  as  a 


FERTILIZERS,  OTHER  THAN  NITROGENOUS  223 

fertilizer  amounts  to  over  twice  that  taking  place  when  nitrate  of  soda 
is  appHed.  The  change  in  soil  reaction  occasioned  by  one  or  two  succes- 
sive applications  of  the  same  material  would  seldom  be  large  enough 
to  have  great  practical  importance  in  the  orchard,  but  since  the  effects 
are  cumulative  repeated  applications  for  many  years  might  conceivably 
result  in  injury  to  the  trees.  The  remedy  for  this  situation  is  the  use  first 
of  the  nitrate  of  soda  and  then  of  the  sulphate  of  ammonia,  keeping  the 
soil  reaction  about  as  it  is  at  the  outset. 

Attention  should  be  called  to  the  inconsequential  difference  obtained 
in  actual  field  trials  from  the  use  of  these  nitrogen-carrying  fertilizers 
when  nitrogen  is  the  limiting  factor  and  when  amounts  are  used  carrying 
approximately  the  same  quantities  of  nitrogen.  Nitrate  of  calcium 
has  been  emploj^ed  occasionally  as  a  fertilizer  in  an  experimental  way  and 
the  response  has  not  differed  materially  from  that  to  nitrate  of  soda. 

The  diiferent  influences  of  these  nitrogenous  fertilizers  on  the  inter- 
cultures  in  the  orchard  may  be  of  greater  significance  than  the  differences 
in  their  direct  influence  on  the  trees.  The  acidic  influence  of  the  sulphate 
of  ammonia  is  likely  to  increase  gradually  the  growth  of  certain  species 
like  bluegrass,  timothy,  redtop  and  orchard  grass  and  to  decrease  the 
growth  of  the  clovers  and  certain  other  legumes.  The  basic  influence  of 
the  nitrate  of  soda  has  the  opposite  effect.  This  is  brought  out  strik- 
ingly by  work  at  the  Rothamstead  Experimental  Station'^o  extending 
over  a  period  of  30  years.  Therefore  if  certain  leguminous  cover  crops 
are  to  be  grown  or  more  especially  if  it  is  desired  to  keep  the  orchard  in  a 
permanent  clover  or  alfalfa  sod,  some  caution  should  be  exercised  in  the 
use  of  sulphate  of  ammonia.  Sodium,  calcium  or  potassium  nitrates  could 
be  used  more  safely. 

The  results  of  many  investigations^""  with  field  crops  indicate  that  a 
given  quantity  of  nitrogen  in  the  form  of  nitrate  of  soda  has  a  greater 
influence  than  the  same  amount  carried  in  many  other  fertilizers.  That 
is,  it  has  more  crop  producing  power  when  held  in  one  form  than  in 
another.  Furthermoi'e  this  relative  efficiency  varies  with  many  factors, 
such  as  the  kind  of  crop  plant  and  the  character  of  the  soil.  Presumably 
this  varying  crop  producing  power  is  associated  with  secondary  or  indirect 
effects  that  the  fertilizer  or  its  disintegration  products  may  have  on  the 
plant  through  their  influence  on  soil  reaction,  the  availability  of  other  soil 
constituents  and  many  other  soil  conditions  and  processes.  Very  little 
is  known  regarding  the  varying  crop-producing  value  of  nitrogen  qarried 
in  different  fertilizers  when  they  are  used  on  fruits. 

Nitrogen  from  Organic  Sources. — A  word  should  be  said  regarding  the 
use  of  certain  nitrogen-carrying  organic  fertilizers.  Barnyard  compost 
and  green  manuring  crops  have  been  recommended  often  as  the  best 
sources  of  nitrogen  for  the  orchard.  There  can  be  no  doubt  but  that 
they  are  effective  fertilizers  when  nitrogen  is  a  limiting  factor,  often 


224  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

yielding  returns  greater  than  those  obtained  from  commercial  fertilizers 
used  in  quantities  carrying  equal  amounts  of  nitrogen.  However,  a  part 
of  their  beneficial  influence  is  without  doubt  due  to  other  nutrients  that 
they  carry  and  to  the  effects  on  the  physical  condition  of  the  soil. 

Thus  Schreiner  and  Shorey/^"  in  discussing  the  physical  condition  of 
the  soil  as  affected  by  organic  matter,  state:  ''The  organic  matter  may, 
and  in  fact  generally  does,  play  an  intimate  part  in  the  behavior  of  the 
mineral  particles,  entering  into  chemical  combination,  coating  them  or 
cementing  them  together.  The  organic  matter  becomes,  therefore,  of 
the  greatest  importance  in  its  influence  on  the  great  controlling  factors  in 
crop  production,  such  as  the  solubility  of  the  soil  minerals,  the  physical 
structure  of  the  soil  granules,  and  the  water-holding  power  of  soils.  To 
illustrate  this,  there  was  found  in  California  a  soil  which  could  not  be 
properly  wetted,  either  by  rain,  irrigation,  or  movement  of  water  from 
the  subsoil,  with  the  result  that  the  land  could  not  be  used  profitably 
for  agriculture.  On  investigation  it  was  found  that  this  peculiarity  of 
the  soil  was  due  to  the  organic  matter,  which  when  extracted  had  the  prop- 
erties of  a  varnish,  repelling  water  to  an  extreme  degree.  The  soil, 
once  freed  of  this  ingredient,  had  a  high  water-holding  power." 

Some  suggestion  of  the  many  ways,  direct  or  indirect,  in  which  organic 
matter  affects  tree  growth  and  production  may  be  derived  from  the  follow- 
ing statements  pertaining  to  the  rosette  of  pecans:  "The  experimental 
and  other  evidence  indicates  very  strongly  that  pecan  rosette  is  a  sign  of  a 
soil  deficient  in  humus,  fertihty,  and  moisture  supply,  .  .  .  The 
constant  addition  of  large  quantities  of  humus-forming  materials,  thereby 
both  bettering  the  physical  condition  of  the  soil  and  increasing  its  water- 
holding  capacity  and  fertility,  is  absolutely  necessary  to  produce  healthy 
trees  from  those  already  diseased  and  to  prevent  the  development  of 
new  cases  of  rosette.  .  .  .  some  consistent  and  definite  soil-building 
policy  should  be  adopted  in  the  pecan  orchards  of  the  South  if  rosette 
is  to  be  overcome  and  healthy  productive  orchards  maintained.  The 
program  of  work  should  involve  the  growing  of  one  crop,  preferably  a 
legume,  which  may  be  returned  to  the  soil.  ...  In  these  experiments, 
heavy  applications  of  stable  manure,  cottonseed  meal  and  stable  manure, 
and  cottonseed  meal  alone,  in  connection  with  legumes,  have  proved 
highly  beneficial  to  rosetted  trees." ^^^  Though  in  cases  like  this  it  is 
impossible  at  present  to  distinguish  between  the  influence  of  the  nitrogen 
and  that  of  the  other  components  of  the  organic  matter  there  is  no  reason 
for  minimizing  their  combined  effects  or  for  failing  to  resort  freely  to  the 
use  of  organic  fertilizers  in  orchard  practice  where  observation  and  experi- 
ence indicate  that  they  may  be  of  decided  benefit.  The  nitrogen  of 
organic  fertilizers  is  more  slowly  available  than  that  of  the  common 
nitrogenous  commercial  fertilizers  and  experience  shows  that  for  quick 
results  the   commercial  sources  are  more   satisfactory.     Investigation 


FERTILIZERS,  OTHER  THAN  NITROGENOUS  225 

shows  that  the  nitrogen  of  both  barnyard  manure  and  of  green  manure 
crops  plowed  under  in  April  or  May  becomes  available  only  gradually  for 
plant  growth  during  the  latter  half  of  the  growing  season.-"^ 

Phosphorus. — Though  experiments  have  shown  little  or  no  direct 
benefit  to  deciduous  fruits  from  the  application  of  phosphatic  fertilizers 
these  are  often  useful  in  stimulating  the  growth  of  intercultures  or  in 
promoting  desirable  changes  and  reactions  in  the  soil. 

The  leading  phosphatic  fertilizers  available  for  use  in  the  orchard  are 
rock  phosphate  or  "floats,"  acid  phosphate  or  superphosphate  and  ground 
bone.  The  phosphorus  in  raw  rock  phosphate  or  "floats"  and  in  ground 
bone  is  held  in  the  form  of  tri-calcium  phosphate,  which  is  very  nearly 
insoluble  in  water  or  in  the  soil  solution  and  hence  becomes  available  for 
plant  growth  very  slowly  as  it  is  acted  upon  gradually  by  various  soil 
agencies.  The  phosphorus  of  acid  phosphate  or  superphosphate  is  held 
as  mono-calcium  phosphate,  which  is  soluble  and  is  the  form  in  which 
plants  are  supposed  to  absorb  most  of  their  phosphorus.  When  added 
to  the  soil  it  unites  with  more  calcium  to  form  di-calcium  or  "reverted" 
phosphate  which  is  intermediate  in  solubility  between  the  mono-  and 
tri-calcium  compounds.  Gradually  this  di-calcium  phosphate  unites 
with  more  calcium  to  form  tri-calcium  phosphate  and  it  finally  exists  in 
the  soil  in  the  same  form  as  in  raw  rock  phosphate.  For  this  reason 
"floats"  or  raw  rock  phosphate  might  be  inferred  to  have  equal  value  with 
the  acid  phosphate  as  a  fertihzer.  This  is  not  the  case,  however,  since 
the  acid-treated  material,  being  readily  soluble,  goes  down  into  the  soil 
and  becomes  fairly  evenly  distributed  throughout  the  area  reached  by 
the  roots.  Furthermore,  the  plants  are  able  to  obtain  considerable  quan- 
tities before  it  becomes  "reverted"  or  certainly  before  it  is  changed  to 
the  very  nearly  insoluble  tri-calcium  form.  Mention  may  be  made  again 
of  the  possibihty  that  some  of  the  benefit  from  acid  phosphate  is  due  to  the 
sulphur  that  it  carries  as  well  as  to  the  phosphorus.  Unlike  nitrogen, 
phosphorus  is  not  lost  from  the  soil  in  large  quantities  through  leaching. 
The  reasons  for  this  have  been  brought  out  in  the  preceding  discussion. 
Some  indication  of  the  phosphorus  fixing  power  of  soil  is  afforded  by  an 
experiment  with  a  light  sandy  loam  in  Florida  m  which  it  was  found  that 
at  the  end  of  four  years  only  0.05  per  cent,  of  the  amount  applied  in 
fertilizers  had  been  lost  through  the  drainage  water,  i"^" 

Potassium. — Though  there  are  a  number  of  different  forms  in  which 
potassium  may  be  applied,  the  two  most  common  are  the  muriate  and  the 
sulphate.  Where  these  two  forms  of  potash  have  been  used  side  by  side 
in  the  fruit  plantation  the  sulphate  has  usually,  though  not  always,  given 
more  striking  results.  The  suggestion  may  be  repeated  that  when  there 
is  an  apparent  need  of  potash  fertihzers,  as  indicated  by  a  material 
response  from  the  use  of  the  sulphate,  the  possible  need  of  sulphur  be 
thoroughly  investigated.     In  marked  distinction  to  the  case  afforded  by 


226  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

phosphorus  we  have  but  httle  evidence  of  an  indirect  benefit  to  the  trees 
through  any  increased  growth  of  the  intercultures  resulting  from  the  use 
of  potash-carrjang  fertihzers. 

Sulphur. — Too  httle  evidence  on  the  use  of  sulphur-carrying  fertilizers 
in  the  orchard  is  available  to  warrant  an  extended  discussion  of  the  differ- 
ent forms  in  which  it  may  be  applied.  Evidently  many  different  forms 
are  eligible,  for  it  has  resulted  in  increased  yields  of  certain  orchard  inter- 
cultures when  used  in  the  form  of  both  potassium  sulphate  and  calcium 
sulphate  (gypsum)  and  increased  grape  yields  have  been  reported  from 
the  use  of  both  gypsum  and  flowers  of  sulphur. ^^  Indeed  it  has  been 
noted  that  alfalfa  and  certain  other  legumes  have  been  greatly  benefited 
from  the  sulphur  contained  in  the  lime-sulphur  spray,  which  had 
dripped  from  sprayed  trees  or  had  drifted  to  the  ground  in  the  process 
of  spraying. 

Lime. — Though  calcium  is  one  of  the  elements  essential  for  the  growth 
of  plants,  the  point  has  been  made  that  there  are  but  few  soils  to  which 
its  application  in  fertilizers  is  desirable  for  the  purpose  of  supplying  the 
tree  directlj'^  with  additional  amounts  and  though  there  are  indirect  ways 
in  which  it  may  frequently  benefit  orchard  trees,  there  are  indirect  ways 
in  which  it  may  also  injure  them.  The  data  that  have  been  presented 
make  it  clear,  furthermore,  that  the  same  plant  may  be  either  benefited 
or  injured  by  liming,  according  to  the  condition  of  the  soil.  That  there 
are  marked  differences  between  species — and  even  varieties  of  the  same 
species — in  their  tolerance  of  lime  or  their  tolerance  of  the  soil  basicity 
with  which  it  is  likely  to  be  associated  or  in  their  response  to  lime  applica- 
tions, should  be  emphasized.  The  results  of  work  at  the  Rhode  Island 
Experiment  Station  may  be  cited.  Those  results  have  been  summarized 
as  follows: "According  to  experiments  made  by  the  Rhode  Island  Agri- 
cultural Experiment  Station  on  acid  soils  in  that  State,  the  plants  tested 
may  be  classified  with  regard  to  their  behavior  toward  lime  as  follows: 
Plants  benefited  by  liming:  .  .  .  alfalfa,  clover  (red,  white,  crimson 
and  alsike)  .  .  .  oats,  timothy,  Kentucky  bluegrass,  Canada  pea, 
Cuthbert  raspberry,  gooseberry,  currant  (white  Dutch),  Orange  quince, 
cherry,  Burbank  Japan  plum,  American  linden  .  .  .  plants  but  little 
benefited  by  liming  .  .  .  rye,  .  .  .  Rhode  Island  bent,  and  redtop; 
plants  slightly  injured  by  liming  .  .  .  Concord  grape,  peach,  apple, 
and  pear;  plants  distinctly  injured  by  liming  .  .  .  velvet  bean,  .  .  . 
blackberry,  black-cap  raspberry,  cranberry,  Norway  spruce,  and  Amer- 
ican white  birch.  Other  plants  said  to  be  injured  are  the  chestnut, 
azalea,  and  rhododendron." ^^^ 

Another  point  that  may  be  mentioned  in  connection  with  the  appli- 
cation of  lime  is  that  there  is  little  occasion  to  use  it  in  the  fruit  plantation 
for  flocculation  purposes.  Soils  with  a  texture  so  impervious  that  the 
flocculating  effects  of  lime  are  needed  to  promote  drainage  and  aeration 


FERTILIZERS,  OTHER  THAN  NITROGENOUS  227 

are  generally  too  poorly  suited  to  fruit  production,  even  with  the  aid  of 
such  palliative  measures  as  liming. 

Season  for  Applying  Fertilizers. — Comparatively  few  data  are  avail- 
able upon  which  to  base  a  decision  as  to  the  best  time  for  appl^ang 
fertilizers  of  different  kinds  in  the  orchard.  Without  doubt  many  factors 
have  a  bearing  in  this  connection.  Among  the  more  important  may  be 
mentioned:  the  varying  states  or  conditions  of  the  plant  as  the  season 
advances,  the  changing  nutrient  value  of  the  soil,  moisture  supply  includ- 
ing the  possibihty  of  losses  from  leaching  and  bacterial  activities  of  differ- 
ent kinds.  It  is  only  as  these  are  understood  and  properly  evaluated  in 
each  individual  case  that  fertilizer  applications  can  be  timed  to  best 
advantage.  When  easily  soluble  nitrogenous  fertilizers  are  required 
large  amounts  should  not  be  put  on  in  the  fall,  during  the  winter  or  too 
early  in  the  spring,  on  account  of  the  danger  of  leaching.  Indeed,  this 
is  always  a  prime  consideration  in  making  nitrogen  applications,  though 
relatively  unimportant  with  other  fertilizers.  On  the  other  hand, 
fertilizers  carrying  nitrogen  in  organic  combination  must  be  applied 
sufficiently  early  to  give  disintegration  processes  time  for  making 
the  nitrogen  available  to  the  plants  before  it  is  too  late  for  them  to 
absorb  it. 

Frequent  observation  and  experience  indicate  that  orchard  fruits 
respond  very  quickly  to  easily  soluble  nitrogenous  fertilizers  such  as 
nitrate  of  soda  and  sulphate  of  ammonia,  when  these  are  made  as  growth 
is  starting  in  the  spring  or  later  during  the  growing  season.  Thus 
Ballou^  reports  a  greatly  increased  set  of  fruit  in  weak,  devitalized  apple 
trees  when  nitrate  of  soda  was  applied  just  before  the  opening  of  the 
flowers.  In  this  case  not  more  than  3  weeks  had  elapsed  before  it  was 
clearly  evident  that  the  trees  were  receiving  benefit  from  the  application. 
In  fact  this  immediate  effect  of  quickly  available  nitrogen  has  led  to  the 
general  practice  of  applying  it  just  as  growth  is  starting  and  it  would 
seem  that  experience  bears  out  the  wisdom  of  so  timing  nitrate  appli- 
cations. On  the  other  hand,  when  nitrogen  is  needed,  not  so  much  for 
aiding  the  setting  of  fruit  or  perhaps  for  increasing  the  vegetative  growth 
made  during  the  early  part  of  the  current  season — this  latter  being  an 
influence  which,  as  yet,  has  not  been  very  accurately  determined — but 
rather  for  its  effects  the  following  season,  through  organic  products 
elaborated  during  the  summer  and  fall  months  and  stored  through  the 
winter,  the  best  time  for  fertilizer  apphcations  may  be  quite  different. 

Some  evidence  in  support  of  this  last  suggestion  is  furnished  by  experi- 
mental work  in  England. ^^  Apphcations  of  quickly  available  fertihzers 
to  orchard  trees  of  a  number  of  varieties  in  August,  supplemented  by 
applications  in  the  spring  at  the  time  of  fruit  setting,  caused  trees  to  bear 
annual  crops.  The  immediate  effect  of  the  midsunnner  applications  is 
to  cause  the  trees  to  hold  their  foliage  later  in  the  fall,  thus  accumulating 


228  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

larger  stores  of  elaborated  foods  and  making  possible  the  formation  of 
stronger,  if  not  more,  fruit  buds. 

The  Relation  of  Seasonal  Conditions  to  Response  from  Fertilizers.— 
Many  features  of  environment  may  be  limiting  factors  to  growth.  The 
supply  of  nutrients  in  the  soil  constitutes  only  one  series  or  group  of 
these  factors.  With  a  change  in  other  factors  it  is  to  be  expected  that  a 
definite  balance  of  nutrients  in  the  soil  will  limit  growth  in  different  ways 
and  a  corresponding  variation  is  to  be  expected  from  the  use  of  a  par- 
ticular fertilizer  on  a  particular  soil  and  for  a  particular  crop,  depending 
on  temperature,  humidity,  rainfall  and  other  factors.  Such  differences 
have  been  studied  in  certain  grain  and  forage  crops.  Thus  applications 
of  nitrogenous  fertilizers  to  grass  land  give  much  more  striking  results 
when  the  season  is  comparatively  dry  than  when  it  is  wet.^^^  Little 
is  known  regarding  the  responses  of  fruit  trees  to  the  same  fertilizer  with 
varying  seasonal  conditions.  The  great  differences  found  in  field  crops, 
however,  suggest  that  some  variations  may  be  expected. 

Summary. — Potash,  phosphoric  acid  and  lime-carrying  fertilizers 
are  seldom  required  by  orchard  trees,  which  rarely  show  a  direct  response 
to  their  application.  However,  these  fertilizers  often  increase  greatly 
the  growth  of  intercrops  or  cover  crops  and  when  these  are  used  for  mulch- 
ing or  green  manuring  purposes  tree  growth  and  production  are  indirectly 
increased.  This  indirect  influence  is  particularly  important  in  case  the 
intercrop  is  a  legume.  Nitrate  of  soda,  sulphate  of  ammonia  and  dried 
blood  have  proved  the  best  of  any  of  the  nitrogenous  fertilizers  tried; 
the  first  two  are  in  most  common  use.  Sodium  nitrate  tends  to  leave  the 
soil  more  basic  in  reaction  and  sulphate  of  ammonia  has  the  opposite 
effect.  These  different  residual  effects  may  be  of  considerable  importance 
under  some  conditions.  Phosphorus  is  generally  applied  as  acid  phos- 
phate ;  potassium,  either  as  muriate  or  sulphate.  Data  as  to  the  best  time 
for  fertilizer  applications  are  meager.  They  indicate,  however,  that  for 
increasing  the  setting  of  fruit,  quickly  available  nitrogenous  fertilizers 
should  be  used  just  as  the  trees  are  starting  growth  in  the  spring.  The 
nature  and  relative  magnitude  of  the  response  from  similar  fertilizer 
applications  may  be  expected  to  vary  considerably  with  different  growing 
season  conditions. 

Suggested  Collateral  Readings 

Ewert,  A.  J.  On  Bitter-Pit  and  the  Sensitivity  of  Apples  to  Poisons.  Proc.  Roy. 
Soc.    Victoria.     24(N.S.):  367-419.     1912. 

Kraus,  E.  J.,  and  Kraybill,  H.  R.  Vegetation  and  Reproduction  with  Special  Refer- 
ence to  the  Tomato.     Ore.  Agr.  Exp.  Sta.  Bui.  149.     1918. 

Gourley,  J.  H.  Studies  in  Fruit  Bud  Formation.  N.  H.  Agr.  Exp.  Sta.  Tech.  Bui.  9. 
1915. 

Wiggans,  C.  C.  Factors  Favoring  and  Opposing  Fruitfulness  in  the  Apple.  Mo. 
Agr.  Exp.  Sta.  Res.  Bui.  31.     1918. 


NUTRITION  229 

Hooker,  H.  D.,  Jr.     Seasonal  Changes  in  the  Chemical  Composition  of  Apple  Spurs. 

Mo.  Agr.  Exp.  Sta.  Res.  Bui.  40.     1920. 
Hedrick,  U.  P.     Twenty  Years  of  Fertilizers  in  an  Apple  Orchard.     N.  Y.  Agr.  Exp. 

Sta.  Bui.  460.     1920. 
Roberts,  R.  H,     Off-year  Apple  Bearing.     Wis.  Agr.  Exp.  Sta.  Bui.  317.     1920. 
Bedford,   H.  A.  R.,  and  Pickering,  S.  U.     The  Effect  of  Grass  on  Trees,  etc.     Pp. 

259-312.     Science  and  Fruit  Growing.     London,  1919. 
Jorgensen,    I.,    and    Stiles,    W.     Carbon    Assimilation.     New    Phytologist    Reprint 

No.  10.     London,  1917. 
Palladin,  V.  I.     Plant  Physiology,  Edit,  by  B.  E.  Livingston.     Chapters  3,  4,  5,  7,  8. 

Pp.  60-117  and  139-212.     Phila.,  1918. 
Russell,  E.  J.     Soil  Conditions  and  Plant  Growth,  Chapters  2,  6,  7.     Pp.  19-51  and 

117-152.     London,  1915. 

Literature  Cited 

1.  Albert,  P.     Forst.  naturwiss.  Ztschr.     3:9.     1894. 

2.  Alderman,  W.  H.     W.  Va.  Agr.  Exp.  Sta.  Bui.  150.     1919. 

3.  Alderman,  W.  H.     Proc.  Am.  Soc.  Hort.  Sci.     17:261-266.     1920. 

4.  Ames,  J.  W.     Ohio  Agr.  Exp.  Sta.  Mo.  Bui.  5.     1920 

5.  Andre,  G.     Compt.  rend.     734:1514.     1903. 

6.  Andre,  G.     Chimie  Agricole.     1:415.     Paris,  1914. 

7.  Ibid.     1:425. 

8.  Ball,  E.  D.,  Titus,  E.  G.,  and  Greaves,  J.  E.     Jour.  Ec.  Entom.     3:187-197. 

1910. 

9.  Ballon,  F.  H.     Ohio  Agr.  Exp.  Sta.  Bui.  301.     1916. 

10.  Bayer,  A.     Pflanzenphysiologische  Bedeutung  der  Cupfer.     Konigsberg,  1902. 

11.  Beamee-Nieuland,  N.     Boschbouwk.  Tydschr.  Tectona.     ll(3):187-205.     1918. 

Cited  in  Exp.  Sta.  Rec.     43:320.     1920. 

12.  Behrens,  J.     Gartenflora.     47:269.     1898. 

13.  Bioletti,  F.  T.     Cal.  Agr.  Exp.  Sta.  Bui.  241  (no  date). 

14.  Black,  C.  A.     N.  H.  Agr.  Exp.  Sta.  Tech.  Bui.  10.     1916. 

15.  Blackmann,  F.  F.     Ann.  Bot.      19:281-295.     1905. 

16.  Bouyoucos,  G.  J.     Mich.  Agr.  Exp.  Sta.  Tech.  Bui.  44.     1919. 

17.  Bradford,  F.  C.     Ore.  Agr.  Exp.  Sta.  Bui.  129.     1915. 

18.  Breazeale,  J.  F.     Jour.  Agr.  Res.     18:272.     1919. 

19.  Brenchley,   W.   E.     Inorganic   Plant  Poisons   and   Stimulants.     Cambr.    Agr. 

Monogs.     Cambridge,  1914. 

20.  Brown,  G.  G.     Ore.  Agr.  Exp.  Sta.  Bui.  159.     1919. 

21.  Brown,  H.  T.,   and  Escombe,  F.     Phil.  Trans.  Roy.  Soc.  London.     190B:233- 

291.     1900. 

22.  Brown,  H.  T.,  and  Escombe,  F.     Proc.  Roy.  Soc.    London.    76B:29-111.     1905. 

23.  Butler,  0.  R.,  Smith,  T.  O.,  Curry,  B.  E.     N.  H.  Agr.  Exp.  Sta.  Tech.  Bui.  13. 

1917. 

24.  Cameron,  F.  K.,  and  Bell,  J.  M.     U.S.D.A.,Bur.  Soils  Bui.  30.     1905. 

25.  Chandler,  W.  H.     Mo.  Ag.  Ex-p.  Sta.  Bui.  113.     1913. 

26.  Chandler,  W.  H.     Mo.  Agr.  Exp.  Sta.  Res.  Bui.  14.     1914. 

27.  Chandler,  W.  H.     Proc.  Am.  Soc.  Hort.  Sci.     17:201-204.     1920. 

28.  Chauzit,  J.     Compt.  rend.  Acad.  Agr.  France.     5:83.5-837.     1919.     Cited  in 

Exp.  Sta.  Rec.     42:222.     1920. 

29.  Colby,  G.  E.     Cal.  Dept.  Agr.  Mo.  Bui.     10:35.     1921. 

30.  Collison,  R.  C.     N.  Y.  Agr.  Exp.  Sta.  Bui.  447.     1920. 

31.  Collison,  S.  E.     Fla.  Agr.  Exp.  Sta.  Bui.  154.     1919. 


230  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

32.  Coupin,  H.     Compt.  rend.     127:400.     1898. 

33.  Coupin,  H.     Compt.  rend.     170:753-754.     1920. 

34.  Coville,  F.  V.     U.S.D.A.,  Bur.  PI.  Ind.  Bui.  193.     1910. 

35.  Coville,  F.  V.     U.S.D.A.  Bui.  6.     1913. 

36.  Cummings,  M.  B.,  and  Jones,  C.  H.     Vt.  Agr.  Exp.  Sta.  Bui.  211.     1919. 

37.  Curtis,  O.  F.     Am.  Jour.  Bot.     7:101-124.     1920. 

38.  Czapek,  F.     Biochemie  der  Pflanzen.     2:156-158.     Jena,  1905. 

39.  Ibid.     2:188. 

40.  Ibid.     2:198. 

41.  Ibid.     2:737. 

42.  Ibid.     2:739. 

43.  Ibid.     2:740. 

44.  Ibid.     2:744. 

45.  Ibid.     2:745. 

46.  Ibid.     2:762. 

47.  Ibid.     2:764,  765. 

48.  Ibid.     2:765. 

49.  Ibid.     2:766. 

50.  Ibid.     2:769. 

51.  Ibid.     2:772. 

52.  Ibid.     2:776. 

53.  Ibid.     2:791. 

54.  Ibid.     2:795. 

55.  Ibid.     2:797. 

56.  Ibid.     2:798. 

57.  Ibid.     2:800. 

58.  Ibid.     2:805. 

59.  Ibid.     2:830. 

60.  Ibid.     2:868. 

61.  Daniel,  L.     Rev.  hort.     10(N.S.):102.     1910. 

62.  Davis,  W.  A.,  Daish,  A.  J.,  and  Sawyer,  G.  C.     Jour.  Agric.  Soc.     6:406-412. 

1914. 

63.  Drinkard,  A.  W.     Va.  Agr.  Exp.  Sta.  Ann.  Kept.     P.  159.     1909-1910. 

64.  Emmons,  E.     Agriculture  of  New  York,  Vol.  1.     Albany,  1849. 

65.  Ewert,  A.  J.     Proc.  Roy.  Soc.  Victoria.     24(N.S.):367-419.     1912. 

66.  Floyd,  B.  F.     Fla.  Agr.  Exp.  Sta.  Ann.  Rept.     Pp.  35R-46R.     1917. 

67.  Ibid.     Bui.  140.     1917. 

68.  Franklin,  J.  H.     Mass.  Agr.  Exp.  Sta.  Bui.  168.     1916. 

69.  Fred,  E.  B.     Va.  Agr.  Exp.  Sta.  Ann.  Rept.     Pp.  132-134.     1908. 

70.  Ibid.     Pp.  138-142. 

71.  Garner,  W.  W.,  and  Allard,  H.  A.     Jour.  Agr.  Res.     18:553-606.     1920. 

72.  Gile,  P.  L.,  and  Carrero,  J.  O.     Porto  Rico  Agr.  Exp.  Sta.  Rept.     Pp.  10-20. 

1917. 

73.  Gile,  P.  L.,  and  Carrero,  J.  O.     Jour.  Agr.  Res.     20:33-62.     1920. 

74.  Gladwin,  F.  E.     N.  Y.  Agr.  Exp.  Sta.  Bui.  458.     1919. 

75.  Goff,  E.  S.     Wis.  Agr.  Exp.  Sta.  Ann.  Rept.     16:289.     1899. 

76.  Ibid.     17:266.     1900. 

77.  Ibid.     18:304.     1901. 

78.  Gonehalli,  V.  H.     Bombay  Dept.  Agr.  Bui.  29.     1914.     (Cited  by  Tottingham, 

W.  E.     Jour.  Am.  Soc.  Agron.     2:6.     1919.) 

79.  Gourley,  J.  H.     N.  H.  Agr.  Exp.  Sta.  Bui.  168.     1914. 

80.  Ibid.     Bui.  190.     1919. 


NUTRITION  231 

81.  Gourley,  J.  H.,  and  Shunk,  V.  D.     N.  H.  Agr.  Exp.  Sta.  Tech.  Bui.  11.     1916. 

82.  Graves,  J.  E.,  Carter,  E.  G.  and  Goldthorpe,  H.  C.     Jour.  Agr.  Res.     16:107- 
135.     1919. 

83.  Gray,  J.,  and  Pierce,  G.  J.     Am.  Jour.  Bot.     6:131-155.     1919. 

84.  Haberlandt,    G.     Bot.    Ztg.     1877.     (Cited    by    Albert,    P.     Forst.  naturwiss. 

Ztschr.     3:9.     1894.) 

85.  Harris,  J.  E.     Mich.  Agr.  Exp.  Sta.  Tech.  Bui.  19.     1914. 

86.  Hart,  E.  B.,  and  Tottingham,  W.  E.     Jour.  Agr.  Res.     5:223-250.     1915. 

87.  Hartwell,  B.  L.     R.  I.  Agr.  Exp.  Sta.  Bui.  183.     1920. 

88.  Hartwell,  B.  L.,  and  Damon,  S.  C.     R.  I.  Agr.  Exp.  Sta.  Bui.  177.     1919. 

89.  Hartwell,  B.  L.,  Pember,  F.  R.,  and  Merkle,  G.  E.     R.  I.  Agr.  Exp.  Sta.  Bui. 

176.     1919. 

90.  Harvey,  E.  M.,  and  Murneek,  A.  E.     Ore.  Agr.  Exp.  Sta.  Bui.  176.     1921. 

91.  Hawaii  Agr.  Exp.  Sta.  Rept.     P.  44.     1919. 

92.  Headden,  W.  P.     Col.  Agr.  Exp.  Sta.  Bui.  131.     1908. 

93.  Ibid.     Bui.  160.     1910. 

94.  Hedrick,  U.  P.     N.  Y.  Agr.  Exp.  Sta.  Bui.  289.     1907. 

95.  Ibid.     Bui.  339.     1911. 

96.  Hedrick,  U.  P.,  and  Anthony,  R.  D.     N.  Y.  Agr.  Exp.  Sta.  Bui.  460.     1919. 

97.  Henrici,  M.     Verhandl.  Naturf.  Ges.  Basel.     30:43-136.     1919. 

98.  Hodgsoll,  H.  E.  P.     Jour.  Pomol.     1:217-223.     1920. 

99.  Hooker,  H.  D.,  Jr.     Science.     46(N.S.):197-204.     1917. 

100.  Hooker,  H.  D.,  Jr.     Mo.  Agr.  Exp.  Sta.  Res.  Bui.  40.     1920. 

101.  Hopkins,  C.  G.,  and  Aumer,  J.  P.     III.  Agr.  Exp.  Sta.  Bui.  182.     1915. 

102.  Horticulturist.     1:60.     1846. 

103.  Jorgensen,  I.,  and  Stiles,  W.     Carbon  Assimilation.     New  Phytologist  Reprint 

No.  10.     London,  1917. 

104.  Jost,  L.     Pflanzenphysiologie.     3te  Auflage.     P.  103.     Jena,  1913. 

105.  Kearney,  T.  H.     U.S.D.A.,  Bur.  PL  Ind.  Bui.  125.     1908. 

106.  Kelley,  W.  P.     Hawaii  Agr.  Exp.  Sta.  Bui.  26.     1912. 

107.  Kelley,  W.  P.,  and  Thomas,  E.  E.     Cal.  Agr.  Exp.  Sta.  Bui.  318.     1920. 

108.  Kiesselbach,  T.  A.     Nebr.  Agr.  Exp.  Sta.  Res.  Bui.  6.     1916. 

109.  Kirby,  R.  S.     la.  Acad.  Sci.     25:265.     1918. 

110.  Klebs,  G.     Abh.  Naturf.  Ges.  Halle.     25:116.     1906. 

111.  Klebs,  G.     Proc.  Roy.  Soc.     London.     82:547-558.     1910. 

112.  Korstian,  C.  F.,  Hartley,  C,  Watts,  L.  F.,  and  Hahn,  G.  G.     Jour.  Agr.  Res. 

21:153-169.     1921. 

113.  Kraus,  E.  J.     Bienn.  Crop  Pest  and  Hort.  Rept.  Ore.  Agr.  Exp.  Sta.     1:71-78. 

1911-12. 

114.  Kraus,  E.  J.     Ore.  Agr.  Exp.  Sta.  Research  Bui.  1.     Pt.  1.     1913. 

115.  Kraus,  E.  J.,  and  Kraybill,  H.  R.     Ore.  Agr.  Exp.  Sta.  Bui.  149.     1918. 

116.  Laurent,  E.     Compt.  rend.  Soc.  roy.  bot.  Belg.     29(2):71-76.     1890. 

117.  Laurent,  E.     Bui.  Acad.  roy.  Belg.     (3)  32:815-865.     1896. 

118.  Lawes,  J.  B.,  and  Gilbert,  J.  H.     Rothamstead  Memoirs.     2:291-292.     1880. 

119.  Ibid.     2:390-405. 

120.  Lawes,   J.   B.,   Gilbert,   J.   H.,   and  Masters,    M.  T.     Rothamstead    Memoirs. 

2:1252-1263.     1882. 

121.  Leclerc,  J.  A.,  and  Breazeale,  J.  F.     U.S.D.A.  Yearbook.     Pp.  389-402.     1908. 

122.  Leclerc    du    Sablon.     Rev.    gen.  Bot.     16:341-368;  386-401.     1904.     18:5-25; 

82-96.     1906. 

123.  Lewis,  C.  I.,  and  Allen,  R.  W.     Hood  River  Branch  (Ore.)  Agr.  Exp.  Sta.  Rept. 

1914-1915. 


232  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

124.  Loew,  O.,  and  May,  D.  W.     U.S.D.A.,  Bur.  PL  Ind.  Bui.  1.     1901. 

125.  Loughridge,  R.  H.     Cal.  Agr.  Exp.  Sta.  Bui.  133.     1901. 

126.  Lubimenko,    V.    N.     Mem.    Acad.    Sci.    Petrograd.    8:33.     1916.     (Cited    in 

Physiol.  Abstr.     4:413-414.     1919.) 

127.  Magness,  J.  R.     In  Ore.  Agr.  Exp.  Sta.  Bui.  139.     1916. 

128.  Ibid.  Bui.  146.     1917. 

129.  Maquenne,  L.,  and  Demoussey,  E.     Bui.  Soc.  Chem.     27:266-278.     1920. 

130.  McCool,  M.  M.,  and  Millar,  C.  E.     Mich.  Agr.  Exp.  Sta.  Tech.  Bui.  43.     1918. 

131.  McCue,  C.  A.     Trans.  Peninsular  Hort.  Soc.     1915. 

132.  McMurran,  S.  M.     U.S.D.A.  Bui.  756.     1919. 

133.  Mer,    E.     Bui.    Soc.    Bot.     45:299.     1898.     d'Arbaumont,    J.     Ann.    Sci.  nat. 

Bot.     (8)13:319-423;  14:125-212.     1901. 

134.  Michel  Durant,  E.     Variation  des  substances  hydrocarbonees  dans  les  feuilles. 

Dissertation.     Nemours.     1917. 

135.  Molisch,  H.     Bot.  Ztg.     55:49-61.     1897. 

136.  Montemartini,  L.     Atti.  Inst.  Bot.  Univ.  Pavia.     (2)15:1-42.     1918. 

137.  Munson,  W.  M.     Me.  Agr.  Exp.  Sta.  Bui.  89.     1903. 

138.  Neubauer,  C.     Ann.  Oenol.     5:343-364.     1875. 

139.  N.  Mex.  Agr.  Exp.  Sta.  Ann.  Rept.     P.  31.     1912-13. 

140.  N.  Y.  Agr.  Exp.  Sta.  Ann.  Rep.     Pp.  166-168.     1891. 

141.  Nobbe,    F.,   Baeseler,   D.,   and  Will,   H.     Landw.   Versuchs-Sta.     30:381-423. 

1884. 

142.  Oddo,  B.,  and  Polacci,  G.     Gazz.  chim.  ital.     50(l):54-70. 

143.  Paddock,  W.,  and  Whipple,  O.  B.     Fruit  Growing  in  Arid  Regions.     P.  330. 

New  York,  1911. 

144.  Palladin,  V.  I.     Plant  Physiology.     Edit,  by  B.  E.  Livingston.     P.  82.     Phila., 

1918. 

145.  Ibid.     P.  83. 

146.  Ibid.     P.  254. 

147.  Partridge,  N.  L.     Proc.  Am.  Soc.  Hort.  Sci.     16:104-109.     1919. 

148.  Petit,  P.     Comp.  rend.     111:975.     1893:  Ascoli,  Lieb.  Physiol.  Chem.     28:426. 

1899. 

149.  Pfeiffer,  O.     Ann.  Oenol.     5:271-315.     1875. 

150.  Pickering,  S.  U.     Ann.  Bot.     31:183-187.     1917. 

151.  Quaintance,  A.L.     Ga.  Agr.  Exp.  Sta.  Ann.  Rept.     13:350.     1900. 

152.  Rassiguier.     Prog.  Agr.  et  Vit.     18(No.  35):204-206.     1892.     (Cited  by  Gile, 

P.  L.,  and  Carrero,  J.  O.     Jour.  Agr.  Res.     20:38.     1920.) 

153.  Reimer,  F.  C.     Ore.  Agr.  Exp.  Sta.  Bui.  163.     1919. 

154.  Reimer,  F.  C.     Ore.  Agr.  Exp.  Sta.  Bui.  166.     1920. 

155.  Richter,  L.     Landw.  Versuchs-Sta.     73:457-477.     1910. 

156.  Rivera,  V.     I    problemi  agrari    del  mezzogiorno.   Mem.  R.  Staz.  Ratal.  Veg. 

P.  18.     Rome,  1919. 

157.  Roberts,  I.  P.     Cornell  Univ.  Agr.  Exp.  Sta.  Bui.  103.     1895. 

158.  Roberts,  R.  H.     Proc.  Am.  Soc.  Hort.  Sci.     14:105.     1917. 

159.  Roberts,  R.  H.     Wis.  Agr.  Exp.  Sta.  Bui.  317.     1920. 

160.  Schreiner,  O.,  and  Shorey,  E.  C.     U.S.D.A.,  Bur.  Soils  Bui.  74.     1910. 

161.  Schreiner,  O.,  and  Skinner,  J.  J.     U.S.D.A.,  Bur.  Soils  Bui.  70.     1910. 

162.  Ibid.     Bui.  77.     1911. 

163.  Ibid.     Bill.  87.     1912. 

164.  Ibid.     Bui.  108.     1914. 

165.  Schreiner,  O.,  Reed,  H.  S.,  and  Skinner,  J.  J.     U.S.D.A.,  Bur.  Soils  Bui.  47. 

1907. 


NUTRITION  233 

166.  Shedd,  O.  M.     Ken.  Agr.  Sta.  Bui.  188.     1914. 

167.  Shibata,  K.,  Shibata,  Y.,  and  Kasiwagi,  I.     Jour.  Am.  Chem.  Soc.     41:208. 

1919. 

168.  ShuU,  C.  A.     Science.     52(N.S.):376-378.     1920. 

169.  Skinner,  J.  J.     U.S.D.A.,  Bur.  Soils  Bui.  83.     1911. 

170.  Sorauer,  P.     Pflanzenkrankheiten.     3te.  Auflage.     1 :289.     Berlin,  1909. 

171.  Ibid.     1:292. 


172. 

Ibid.     1:297. 

173. 

Ibid.      1:305. 

174. 

Ibid.     1:310. 

175. 

Ibid.     1:312. 

176. 

Ibid.     1:391. 

177. 

Spoehr,  H.  A. 

178. 

Stewart,  J.  P. 

Carnegie  Inst.  Wash.  Publ.  287.     1919. 
Pa.  Agr.  Exp.  Sta.  Bui.  153.     1918. 

179.  Stewart,  R.     111.  Agr.  Exp.  Sta.  Bui.  227.     1920. 

180.  Stewart,  R.     111.  Agr.  Exp.  Sta.  Circ.  245.     1920. 

181.  Stoykowitch,    W.     Recherches    phj'siologiques    sur    la    prune.     Dissertation. 

Nancy,  1910. 

182.  Taylor,  R.  H.     Cal.  Agr.  Exp.  Sta.  Bui.  297.     1918. 

183.  Taylor,  T.  C,  and  Nelson,  J.  M.     Jour.  Am.  Chem.  Soc.     42:1726-1738.     1920. 

184.  Teodoresco,  E.  C.     Ann.  Sci.  nat.  Bot.     (8)  10:141-164.     1899. 

185.  Thompson,  R.  C.     Ark.  Agr.  Exp.  Sta.  Bui.  123.     1916. 

186.  Tottingham,  W.  E.     Jour.  Am.  Soc.  Agron.     2:1.     1919. 

187.  Trabut,  W.     Cited  by  Kearney,  T.  H.     U.S.D.A.,  Bur.  PL  Ind.  Bui.  125.     1908. 

188.  Tr^iog,  E.     Wis.  Agr.  Exp.  Sta.  Res.  Bui.  41.     1916. 

189.  Tsuji,  T.     La  Planter.     60:413-414.     1918. 

190.  Van  Slyke,  L.  L.,  Taylor,  O.  M.,  and  Andrews,  W.  H.     N.  Y.  Agr.  Exp.  Sta. 

Bui.  265.     1905. 

191.  Vasnievski,  S.     Bui.  intern,  acad.  sci.  Cracovie  B.     Pp.  615-686.     1917. 

192.  Voechting,  H.,  Jahrb.  wiss.  Bot.     25:149-208.     1893. 

193.  Walster,  H.  L.     Bot.  Gaz.     69:97-125.     1920. 

194.  Warren,  F.  G.     N.  J.  Agr.  Exp.  Sta.  Rept.     P.  199.     1906. 

195.  Webber,  H.  J.,     U.S.D.A.  Yearbook.     P.  193.     1894. 

196.  Weber,  R.    Landw.  Versuchs-Sta.     18:18-48.     1875. 

197.  Weber,  R.     Forst.  naturwiss.  Ztschr.     1:13.     1893. 

198.  Westgate,  J.  M.      Hawaii  Agr.  Exp.  Sta.  Press  Bui.  51.     1916. 

199.  Wheeler,  H.  J.     U.S.D.A.  Farmers  Bui.  77.     1905. 

200.  Wheeler,  H.  J.      Manures  and  Fertilizers.     Pp.  113-124.     New  York,  1914. 

201.  Whiting,  A.  L.,  and  Schoonover.,  W.  R.     111.  Agr.  Exp.  Sta.  Bui.  225.     1920. 

202.  Whitten,  J.  C,  and  Wiggans,  C.  C.     Mo.  Agr.  Sta.  Buls.  131,  141,  147.     1915- 

1917. 

203.  Wickson,  E.  J.     California  Fruits.     P.  164.     San  Francisco.     1910. 

204.  Wiegand,  K.  M.     Bot.  Gaz.     41:373.     1906. 

205.  Wiesner,  J.     Die  Entstehung  des  Chlorophylls.     Vienna,  1877. 

206.  Woodbury,  C.  G.,  Noyes,  N.  A.  and  Oskamp,  J.     Ind.  Agr.  Exp.  Sta.  Bui. 

207.     1917. 

207.  Wright,  W.  J.     Proc.  Am.  Soc.  Hort.  Sci.     11:9-14.     1912. 

208.  Zaliesski,    W.     Die    Bedingungen    der    Eiweissbildimg   den    Pflanzen.     P.    53 

Charkow.     1900. 

209.  Zimmerman,  A.     Ztsch.  angew.  Chem.     6:426.     1893. 


SECTION  III 

TEMPERATURE  RELATIONS  OF 
FRUIT  PLANTS 

Of  the  four  great  factors  of  plant  environment,  moisture,  soil,  light 
and  temperature,  the  fruit  grower  can  modify  two  considerably.  He 
can  irrigate  or  drain,  he  can  fertilize,  if  necessary;  he  can,  to  some  extent, 
modify  soil  texture;  light  and  temperature  he  must  take  as  they  come. 
The  object  of  the  present  section  is  to  indicate  how,  though  temperatures 
cannot  be  changed,  except  in  certain  minor  respects,  fruit  growing  can  be 
modified  to  capitalize  favorable  temperatures  or  to  minimize  the  unfav- 
orable effects.  Knowing  the  various  effects  of  heat  or  its  lack  the  grower 
is  able  to  chose  fruits  best  adapted  to  existing  conditions,  to  avoid 
attempting  the  impossible  or  the  very  hazardous,  to  pick  favorable 
sites  and  so  to  manipulate  his  plants  that  they  will  have  the  best  possible 
adjustment  to  the  various  temperature  conditions  of  their  environment. 

Temperatures  influence  plants  in  several  ways  bearing  directly  on 
fruit  growing:  (1)  they  delimit  zones  beyond  which  the  growing  of  specific 
fruits  becomes  commercially  hazardous  because  of  low  winter  tempera- 
tures; (2)  they  delimit  zones  beyond  which  the  growth  of  certain  fruits 
becomes  unprofitable  because  of  high  summer  temperatures;  (3)  they 
make  certain  areas  unprofitable  for  some  fruits  because  of  low  summer 
temperatures;  (4)  they  render  much  good  land  of  doubtful  value  for 
several  fruits  because  of  danger  from  spring  frosts;  (5)  within  areas  ordi- 
narily safe  for  growing  certain  specific  fruits  an  occasional  deviation 
from  normal  may  cause  considerable  damage;  (6)  some  insects  and 
diseases  are  more  or  less  dependent  on  proper  temperatures  for  their 
optimum    development. 

Lest  this  statement  should  give  an  unpleasant  connotation  to  tem- 
perature relations,  it  should  be  stated  conversely  that  these  very  limita- 
tions predicate  the  presence  at  some  places  of  temperatures  favorable 
to  fruit  growing.  The  existence  of  fruit  growing  at  all  is  obvious  proof. 
Unfortunately  attention  is  centered  rather  on  the  Umitations,  so  that, 
though  many  unfavorable  conditions  are  fairly  closely  understood, 
optimum  temperatures  for  the  various  fruits  are  not  defined  so  clearly. 

Schimper,^^*  commenting  on  the  difficulty  of  temperature  investigations, 
states:  the  "existence  of  such  action  on  vegetable  organisms  is  less  clearly 
recognizable  than  is  that  of  water.  We  can  directly  observe  the  ingress  of  water 
into  a  plant  and  its  egress,  we  can  explain  physiologically  the  effects  caused  by 

234 


TEMPERATURE  RELATIONS  OF  FRUIT  PLANTS  235 

these,  and  we  can  follow  the  transpiration  current  along  its  course,  whereas  the 
action  of  heat  is  carried  on  in  the  molecular  region  of  the  protoplasm  beyond 
our  ken,  and  is  visible  to  us  only  in  its  final  consequences,  such  as  the  acceleration, 
retardation  or  complete  cessation  of  physiological  processes.  The  cecological 
phenomena  display  similar  processes.  Protective  adaptations  against  a  want 
or  superfluity  of  water  are  within  our  power  of  observation,  those  against  cold 
and  heat  are  entirely  beyond  them.  We  can  directly  see  whether  any  plant 
naturally  inhabits  a  dry  or  a  moist  station,  but  not  whether  it  belongs  to  the 
flora  of  a  cold  or  warm  climate.  Indeed  plants  from  hot  deserts  frequently  have 
a  strong  resemblance  in  habit  to  those  of  polar  zones." 

The  metabolism  of  a  plant  may  be  regarded  as  a  complicated  set  of 
chemical  reactions,  subject  to  several  influences.  Among  the  factors 
governing  chemical  reactions  and  vital  processes  the  chemist  and  the 
physiologist  recognize  temperature.  There  are  certain  limits,  apparently, 
for  all  vital  reactions,  limits  wide  in  some  instances,  narrow  in  others. 
Some  plants  require  a  relatively  high  temperature  for  setting  in  motion 
the  processes  known  as  growth;  others  will  carry  on  similar  processes 
at  a  lower  point.  One  may  go  on  at  a  certain  temperature  in  a  given 
plant,  while  another  in  the  same  plant  may  require  more  heat.  At  a 
low  temperature  a  plant  is  said  to  rest;  certain  processes  are  in  truth 
suspended,  but  others  are  inaugurated.  Finally,  there  is  a  point  so 
low  that  the  plant  cannot  exist;  it  dies  apparently  from  cold.  On  the 
other  hand,  all  plants  show  their  maximum  growth  activity  within  the 
limits  of  a  comparatively  small  range  of  temperature;  above  these 
limits  some  reactions  are  retarded  or  some  are  so  accelerated  as  to 
become  harmful,  or  new  injurious  reactions  begin  and  the  net  results  that 
are  recognized  as  growth  or  fruitfulness  are  diminished;  here  again  the 
point  is  finally  reached  where  the  equilibrium  of  reactions  is  broken  and 
death  ensues. 

Withal,  it  must  be  considered  that  temperature  is  only  one  of  the 
factors  affecting  plant  growth.  Even  a  single  plant  may  be  limited  at 
various  times  by  quite  different  features  of  its  environment. 

Investigation  has  shown  that  in  soy  beans  in  Maryland  growth  was  controlled 
during  one  fortnight  by  temperature,  but  in  the  next  by  the  rainfall-evaporation 
ratio.  1-^  In  Ceylon  it  has  been  found  that  with  ^^awe  and  FwrcrtEa  temperature 
is  always  the  limiting  factor;  with  Dendrocalamus  sometimes  it  is  temperature, 
sometimes  water  supply.  In  January  Vitis  is  Umited  in  growth  by  temperature 
and  in  July  by  the  water  supply,  while  with  Capparis  and  Stiff  tea  the  Umiting 
factors  are  water  supply  during  the  day  and  temperature  during  the  night.  ^^^ 

MacDougaP^^  shows  the  operation  of  limiting  factors  in  his  study  of  the 
growth  of  tomato  fruits.  As  the  temperature  of  the  fruits  increased,  growth 
progressed  until  the  rise  caused  a  loss  of  water  exceeding  the  gain.  The  higher 
temperatures  did  not  accelerate  growth  unless  the  relative  humidity  of  the  atmos- 
phere was  high;  a  rise  in  temperature  with  decreased  humidity  retarded  or  stopped 
growth  or  even  caused  an  actual  diminution  of  volume. 


CHAPTER  XIV 

GROWING  SEASON  TEMPERATURES 

Horticulturists,  particularly  in  the  Old  World,  have  recognized  in 
a  manner  the  importance  of  growing  season  temperatures  to  fruit  plants. 
Most  of  the  efforts  at  precise  study  of  this  nature,  however,  have  been 
made  by  those  particularly  interested  in  phenology. 

HEAT  UNITS 

Various  investigators  have  made  efforts  to  show  that,  wherever 
a  given  plant  is  grown,  to  complete  its  cycle  that  plant  requires  a  certain 
amount  of  heat.  When  it  has  received  this  amount  of  heat,  whether 
in  n  days  or  n  +  r  or  n  -\-  s  days,  it  will  have  completed  its  cycle.  The 
outline  of  this  idea  was  enunciated  first,  probably,  in  1735  by  Reaumur. ^ 
Numerous  writers  since  that  time  have  attempted  to  refine  the  methods 
used  in  studies  of  this  sort.  Adanson,  for  example,  recognizing  that 
averages  which  included  readings  below  freezing  were  misleading,  inas- 
much as  such  temperatures  do  not  reverse  plant  activity  but  merely 
suspend  it,  discarded  all  such  readings.  Others  have  assumed  higher 
temperatures  as  the  zero  points  for  their  calculations.  Gasparin  con- 
sidered that  "effective  temperatures"  began  at  5°C.  He  also  considered 
a  thermometer  in  full  sunshine  on  sod  to  show  the  true  temperature  of 
the  plant  more  nearly  than  one  registering  air  temperature  alone  and 
that  "the  warmth  in  the  sunshine  is  to  the  warmth  of  the  air  in  the  shade 
as  though  one  has  been  transported  in  latitude  from  3  to  6°  farther 
south. "^  DeCandolle^^  believed  sunlight  in  itself  to  influence  vital 
processes  independently  of  temperature,  since  several  annuals  which 
he  had  under  observation  required  a  greater  total  of  heat  degrees  for 
flowering  and  for  ripening  in  the  shade  than  they  received  in  full  sunlight. 

The  Relative  Values  of  Different  Efifective  Temperatures.— Most 
investigations  in  phenology  until  comparatively  recent  date  have  been 
based  on  the  assumption  that,  above  the  basic  temperature  which 
initiates  plant  growth,  each  degree  is  of  equal  value  with  any  other. 
Lately,  however,  the  principle  of  Van't  Hoff  and  Arrhenius,  namely, 
"that  within  limits,  the  velocity  of  most  chemical  reactions  doubles  or 
somewhat  more  than  doubles  for  each  rise  in  temperature  of  10°C.," 
has  been  shown  to  have  considerable  bearing  on  certain  processes  in 
plants.  As  the  Livingstons^*'^  point  out,  certain  of  the  purely  physical 
processes  involved  in  growth  do  not  follow  this  principle  and  its  applica- 

236 


GROWING  SEASON  TEMPERATURES 


237 


tion  to  plants  Is,  therefore,  qualified.  Fully  recognizing  the  numerous 
limitations  inherent  in  the  data  at  present  available,  they  have,  never- 
theless, tentatively  assigned  "efficiency  indices"  to  the  various  degrees  of 
temperature,  reproduced  in  part  in  Table  1,  and  applied  them  to  the 
temperature  data  at  various  points  in  the  United  States. 

In  a  subsequent  paper  Livingston  proposes  a  different  system,  based 
on  Lehenbauer's  studies  of  root  growth  in  maize. ^°^ 

This  system  differs  from  the  others  in  that  it  is  based  on  observed  rates  of 
growth  and  in  taking  cognizance  of  a  decreased  rate  of  growth  with  temperatures 
above  the  optimum.  A  comparison  of  the  values  obtained  with  the  three 
systems  is  given  in  Table  1.  Livingston  evidently  regards  this  work  only  as  a 
step  toward  further  study,  since  he  states:  "...  these  indices  are  to  be  re- 
garded as  only  a  first  approximation  and  .  .  .  much  more  physiological  study 
will  be  required  before  they  may  be  taken  as  generally  applicable.  In  the  first 
place,  they  are  based  upon  tests  of  only  a  single  plant  species,  maize,  and  there  are 


Table  1. — A  Comparison  of  Temperature  Index  Values,  Starting  with  40°F. 
AS  Unit,  According  to  Three  Systems 


System 

Temperature 

Remainder 

Exponential 

Physiological 

40 

1 

1 . 0000 

1.000 

50 

11 

1.4696 

6.333 

58 

19 

2.0000 

16.111 

68 

29 

2.9391 

46.000 

76 

37 

4.0000 

82.333 

86 

47 

5.8782 

120.000 

94 

55 

8.0000 

103.333 

99 

60 

9.6980 

73.111 

112 

7.3 

16 . 0000 

3.778 

probably  other  plants  ...  for  which  they  are  not  even  approximately  true. 
...  no  doubt  other  phases  of  growth  in  the  same  plant  may  exhibit  other 
relations  between  temperature  and  the  rate  of  shoot  elongation.  Third,  these 
indices  refer  to  rates  of  shoot  elongation,  and  there  are  many  other  processes 
involved  in  plant  growth,  which  may  require  other  indices  for  their  proper  inter- 
pretation in  terms  of  temperature  efficiency.  Fourth,  they  apply  strictly  only 
under  the  moisture,  Hght  and  chemical  conditions  that  prevailed  in  Lehenbauer's 
experiments  .  .  .  Fifth,  and  finally,  plants  in  nature  are  never  subject  to 
any  temperature  maintained  for  any  considerable  period  of  time.    .    .    ." 

Influence  of  Latitude  on  Heat  Requirements. — Phenological  data 
on  any  single  fruit  plant  gathered  over  a  wide  area  are  rather  scarce  at 
present  and  those  available  are  not  altogether  satisfactory.  However,  in 
combination  with  temperature  data  compiled  by  the  Weather  Bureau 


238 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


some  of  these  data  are  interesting,  particularly  since,  to  some  extent, 
they  corroborate  findings  of  other  investigators. 

In  the  Early  Harvest  Apple. — Table  2  is  compiled  from  phenological 
data  gathered  by  Bailey^  and  from  daily  normal  temperatures  for  the 
various  points, ^^  except  that  the  temperature  for  Columbia,  Mo.,  is 
joined  with  the  phenological  data  for  Boonville,  a  short  distance  away. 
Some  of  the  phenological  data  may  be  open  to  question,  as,  for  example, 
the  ripening  date  for  Thomasville,  Ga.,  but  even  with  some  allowance  for 
errors,  there  is  apparent  a  general  tendency  for  temperature  summations 
at  southern  points  to  exceed  those  of  more  northern  location.     Though 

Table  2. — Heat  Units  Calculated  on  Several  Systems  Compared  with  Dates 
OF  Blossoming  and  of  Ripening  in  the  Early  Harvest  Apple 


Date 

Normal 
temperature 
at   average 
date  of  blos- 
soming, 
Fahrenheit 

Remainder 

Expo- 
nential 
Jan.  1  to 
ripening 

Physio- 
logical 
Jan.  1  to 
ripening 

Locality 

Jan.    1 
to  blos- 
soming 

Blos- 
som to 
ripening 

Total 
Jan.    1 
to  ripen- 
ing 

Blos- 
soming 

Ripen- 
ing 

Thomasville,  Ga.... 

Augusta,  Ga 

Atlanta,  Ga 

Raleigh,  N.  C 

Boonville,  Mo 

Erie,  Pa 

Ithaca,  N.  Y 

Rochester,  N.  Y . . . 

Mar.  10 
Mar.  27 
Apr.  8 
Apr.  6 
Apr.  20 
May  23 
May  10 
May  21 

July  10 
May  30 
July  1 
July  2 
June  23 
Aug.  18 
July  28 
Aug.  11 

59 
59 
59 
56 
56 
60 
55 
59 

933 
922 

819 
597 
347 

558 
283 
470 

3,952 
1,820 
2,573 
2,560 
1,729 
2,600 
2,102 
2,267 

4,945 
2,742 
3,392 
3,157 
2,076 
3,158 
2,385 
2,743 

536 
315 
378 
366 
234 
341 
261 
293 

8,383 
3,455 
5,005 
4,758 
2,979 
2,110 
3,305 
1,547 

relative  positions -of  certain  stations  change  with  different  systems  of 
computing  the  effective  temperatures,  the  same  tendency  holds  through- 
out and  is  perhaps  most  evident  with  the  physiological  index  summations. 
If  a  different  zero  point — say  50°F. — be  assumed,  the  relative  differences 
are  not  reduced  materially;  in  fact  they  are  rather  intensified,  for  though 
northern  points  would  have  somewhat  lower  summation  totals,  those  for 
Thomasville,  Ga.,  would  not  be  reduced  at  all,  since  the  normal  daily 
temperature  for  early  January  is  50°F. 

In  the  Elberta  Peach. — Gould"  reports  ripening  dates  for  the  Elberta 
peach  at  various  points  in  the  United  States.  Certain  of  these  seem  near 
enough  to  stations  for  which  Bigelow^^  has  computed  daily  normal  tem- 
peratures to  make  comparisons  valid.  Table  3  shows  summations  to  the 
date  of  ripening  and  for  the  year  at  these  points,  with  the  proportion 
which  they  bear  respectively  to  each  other,  Linsser^'^^  has  suggested 
that  this  ratio  should  be  constant,  but  the  data  here  presented  do  not 
support  his  suggestion.  The  same  tendency  to  greater  summations  in 
the  south  than  in  the  north  is  apparent  here.  Waugh^''^  found  heat  units 
for  the  blossoming  of  the  "American  Wild  Plum"  in  1898  as  follows: 


GROWING  SEASON  TEMPERATURES 


239 


Stillwater,  Okla.,  967;  Parry,  N.  J.,  909;  State  College,  Pa.,  725;  Burling- 
ton, Vt.,  577. 


Table  3. 


-Heat  Units  to  the  Date  of  Ripening  of  Elberta  Peach  at  Various 
Points  and  Total  Heat  Units  for  the  Year 


Date  of 
ripening 

Remainder 

Linsser's 
constant 

Expo- 

Locality 

To 
ripening 

For  year 

index  to 
ripening 

Atmore,  Ala 

Plain  Dealing,  La 

Van  Buren,  Ark 

Vacaville,  Cal 

Manteo,  N.  C 

Central  Ind 

Lewiston,  Idaho 

Palisades,  Col 

Port  Clinton,  Ohio 

Freewater,  Ore 

Lake  region,  Mich 

Ipswich,  Mass 

July    11 
July    10 
July    15 
July     6 
Aug.   10 
Sept.  15 
Aug.     1 
Aug.  26 
Aug.  25 
Aug.   17 
Sept.  10 
Sept.  17 

4,654 
4,572 
3,817 
3,332 
4,911 
4,090 
3,006 
4,483 
3,639 
3,622 
3,483 
3,880 

9,540 
8,143 
8,006 
7,478 
8,475 
5,346 
5,260 
6,001 
5,170 
5,488 
4,292 
4,669 

48.8 
56.1 
47.7 
44.6 
57.9 
76.5 
.57.1 
74.7 
70.4 
66.2 
81.1 
83.1 

522.9 
519.2 
432.6 

562.6 
499.4 
334.2 
500.0 
392.8 
403.4 
374.1 
418.2 

In  Chestnut  Blight. — Stevens  has  made  an  interesting  application  of  these 
various  constants  to  studies  of  the  growth  of  tlie  chestnut  blight  fungus.  Assum- 
ing 45°F.  as  the  lowest  effective  temperature,  he  compares  the  summations  of 
temperatures  above  that  point  at  various  localities  with  the  observed  growth  of 
the  blight  cankers  and  finds  that  "the  temperature  summation  falls  off  somewhat 
more  rapidly  northward  than  does  the  amount  of  growth."  In  a  later  paper  he 
reports  that  the  summations  on  the  "Physiological  basis"  do  not  fit  the  observed 
growth  so  well  as  the  summations  of  remainder  or  exponential  indices.  ^^^'  ^^^ 

Variations  in  Heat  Requirements  from  Season  to  Season. — Sand- 
sten^^^  made  a  study  of  heat  units  accumulating  at  blossom  time  for  the 
apple  and  plum  during  several  seasons  at  Madison,  Wis.  As  appears  from 
Table  4,  composed  of  items  taken  from  his  data,  he  found  considerable 
variation  from  year  to  year  and  from  variety  to  variety.     Combining 

Table  4. — Number  of  Positive  Temperature  Units  (above  32°F.)   Receh^ed 
Each  Year  from  Jan.   1  to  the  Date  of  Fir.st  Bloom 


Variety 

1902 

1903 

1904 

1905 

Wealthv 

810.5 
837.0 
837.0 
785.0 
785.0 

837.5 
810.5 
928.0 
837.5 
810.5 

752.0 
727.0 
752.5 
707.0 
752.5 

690  0 

Borovinka 

599  0 

Charlamoff 

713  0 

Hibernal 

599  0 

Grimes. 

652  0 

240 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


with  these  figures  the  total  heat  units  for  the  last  6  months  of  the  pre- 
vious growing  season  he  secured  a  closer  approach  to  uniformity  as  ex- 
pressed in  percentage  of  the  smallest  yearly  total  to  the  greatest  yearly 
totals  for  any  variety  (see  Table  5).  Sandsten  interprets  his  data  as 
showing  that  other  factors  besides  the  heat  units  from  Jan.  1  have  a 


Table 


-Number  of  Positive  Temperature    Units   (above  32°F.)    Received 
From  Preceding  July  1  to  Date  of  First  Bloom 


Variety 


1901-1902 


1902-1903 


1903-1904    1904-1905 


Wealthy . . . 
Borovinka . 
Charlamoff 
Hibernal .  .  . 
Grimes.  .  .  . 


5,106.5 
5,133.5 
5,133.5 
5,081.5 
5,081 . 5 


4,827.5 
4,801.5 
4,918.5 
4,827.5 
4,801.0 


4,601.5 
4,576.0 
4,601.5 
4,556.0 
4,601.5 


48,01.5 
47,10.5 
48,24.5 
47,10.5 
47,63.5 


bearing  on  the  time  of  flowering  and  enumerates  as  possible  factors  the 
stage  of  advancement  of  the  buds  at  the  time  of  growth  cessation  in  the 
fall,  the  size  of  the  crop  borne  in  the  previous  year,  "soil  conditions  and 
the  amount  of  plant  food  present  in  the  soil;  and  fifth,  the  individual 
characteristics  and  state  of  health  of  the  tree  or  plant."  General  observa- 
tion on  peach  trees  shows  a  sequence  in  opening  blossoms  corresponding 
to  the  stage  of  advancement  of  these  buds  in  the  fall,  the  difference  in 
time  of  flowering  on  the  same  branch  amounting  sometimes  to  several 
days,  which  would  make  a  difference  occasionally  of  50  units  or  more  on 
the  Fahrenheit  scale.  Magness  makes  an  interesting  suggestion  in  this 
connection  which  is  referred  to  under  Fruit  Bud  Formation. 

Seeleyi^"  applied  the  method  of  temperature  summations  to  the  Late 
Crawford  peach,  as  recorded  in  the  Mikesell  data  for  Wauseon,  Ohio. 
His  summary  of  results,  shown  in  Table  6,  indicates  no  close  agreement 
from  year  to  year  for  the  same  locality.  Somewhat  closer  tallying  was 
secured  when  maximum  figures  were  used  (line  4) .  Seeley  shows  that  air 
temperatures  as  recorded  by  thermometers  in  the  conventional  shelter  do 
not  indicate  at  all  closely  the  actual  temperatures  of  the  leaves. 

Table  6. — The  Least  and  the  Greatest  Temperature  Summations  in  the  Life 
Phase  of  the  Late  Crawford  Peach 

{After  Seeleij''^) 


Summation 

Jan.   1  to 
blossoming 

Blossoming 
to  ripening 

Jan.  1  to 
ripening 

Ripening  to 
blossoming 

Average 

Least 

183 

362 

50 

64 

2,776 

3,991 

70 

71 

3,030 

4,347 

70 

72 

486 

1,250 
38 
61 

Greatest 

Percentage 

Maximum  (per  cent.) 

61 

69 

GROWING  SEASON  TEMPERATURES  241 

Acclimatization  to  Varying  Amounts  of  Heat. — It  is  conceivable  that 
through  acclimatization  plants  graduallj^  may  require  more  or  less  heat 
for  a  given  function;  evidence  to  this  effect  is  cited  by  Bailey.^  Cuttings 
of  Concord  grape  from  Maine,  central  New  York  and  southern  Louisiana 
planted  simultaneously  under  uniform  conditions  at  Ithaca,  N.  Y.,  made 
in  a  given  time  the  following  respective  growths:  2.66  inches,  1.6  inches 
and  1.3  inches.  The  seed  potato  trade  of  ]\Iaine  is  founded  on  the  quick- 
ened response  to  a  given  temperature  by  potatoes  grown  there.  Data 
already  cited  in  this  chapter  show  a  tendency  for  plants  in  northern 
sections  to  attain  a  given  stage  of  development  with  less  heat  than  in 
southern  sections.  Elsewhere  it  is  shown  that  plants  accommodate  them- 
selves to  a  wide  range  of  moisture,  nutrient  and  light  conditions;  there- 
fore it  is  not  surprising  that  they  show  a  corresponding  adaptation  to 
various  temperature  conditions. 

In  General. — It  is  possible  that  more  detailed  measurements,  taken 
perhaps  on  a  different  basis  than  that  used  by  climatologists,  would 
secure  more  uniformity  than  the  figures  cited  above.  Temperatures 
taken  in  sunlight  would  seem  to  be  more  reliable  expressions  of  conditions 
in  buds  and  leaves  than  those  taken  in  shade.  Some  writers  have  sug- 
gested maximum  temperatures  as  the  basis  for  calculations.  In  any  case, 
however,  it  seems  doubtful  if  temperature  alone  can  be  made  the  index 
of  plant  activities. 

Schimper^"^  aptly  points  out  that  "different  organs  and  functions  require 
very  different  amounts  of  heat,  that  unfavorable  temperatures  cause  subsequent 
inhibition,  and  that  other  factors  besides  heat,  especially  humidity,  cooperate 
and  intervene.  We  need  not,  then,  be  surprised  if  there  is  very  Uttle  accord  in 
phaenological  observations,  and  that  the  utmost  one  can  do  is  to  admit  their 
having  a  certain  importance  for  purely  descriptive  geographical  botany  in  the 
characterization  of  certain  districts.  No  importance,  on  the  other  hand,  need 
be  assigned  to  the  theoretical  views,  nor  to  the  sum  total  of  temperatures." 

OPTIMUM  TEMPERATURES 

It  is  well  known  that  some  plants  grow  at  lower  temperatures  than 
others.  The  necessity  of  a  certain  amount  of  heat  during  the  growing 
season  is  recognized  in  the  statement  that  in  some  regions  the  summers  are 
too  cool  for  certain  fruits. 

Variation  within  the  Species  or  Variety.— In  considerable  areas  of 
north  central  Europe,  peach  growing  is  limited,  not  by  the  cold  of  winter 
but  by  the  low  summer  temperature.  The  same  limitation,  though 
less  obvious,  probably  applies  to  pears,  as  is  indicated  by  the  transition 
from  open  exposures  in  the  south  of  France  to  the  trained  and  sheltered 
trees  in  the  north.  Among  plants  of  warmer  climates  the  date  palm 
shows  a  heat  requirement  that  is  not  satisfied  in  all  sections  where  the 


242  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

winters  are  sufficiently  mild.  The  grape  is  among  the  plants  most 
frequently  cited  by  phenological  workers  as  showing  this  same  exaction 
in  its  requirement.  Variety  adaptation  in  apples  probably  depends  on 
growing  season  temperature,  among  other  factors.  In  addition  it  seems 
rather  likely  that  this  factor  is  operative  in  another  way  though  its 
effects  necessarily  are  masked  by  their  own  results;  low  summer  tem- 
perature may  delay  maturity  to  such  an  extent  that  an  ensuing  winter  of 
medium  intensity  is  injurious.  The  obvious  and  immediate  cause  of 
trouble  here  would  be  winter  injury  but  the  antecedent  cause  would  be 
the  cool  summer.  Much  of  the  winter  injury  characteristic  of  parts  of 
Europe  seems  to  be  involved  with  low  summer  temperatures. 

The  effects  of  temperature  alone  in  certain  phases  can  be  compared 
best,  perhaps,  in  plants  of  the  deserts,  since  these  regions  show  rather 
greater  uniformity  in  other  conditions  than  most  humid  sections.  In 
the  date  palm  temperature  assumes  considerable  importance. 

According  to  Swingle i^^^  "The  northern  limit  and  the  limit  of  altitude  in 
northwestern  Africa  at  which  dates  can  be  grown  are  set  more  by  the  deficient 
summer  heat  failing  to  ripen  the  fruit  than  by  the  cold  in  winter."  Very  early 
ripening  dates,  he  reports,  can  be  grown  far  to  the  north  where  the  summers  are 
not  warm  enough  to  ripen  later  varieties.  Swingle  confirms  DeCandoUe's 
calculation  of  64.4°F.  as  the  point  below  which  no  effect  is  produced  on  flowering 
or  fruiting  of  the  date  palm.  Affirming  that  under  desert  conditions  temperature 
summations  have  considerable  significance  he  states  that  2000°C.,  using  18°C. 
as  the  zero  point,  are  necessary  to  ripen  Deglet  Noor  dates  satisfactorily. 

Mason^23  cites  Caruso  as  authority  for  the  statement  that  51°  to  52°F. 
is  zero  point  for  the  olive  and  adds  that  in  California  zero  may  be  some- 
what higher,  probably  55°  to  56°F.  He  assigns  a  definite  number  of  heat 
units  as  necessary  for  ripening  the  olive  before  autumn,  but  points  out 
that  in  some  localities  with  low  summer  temperatures  and  little  or  no 
frost  in  winter  the  fruit  may  remain  longer  on  the  trees.  In  some 
places  the  requisite  number  of  heat  units  is  not  accumulated  until 
December. 

The  apple  shows  some  indications  of  the  effects  of  excessive  summer 
heat  at  some  points  in  the  United  States  and  of  deficient  summer  heat  at 
others.  Along  the  southern  limits  of  its  successful  culture  there  is  a 
general  tendency  to  vigorous  vegetative  growth  with  httle  fruit  produc- 
tion and  much  of  the  fruit  that  is  borne  rots  on  the  tree.  In  that  period 
when  apple  varieties  were  being  tested  and  when  the  varietal  composition 
of  the  orchard  was  not  determined  by  market  standards  of  the  large 
cities,  the  Ribston  Pippin  attained  a  much  greater  popularity  in  eastern 
Maine  than  in  any  other  section  of  the  country  then  growing  apples. 
Other  Enghsh  varieties  were  more  favorably  received  there  than  in  any 
other  state.     Downing^^  considered  that  the  Ribston  attained  far  better 


GROWING  SEASON  TEMPERATURES  243 

quality  along  the  Penobscot  River  than  in  the  middle  states.  Inci- 
dentally he  mentioned  English  gooseberries  as  succeeding  better  around 
Bangor,  Maine,  than  elsewhere.  It  seems  probable  that  the  cool  sum- 
mers of  that  section  favored  the  best  development  of  these  fruits. 

The  converse  limitation  is  less  generally  understood  but  it  is  none  the 
less  potent.  Most  varieties  of  apple  have  certain  heat  requirements  for 
the  attainment  of  their  best  quality  or  indeed  for  their  ripening.  Cions 
of  the  Baldwin,  favored  by  a  succession  of  mild  winters  in  Aroostook 
County,  bore  fruit  which  failed  to  ripen  because  it  was  arrested  in  its 
development  by  cold  weather  while  still  green.^^  Shaw^'^  found  marked 
differences  in  Ben  Davis  grown  in  various  sections,  indicating  incomplete 
development  in  much  of  the  northern  apple  growing  section.  The  limits 
of  successful  culture  of  many  varieties  are  conditioned  by  the  minimum 
winter  temperatures,  thus  rather  obscuring  the  importance  of  suminer 
heat  but,  as  with  other  fruits,  there  seems  to  be  some  reason  for  consider- 
ing winter  hardiness  in  some  cases  to  be  affected  by  summer  temperatures. 
So  far  as  climatological  data  show,  the  minimum  winter  and  average 
winter  temperatures  for  Boston,  Mass.,  and  Columbia,  Mo.,  are  almost 
identical,  but  their  summer  temperatures  differ  considerably.  Winesap  is 
considered  tender  and  unsatisfactory  in  Massachusetts  while  in  Missouri 
it  is  one  of  the  best  commercial  varieties.  Apparently  the  limitation  is 
set  by  winter  temperature  in  the  Mississippi  valley  and  by  summer 
temperature,  directly  or  indirectly,  along  the  Atlantic  seaboard.  The 
northern  commercial  limit  of  York  Imperial  crosses  the  Mississippi  near 
the  southern  Iowa  border  and  the  Atlantic  coast  in  New  Jersey.  ^^^  Here 
again  the  correspondence  between  the  northern  limits  east  and  west  is 
better  in  summer  temperatures  than  in  those  of  winter.  The  same  con- 
trol is  evident  with  Rome  Beauty. 

Shaw^^^  concluded  after  extended  study  that  a  certain  optimum 
summer  temperature  may  be  assigned  to  each  variety  of  apple,  ranging 
from  52°F.  for  Hibernal  and  Oldenburg  to  67°F.  for  Terry  and  Yates. 
As  appears  from  Table  7  the  temperature  range  of  the  chief  commercial 
varieties  is  somewhat  more  narrow.  A  considerable  effect,  however,  on 
the  limits  of  commercial  cultivation  of  apple  varieties  must  be  assigned 
to  summer  temperature. 

Table  7. — Optimum  Average  Summer  Temperatures  for  Leading  Commercial 

Varieties 
{After  S/iaw)'") 

Baldwin 56°F.  Yellow  Newtown 60°F. 

Rhode  Island 56  York  Imperial 62 

Northern  Spy 56  Grimes 62 

Wealthy 56  Stayman 63 

Jonathan 59  Winesap 64 

Delicious 59  Ben  Davis 64 


244  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

In  the  United  States,  Lippincotti°"  traced  isotherms  for  combined  June,  July, 
August  and  September  temperatures  and  correlated  them  with  the  grapes  growing 
in  the  zones  thus  marked  out.  Here  a  combined  selection  is  exercised  by  summer 
and  by  winter  temperatures  and  in  addition,  as  pointed  out  elsewhere  the  summer 
temperatures  doubtless  have  some  influence  on  the  effect  of  winter  cold.  How- 
ever, there  can  be  no  doubt  that  summer  temperatures  have  a  direct  effect  of 
their  own.  In  favored  localities  in  the  zone  with  a  mean  of  65°F.  he  found 
Chnton  and  Delaware,  with  a  few  other  varieties.  In  the  67°F.  zone  he  included 
Concord  and  Hartford  Prolific;  Isabella,  Diana  and  Rogers'  Hybrids  he  con- 
sidered to  require  70°F.  Catawba,  Norton's  Virginia,  Herbemont  and  Scupper- 
nong  were  assigned  to  regions  with  average  summer  temperatures  of  72°  or  higher. 

Differences  within  the  Variety  for  Separate  Processes. — Different 
processes  in  the  same  plant  have  different  optimum  temperatures. 

Phytolacca  decandra  at  Carmel,  Cal.,  grows  well  but  flowers  only  under  certain 
conditions  as,  for  example,  when  prostrate  branches  receive  sufficient  additional 
heat  from  the  soil  to  enable  them  to  form  viable  seeds,  while  the  erect  stems 
do  not.^"  In  connection  with  fruit  setting  it  is  shown  that  lower  temperatures 
than  usual  convert  male  blossoms  of  the  papaya  into  perfect  flowers.  Schimper 
points  out  the  difference  in  the  temperature  curve  for  the  two  forms  of  gaseous 
exhange  and  states  that  assimilation  occurs  at  lower  temperatures  than  any 
other  function.  He  cites  evidence  of  assimilation  in  Abies  excelsa  and  other 
plants  at  —  40°C.  and  cites  Bohm  as  finding  the  optimum  for  the  walnut  at  30°C. 
No  distinct  respiration  could  be  observed  in  Abies  below  —  10°C.;  this  function 
increases,  speaking  in  general  terms,  with  the  temperature  until  the  lethal  point  is 
approached.  Quoting  Schimper"^  again:  "There  are,  however,  certain  physio- 
logical processes  for  which  not  only  the  optima,  but  also  the  upper  zeros  are  so 
low  that,  as  a  rule,  they  can  take  place  only  in  winter,  late  autumn,  or  early 
spring.  The  category  of  functions  that  are  active  at  low  temperatures  only 
includes  among  others  the  obscure  processes  which  are  fermentative  in  nature, 
according  to  Sachs'  hypothesis,  and  which  awaken  into  activity  hibernating 
parts  of  plants ;  among  such  processes  may  be  cited  the  conversion  of  starch  into 
fatty  acids  and  the  reverse.  .  .  .  Lower  temperatures  exert  a  favourable  influ- 
ence on  the  sexual  organs  and  on  the  parts  oecologically  connected  with  them 
(perianths,  inflorescence  axes)  in  many  parts  of  the  temperate  and  frigid  zones. 
The  cardinal  degrees  for  the  growth — and  perhaps  for  the  inception — of  the 
primordia  of  flowers  are  often  much  lower  than  for  the  growth  of  vegetative 
shoots,  so  that  the  former  are  favoured  by  a  relatively  lower  temperature,  and  the 
latter  by  a  high  temperature,  during  development.  It  is  well  known  that 
Crociis,  Hyacinthus,  and  other  perennial  herbs  do  not  send  out  flowers  or  inflores- 
cences at  a  high  temperature,  but  shoot  out  luxuriantly  into  leaf.  Also  in  the 
forcing  of  fruit  trees  the  temperature  must  be  kept  moderate  before,  and  espe- 
cially during,  the  blossoming  period.  For  the  same  reason  many  temperate 
plants  seldom  blossom  in  the  tropics;  for  example,  most  of  our  fruit  trees.  .  .  . 
Kurz  found  in  the  mountains  of  Burmah  that  increased  coolness  due  to  increased 
altitude  expedited  the  blossoming  of  temperate  plants  such  as  Rhododendron  and 
Gentiana,  but  delayed  that  of  tropical  ones." 


GROWING  SEASON  TEMPERATURES 


245 


As  Schimpei-i^i  points  out,  the  forcing  of  fruit  under  glass  is  merely  a 
shortening  of  the  dormant  season  and  the  period  of  maturity  is  advanced 
only  as  much  as  the  inception  of  growth  precedes  that  in  the  open.  The 
temperatures  found  best  for  the  trees  indoors  are  those  they  receive  at 
corresponding  stages  out  of  doors  in  favorable  regions;  higher  temperatures 
are  not  beneficial. 

Price  1^^  reports  investigations  showing  certain  temperatures  more 
favorable  to  the  opening  of  fruit  buds  than  others.  With  branches  of 
various  fruit  trees  in  incubators  maintained  at  different  temperatures  he 
found  progressive  acceleration  in  the  opening  of  the  buds  with  the  higher 
temperatures.     Some  of  the  data  he  reports  are  used  in  compiling  Table  8. 

Table  S. — Influence  of  Temperature  on  Opening  of  Fruit  Buds 


Fruit 


Date  of 
beginning 


Davs  to  full  bloom 


70°F. 


79°F. 


88°F. 


Abundance  plum. . . 

Hale  plum 

Luster  peach 

Kieff er  pear 

Oldenburg  apple 

Rome  Beauty  apple 


Jan.  28,  1908 
Dec.  3,  1909 
Feb.  2,  1909 
Mar.  7,  1910 
Apr.  1,  1909 
Apr.  22,  1909 


Tufts''^  reports  interesting  indications  that  very  high  temperatures  may 
retard  the  ripening  of  fruit.  "Here,"  he  states,  referring  to  the  Winters  section 
in  the  Sacramento  valley,  "...  the  apricot  ripens  some  two  or  three  weeks  prior 
to  the  ripening  of  the  apricot  crop  in  the  Santa  Clara  Valley,  although  apricot 
trees  in  the  Santa  Clara  Valley  bloom  ten  days  earUer  than  they  do  in  the  Winters 
section.  Undoubtedly  the  nearness  of  the  ocean  and  the  influence  of  the  San 
Francisco  Bay  profoundly  modify  the  climate  of  the  Santa  Clara  Valley.  The 
Apricot  crop  in  the  Winters  section  is  entirely  harvested  by  July  1. 

"When  it  comes  time  for  the  prune  harvest,  however,  we  find  that  the  Santa 
Clara  Valley  is  generally  pretty  well  along — about  half  way  through — before  the 
prunes  in  the  Sacramento  Valley  are  ready.  The  only  explanation  we  have  for 
this  apparent  inconsistency  is  the  fact  that  probably  the  temperatures  for  the 
ripening  of  the  apricot  crop  are  optimum  in  the  Winters  section.  However,  after 
the  first  of  July  the  weather  gets  excessively  warm,  with  the  result  that  the  prunes 
are  retarded  in  their  development,  and  the  optimum  temperatures  for  the  develop- 
ment of  the  prune  crop  probably  exist  in  the  Santa  Clara  Valley  during  the  latter 
part  of  the  growing  season." 

Schimper/^"  emphasizing  that  different  functions  require  different 
temperatures,  states:  "the  oecological  optimum  temperature  does  not 
remain  constant  during  the  whole  development  of  a  plant,  at  least  in  tem- 


246 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


perate  regions,  but  .  .  .  shows  a  rise  as  development  proceeds.  .  .  .  We 
learn  too  from  the  art  of  fruit  forcing  that  we  must  regard  the  rise  not  as 
constant  but  as  oscillating."  He  cites  Pynaert  in  giving  the  tempera- 
tures shown  in  Table  9  as  most  favorable  in  forcing  the  peach.  At  two 
periods  the  temperature  is  lowered.  Ward  ^^i  in  England  and  Schneider^^^ 
in  northwest  Europe  differ  somewhat  in  detail  from  this  temperature 
statement;  Schneider  indicates  a  lowering  of  temperature  at  the  time  of 
stoning. 

Table  9. — Optimum  Temperatures  in  Forcing  the  PeachI'" 
(Degrees  Centigrade) 


Day  temperature 


Night  temperature 


First  week 

Second  week 

Third  week 

To  flowering .... 

At  flowering 

After  flowering . . 
During  stoning . . 
After  stoning.  .  . 
At  fruit  ripening 


9  to  10 
10  to  12 
12  to  15 
15  to  18 

8  to  12 

15  to  18 
12  to  15 

16  to  19 
20  to  22 


5  to  7 
7  to  9 
9  to  11 

11  to  14 

6  to  10 

11  to  14 
9  to  11 

12  to  15 
15  to  17 


Variation  in  Quality  with  Amount  of  Summer  Heat. — The  fruit 
which  has  received  the  most  careful  study  in  its  relation  to  temperature 
conditions  is  the  grape.  Blodgettj^"  writing  in  1857,  when  grape  growing 
in  America  was  in  an  experimental  stage,  predicted  very  closely,  from 
climatological  data,  the  geographic  distribution  of  the  industry  in  the 
United  States. 

Boussingault^^  early  remarked  on  the  variation  in  yield  and  quality  of  wine 
of  a  vineyard  in  Flanders,  the  variation  depending  on  the  temperature  of  the 
growing  season,  and  reported  data  shown  in  Table  10.  Baragiola,'^  taking  succes- 
sive samples  of  grapes  through  two  autumns,  found  a  striking  correspondence 
between  sugar  increase  and  temperature,  regardless  of  the  stage  of  ripening  at 
which  the  low  or  high  temperatures  occurred.  A  brief  period  of  warm  weather 
late  in  the  season  compensates  apparently  to  a  considerable  degree  for  earher 
deficiencies :  a  brief  period  of  cool  weather  at  the  same  stage  apparently  goes  far 
to  nullify  previous  favorable  conditions.  Heat  requirements  for  grapes  during 
the  growing  season  can  be  understood  best  from  European  experience  since  the 
climatology  of  this  fruit  has  been  studied  most  extensively  there  and  is  to  a 
considerable  degree  free  from  the  compUcation  of  winter  temperature  limitations. 
Boussingault22  considered  that  the  mean  temperature  of  the  growing  season 
must  be  at  least  59°F.  and  of  the  summer  65°  to  67°F.  to  produce  Vinifera  grapes 
satisfactorily.  In  some  of  the  equatorial  table  lands  of  South  America,  he 
states,  where  the  mean  temperature  is  62°  to  66°F.  with  little  range,  though  the 


GROWING  SEASON  TEMPERATURES 


247 


Table  10. — Relation  of  Summer  Temperatures  to  Yield  and  Character  of 

Wine-- 


M 

ean  temperature 

Wine,   per 
acre  (gallons) 

Percentage 
of   alcohol 

Year 

Growing 
season,  de- 
grees Centi- 
grade 

Summer, 

degrees 

Centigrade 

Beginning 
of  autumn, 

degrees 
Centigrade 

Alcohol  per 
acre  (gallons) 

1833 

14.7 

17.3 

11.4 

311 

5.0 

11.4 

1834 

17.3 

20.3 

17.0 

314 

11.2 

46.3 

1835 

15.8 

19.5 

12.3 

621 

8.1 

50.0 

1836 

15.8 

21.5 

12.2 

544 

7.1 

38.6 

1837 

15.2 

18.7 

11.9 

184 

7.7 

14.0 

vines  flourish  the  grapes  never  become  thoroughly  ripe  and  good  wine  cannot  be 
made  where  the  constant  temperature  is  not  at  least  68°F.  Besides  a  warm 
summer,  a  mild  autumn  free  from  continued  low  temperature  is  necessary. 
Some  regions  are  assured  of  sufficient  heat  in  every  summer;  others  must  have 
a  summer  warmer  than  the  average  to  produce  a  satisfactory  wine.  Along 
the  doubtful  zone  of  grape  growing  the  careful  selection  of  site  is  emphasized. 

Variation  in  Season  of  Maturity  with  Amount  of  Summer  Heat. — 

The  effect  of  summer  temperatures  on  the  time  of  ripening  and  on  keeping 
quahties  is  well  known.  Thq  Wealthy,  a  fall  or  early  winter  apple  in 
Minnesota,  becomes  a  summer  apple  in  Missouri.  The  Baldwin  loses 
quality  and  becomes  progressively  a  poorer  keeper  toward  the  south 
except  at  higher  and  cooler  altitudes.  Sometimes  the  transition  is  rather 
abrupt.  The  Dudley,  a  winter  apple  in  Aroostook  County,  Maine,  is  a 
fall  apple  at  Bangor  and  a  summer  apple  farther  south. ^^  Apples  grown 
in  southern  latitudes  develop  color  over  a  larger  part  of  the  surface,  but 
the  colors  are  more  intense  in  the  north. 


SOIL  TEMPERATURES 

That  the  temperature  of  the  soil  is  not  without  influence  on  plant 
growth  is  evident  from  the  florist's  resort  to  bottom  heat  for  certain 
plants  and  the  rather  definite  heat  requirements  for  the  rooting  of  cut- 
ings.  It  has  been  shown  that  Opuntia  versicolor  can  be  stimulated  to  con- 
siderable vegetative  growth  despite  unfavorably  cool  atmosphere  by  the 
maintenance  in  the  soil  of  favorable  temperatures  for  root  growth.^" 
Lindley^''*  statedthatacertain  variety  of  A^^e^ww^ntw  though  in  full  vegeta- 
tive vigor  was  without  flowers  when  the  soil  temperature  was  85°F.,  but 
blossomed  at  70  to  75°F.,  while  another  variety  ceased  blossoming  at 
this  same  temperature. 

Obvious  difficulties  are  encountered  in  attempting  a  determination 
of  suitable  temperatures  for  root  growth  in  trees.  Lindley^"^  arranged 
a  statement  of  favorable  soil  temperatures  for  various  fruits,  based  on 


248  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

observations  in  sections  where  these  fruits  flourish;  the  growing  season 
temperatures  thus  indicated  range  from  54°F.  for  the  gooseberry,  59°F. 
for  the  apple,  and  65°F.  for  the  peach  to  85°F.  for  the  mango.  Goff^'' 
found  that  root  growth  begins  very  early  in  most  fruit  plants  in  Wisconsin, 
starting  in  most  cases  in  advance  of  the  buds.  When  currant  buds  were 
but  little  swollen  some  of  the  new  roots  were  3  inches  long.  Goff  stated, 
however,  that  warmer  temperatures  did  not  accelerate  root  growth  as 
much  as  might  be  expected  from  the  early  start.  Comparison  of  the 
growth  of  young  apple  trees  under  various  systems  of  culture,  with  accom- 
panying differences  in  soil  temperature,  has  shown  that  the  two  systems 
inducing  the  greatest  extremes  in  temperature  resulted  in  practically 
the  same  growth. ^^^  xhe  extremes,  however,  were  not  widely  separated. 
It  would  seem  that  in  some  cases  when  a  choice  of  stocks  is  possible 
the  adaptability  of  the  several  stocks  to  soil  temperatures  should  be 
considered,  along  with  other  factors.  It  appears  rather  illogical,  for 
example,  to  plant  prune  trees  on  peach  roots  in  a  soil  so  cold  that  it 
would  not  be  considered  suitable  for  peaches.  An  instance  of  at  least 
partial  adaptability  to  soil  temperatures  has  been  reported  in  Baluchistan, 
where  plums,  peaches,  etc.,  on  Black  Damask  and  Mazzard  roots  repeat- 
edly failed  to  thrive,  though  the  same  combinations  are  satisfactory 
in  Great  Britain. ^^  Using  other  stocks  such  as  Mariana,  Myrobolan 
and  Mahaleb,  that  apparently  are  better  adapted  to  hot,  dry  soils,  much 
better  results  were  secured. 

INDIRECT  TEMPERATURE  EFFECTS 

Finally,  another  limiting  effect  of  growing  season  temperatures  should 
be  considered,  namely,  that  on  fungous  diseases.  Apple  scab,  for  example, 
has  a  generally  northern  range,  suggesting  adaptability  to  cool  summers, 
while  blotch  is  confined  to  sections  with  rather  warm  summers.  Pear 
blight  is  distinctly  a  warm  weather  disease;  brown  rot  is  favored  by 
high  temperatures  in  conjunction  with  humidity.  All  these  diseases  take 
toll  of  the  fruit  grown  where  they  are  present;  brown  rot,  in  conjunction 
with  curculio,  makes  plum  growing  a  hazardous  occupation  in  the  south- 
east United  States  and  blight  practically  prohibits  the  commercial 
production  of  the  European  pear  in  the  southeast  and  in  the  Mississippi 
valley. 

Summary. — Functional  activity  and  growth  of  any  kind  in  a  plant 
have  definite  temperature  requirements.  Within  the  limits  between 
which  the  growth  processes  can  proceed  development  is  slowest  near  each 
extreme — that  is,  close  to  the  lower  and  close  to  the  upper  hmit.  Growth 
is  most  rapid  at  an  optimum  temperature  somewhere  between  the  two 
extremes,  but  usually  nearer  the  upper  than  the  lower  limit.  Further- 
more the  optimum  for  certain  growth  processes  is  quite  different  from 
that  for  others  within  the  same  plant  and  the  extremes  hkewise  may 


GROWING  SEASON  TEMPERATURES  249 

be  different  for  different  activities.  Consequently  it  becomes  extremely 
difficult,  if  not  impossible,  to  assign  definite  values  to  different  temperatures 
in  their  total  growth  effects,  and  the  "heat  units"  necessary  for  com- 
pleting certain  changes,  or  carrying  the  plant  through  certain  aspects 
of  its  seasonal  life  history,  vary  considerabl}^  with  conditions.  In  general 
fewer  heat  units  are  required  by  a  given  plant  in  northern  than  in  southern 
latitudes.  Other  conditions  being  equally  favorable,  there  is  the  best 
varietal  adaptation  in  sections  where  growing  season  temperatures 
most  nearly  approach  the  optimum  for  the  variety  in  question.  The 
importance  of  summer  growing  temperatures  in  determining  the  com- 
mercial limits  of  fruit  varieties  is  underestimated.  Summer  temperature 
likewise  exerts  an  important  influence  in  determining  the  season  of 
maturity  of  the  fruit.  Soil  temperature  is  of  possible  importance  in 
influencing  growth  and  in  determining  the  geographical  range  of  certain 
varieties.  Injurious  effects  of  soil  temperatures  can  be  minimized 
sometimes  by  the  use  of  stocks  of  the  right  kinds.  Summer  tempera- 
tures also  have  an  important  indirect  effect  on  orchard  plants  through 
their  influence  on  the  range  or  activity  of  certain  parasites. 


CHAPTER  XV 

WINTER  KILLING  AND  HARDINESS 

The  limits  to  fruit  growing  set  by  low  winter  temperatures  have  been 
indicated.  This  limitation  has  been  shown  to  be  influenced  more  or 
less  by  other  factors,  precipitation  in  some  cases,  summer  temperatures 
in  others.  Low  winter  temperatures  are  important,  however,  in  other 
respects  than  merely  marking  boundaries  separating  a  section  where 
a  given  fruit  is  grown  from  another  section  where  it  is  not.  Damage 
by  freezing  is  not  confined  to  any  one  region;  it  is  as  definitely  an  injurious 
factor  in  CaUfornia  and  Florida  for  tender  species  as  it  is  in  Montana 
or  Wisconsin  for  the  more  hardy  fruits.  It  is  not  confined  to  the  border- 
lands of  a  fruit  zone  but  in  one  way  or  another  makes  itself  felt  well 
within  the  regions  adapted  to  fruit  growing.  It  is  not  a  simple  matter 
of  uniform,  predictable  reaction  to  a  given  temperature  but  is  modified, 
intensified  or  palliated  by  varying  factors  and  is  itself  probably  a  group 
of  fatal  or  damaging  reactions  assembled  for  convenience  or  for  want 
of  discriminating  classification  under  the  single  name  of  winter  killing. 

DEATH  FROM  FREEZING 

Several  explanations  of  the  actual  process  of  killing  of  tissue  by  low 
temperatures  have  been  made;  it  seems  possible  that  there  may  be  more 
than  one  way  by  which  the  killing  is  brought  about.  Parenthetically, 
it  should  be  stated  that  the  original  theory  and  the  one  still  most  fre- 
quently advanced  by  practical  men,  i.e.,  that  death  by  cold  is  due  to 
expansion  accompanying  freezing  and  a  consequent  rupture  of  the  cell 
walls,  is  not  tenable  as  can  be  proved  mathematically  or  by  microscopic 
examination.  The  bursting  of  trunks  and  limbs,  cited  to  justify  this 
contention,  is  considered  later.  The  view  held  most  generally  by  inves- 
tigators ascribes  death  to  withdrawal  of  water  from  the  cell,  a  process 
comparable  to  death  by  plasmolysis. 

Tissue  Freezing  is  Accompanied  by  Cell  Dehydration. — Numerous 
investigators  have  shown  that  ice  is  very  rarely  formed  within  the  cell 
unless  the  cooling  is  very  rapid,  more  rapid,  in  fact,  than  would  occur  in 
nature.  Before  freezing  begins,  since  the  cell  sap  contains  substances 
in  solution  and  because  of  capillary  supercooling,  most  tissues  must  be  at 
a  temperature  several  degrees  below  the  freezing  point.  The  first  evident 
step  in  the  process  of  freezing  is  a  contraction  of  the  protoplasm  and  the 
appearance  of  water  in  the  intercellular  spaces  where  it  has  been  forced 
or  drawn  from  the  cell.     Ice  formation  begins  at  various  points  in  the 

250 


WINTER  KILLING  AND  HARDINESS  251 

intercellular  spaces,  frequently  making  lens-shaped  masses  of  hexagonal 
crystals,  larger  at  the  side  which  draws  on  the  greater  number  of  cells. 
As  the  growing  ice  needles  deplete  the  water  of  the  intercellular  spaces, 
more  is  drawn  from  the  cell  contents.^^^  The  continuance  of  this  process, 
however,  makes  the  sap  remaining  within  the  cells  more  concentrated 
and  thus  increases  "the  force  with  which  the  remaining  quantities  of 
water  are  held."^^"'  A  still  stronger  force,  operating  as  a  reserve,  is  that 
known  as  molecular  capillarity,  holding  with  extreme  tenacity  a  certain 
amount  of  water  of  imbibition.  Hence,  it  is  with  increasing  difficulty 
that  ice  formation  continues  and  it  must  cease  sooner  or  later  unless  the 
temperature  be  lowered  further.  Moreover,  the  very  process  of  solidi- 
fication liberates  a  certain  amount  of  heat.  Therefore  it  is  not  surprising 
that,  as  the  temperature  falls,  the  ice  formation  for  each  degree  becomes 
progressively  less.  Mliller-Thurgau  found,  at  4.5°C.,  63.8  per  cent,  of 
the  water  of  an  apple  frozen,  while  at  -15.2°C.  only  79.2  per  cent,  had 
frozen. 214  Wiegand-^^  found  very  little  ice  in  dormant  twigs  of  many 
species  of  forest  trees  at  20°F.  At  0°F.  ice  was  plainly  visible  in  buds  of 
19  species  out  of  the  27  examined";  6  of  the  remaining  8  showed  ice, 
but  in  small  scattered  crystals,  at  —  15°F.  These  buds  "all  contained 
little  cell-sap  and  small  cells  with  rather  thick  walls." 

As  the  ice  crystals  increase,  the  cell  walls  collapse  and  become  packed 
together  in  dense  masses.  Buds  and  bark  of  hardy  trees  show  this 
condition,  as  do  evergreen  leaves,  but  at  suitable  temperatures  they 
expand,  draw  back  the  water  and  become  normal. 

Wiegand"^  reports:  "The  ice  was  found  to  occur  always  in  broad  prismatic 
crystals  arranged  perpendicular  to  the  excreting  surface;  and  usually  formed  a 
single  continuous  layer  throughout  the  mesophyll  of  the  scale  or  leaf,  to  accom- 
modate which  the  cells  were  often  separated  to  a  considerable  distance.  This 
ice  sheet  was  composed  of  either  one  or  two  layers  of  the  prismatic  crystals, 
depending  on  the  water  content  of  the  adjacent  surfaces,  and  was  often  as  thick 
as  the  whole  normal  scale.  The  cells  surrounding  the  ice,  having  lost  their  water 
content,  were  in  a  more  or  less  complete  state  of  collapse,  depending  upon  the  re- 
sistance of  the  walls,  and  often  occupied  a  space  smaller  than  the  ice  itself.  These 
cells  were  uninjured,  however,  and  would  resume  their  normal  condition  on 
thawing.  ...  In  young  anthers  the  ice  often  filled  the  entire  anther  cavity 
and  in  it  the  pollen  grains  were  imbedded  in  a  completely  collapsed  state." 
At  temperatures  between  — 23.5°C.  and  —  18°C.  in  the  apple  and  pear  the 
tissue  was  "packed  full  of  ice  in  shoot  and  in  the  mesophyll  of  the  scales."  In 
general,  the  species  in  which  ice  formed  most  readily  had  larger  cells,  a  higher 
water  content  and  a  greater  proportion  of  water  to  cell  wall  and  protoplasm. 

"In  the  twigs,"  Wiegand  states,  "ice  is  also  present  in  very  cold  weather, 
where  it  may  be  found  in  three  different  localities.  The  largest  quantity  occurs 
in  the  cortex,  where  the  ice  crystallizes  in  prisms  arranged  in  single  or  double 
series  according  to  the  law  of  freezing  tissues.  The  ice  is  more  frequently  in 
the  form  of  a  continuous  ring,  or  really  a  cylinder,  extending  entirely  around  the 


252  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

twig,  prying  apart  the  cells  of  the  cortex  in  which  it  lies.  The  outer  cylinder 
of  cortex  in  such  twigs  is  completely  separated  from  the  inner  layers  when  frozen. 
In  a  few  species  instead  of  the  continuous  layer,  lens-shaped  ice  masses  are  inter- 
polated irregularly  throughout  the  cortex.  The  cortical  cells  after  the  withdrawal 
of  water  are  as  completely  collapsed  as  were  those  in  the  bud  scales,  but  they  also 
usually  regain  their  normal  condition  on  thawing.  In  the  wood  ice  rarely  forms 
in  large  quantities.  It  is  usually  confined  to  small  masses  in  the  vessels  them- 
selves, or,  according  to  some  authors,  sometimes  extends  in  radial  plates  in  the 
pith  rays.  In  sectioning  twigs  I,  m.yself,  have  never  seen  ice  in  the  wood  else- 
where than  in  the  vessels  or  wood  cells.  In  the  pith  the  ice,  so  far  as  I  have 
been  able  to  observe,  always  occurs  within  the  cells  and  therefore  in  very  small 
masses."  As  Wiegand  points  out,  Miiller-Thurgau  found  ice  in  the  large  vessels 
and  frequently  in  the  wood  cells  of  pear  and  most  distinctly  in  the  grape. 

Frozen  twigs  of  several  species  were  found  to  expand  on  thawing,  two  apple 
twigs,  for  example,  increasing  in  diameter  from  2.97  milUmeters  and  3.89  milli- 
meters to  3.03  millimeters  and  3.95  millimeters  respectively.  In  the  willow,  the 
only  species  on  which  this  determination  was  made,  more  than  half  the  total 
expansion  was  in  the  bark,  the  percentages  being,  respectively,  13.5  for  the  bark 
and  2.5  for  the  wood.  To  explain  the  contraction  of  twigs  on  freezing  Wiegand 
suggests:  "When  the  water  is  extracted  from  the  walls  of  the  wood-cells,  the 
latter  contract  to  a  slight  extent  just  as  they  do  when  wood  seasons.  This  ac- 
counts for  a  part  of  the  shrinkage.  The  rest  and  greater  part  occurs  in  the  cortex. 
Here  the  intercellular  spaces  are  quite  large  and  numerous  and  are  normally 
filled  with  air.  When  freezing  occurs  the  ice  forms  in  the  spaces  and  the  cells 
collapse  while  the  air  is  mostly  driven  completely  out  of  the  twig.  The  contrac- 
tion in  the  cortex  will  be  approximately  equal  to  the  volume  of  the  air  expelled 
plus  that  of  the  air  compressed  minus  the  expansion  of  the  ice  while  freezing." 
Curiously  enough  in  all  cases  studied,  except  in  Populus  and  Acer  and  including 
apple,  pear  and  plums,  Wiegand  found  that  buds  increased  decidedly  in  size  upon 
freezing.  Prillieux^^^  demonstrated  conclusively  a  loss  of  air  and  of  weight  in 
frozen  plant  tissues. 

Freezing,  Not  Cold,  Kills. — Most  investigators  do  not  accept  the 
view  that,  aside  from  some  cases  occurring  above  the  freezing  point, 
absolute  cold  kills  any  plant,  whether  by  "shock,"  "cold  rigor"  or  other 
effects.  Again  quoting  Wiegand:  "Most  plants  are  killed  by  the  first 
ice  formation  within  the  tissue.  If  they  survive  this,  a  considerably 
lower  temperature  is  required  to  kill  them,  or  they  may  be  capable  of 
enduring  any  degree  of  cold.  It  has  been  demonstrated  .  .  .  that,  in 
the  case  of  delicate  tissues  at  least,  death  occurs  when  the  ice  formation 
has  progressed  to  a  certain  extent.  .  .  .  Death  seems  due  to  the  actual 
withdrawal  of  water  to  form  ice,  not  to  the  cold.  The  ice  formation 
dries  out  the  cells  and  the  plant  suffers  therefore  from  drought  con- 
ditions. Every  cell  has  its  critical  point,  the  withdrawal  of  water 
beyond  which  will  cause  the  death  of  the  cell,  whether  by  ordinary 
evaporation  or  by  other  means.  It  may  be  supposed  that  the  delicate 
structure  of  the  protoplasm  necessary  to  constitute  living  matter  can  no 


WINTER  KILLING  AND   HARDINESS  253 

longer  sustain  itself  when  too  many  molecules  of  water  are  removed 
from  its  support.  In  the  great  majority  of  plants  this  point  lies  so  high 
in  the  water  content  that  it  is  passed  very  soon  after  the  inception  of  ice 
formation,  hence  the  death  of  many  plants  at  this  period.  Others  may 
be  able  to  exist  with  so  little  water  that  a  very  low  temperature  is 
necessary  before  a  sufficient  quantity  is  abstracted  to  Qause  death. 
From  some  plants  enough  water  cannot  be  abstracted  by  cold  to  kill 
them."  Several  investigators  have  shown  that  certain  tissues,  cooled 
to  a  temperature  which  is  fatal  if  ice  formation  occurs,  will  withstand 
that  same  temperature  if  ice  formation  does  not  occur. 

After  investigating  several  possible  ways  in  which  bud  scales  and  wool 
packing  might  serve  to  protect  the  embryo  flowers  and  shoots  during  the  winter, 
Wiegand  concluded  that  their  main  function  is  not  to  shut  out  cold  or  even  to 
retard  temperature  changes  (about  10  minutes  seemed  the  limit  for  the  greater 
part  of  any  change),  but  rather  to  retard  the  loss  of  moisture  and  to  prevent  me- 
chanical injury  especially  when  the  buds  are  frozen.  Lilac  buds  lost  in  3  days, 
at  temperatures  between  —  18°C.  and  — 7°C.,  2.8  per  cent,  of  water  when  bud 
scales  were  left  on ;  with  bud  scales  removed  the  loss  of  water  was  39  per  cent. 
Heat  absorption  due  to  the  color  of  bud  scales  in  horse-chestnut  buds  amounted 
to  15°F.  Chandler^*  also  found  that  "scales  of  peach  buds  do  not  serve  to 
protect  them  from  low  temperature.  Buds  frozen  in  the  laboratory  with  the 
scales  removed  were  shghtly  more  resistant  to  low  temperature  than  were  buds 
with  the  scales  not  removed." 

Freezmg  and  the  Deciduous  Habit. — The  view  that  death  from  low  tempera- 
tures is  due  to  a  withdrawal  of  water  is  supported  by  the  consideration  that  the 
deciduous  habit  is  in  most  cases  essentially  a  protection  against  water  loss  during 
the  winter  and  that  the  leaves  of  evergreen  plants  are  particularly  adapted  to 
reduce  the  rate  of  transpiration  to  a  minimum. 

An  interesting  and  suggestive  parallelism  exists  between  the  autumnal  be- 
havior of  trees  in  temperate  regions  and  the  changes  in  trees  in  regions  subjected 
to  prolonged  dry  but  warm  weather.  In  both  cases  they  assume  a  distinctly 
xerophytic  character.  The  most  obvious  phenomenon  accompanying  this 
transition  is  leaf-fall.  Of  this  Coulter,  Barnes  and  Cowles^^  say:  "The  leaf 
behavior  of  deciduous  trees  and  of  tropical  evergreens  obviously  is  related  to 
external  factors,  in  the  former  being  associated  with  climatic  periodicity  (either 
of  moisture,  as  in  the  monsoon  forests  of  India,  or  of  temperature,  as  in  the  north- 
ern deciduous  forests),  while  in  the  latter  it  is  associated  with  uniform  moisture 
and  tem.perature.  That  the  deciduous  and  the  evergreen  habits  are  related  to 
external  conditions  may  be  inferred  from  many  trees  and  shrubs  (e.g.,  poison 
i^y,  Virginia  creeper,  various  oaks)  which  shed  their  leaves  in  regions  of  cold 
winters,  but  retain  them  in  warmer  climates;  furthermore,  various  plants  (as 
the  grape  and  the  peach)  become  evergreen  in  uniform  tropical  climates,  and 
even  those  species  that  remain  deciduous  (as  the  persimmon  and  the  mulberry) 
have  much  longer  periods  of  leafage. 

"The  exact  factors  involved  in  leaf-fall,  that  is,  in  the  development  of  the 
absciss  layer,  are  imperfectly  known.     In  the  monsoon  forest  and  in  other  regions 


254 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


of  periodic  drought,  it  is  probable  that  leaf -fall  results  directly  from  the  desicca- 
tion incident  to  the  increased  transpiration  and  decreased  absorption  during  the 
dry  period.  Autumnal  leaf-fall  in  cool  climates  probably  is  due  to  desiccation 
resulting  from  continued  transpiration  at  a  time  when  absorption  is  diminished 
by  reason  of  low  temperature,  although  desiccation  due  to  dryness  in  the  soil  or 
air  may  cause  the  absciss  layer  to  develop  in  early  summer.  A  severe  frost  in 
early  autumn  may  retard  leaf-fall  through  injury  to  the  tissues  that  develop  the 
absciss  layer. 


"The  shedding  of  leaves  at  the  inception  of  a  cool  or  dry  period  is  of  inestima- 
ble advantage,  especially  in  trees  with  delicate  leaves,  because  of  the  enormously 
reduced  transpiration  thus  resulting.  The  leafless  tree  is  one  of  the  most  per- 
fectly protected  of  plant  structures,  since  impervious  bud  scales  and  bark  cover 
all  exposed  portions." 

Accompanying  leaf-fall  the  moisture  contents  of  the  various  tissues 
change.  From  summer  to  early  winter  there  is  a  considerable  lowering 
of  the  moisture  percentage  as  shown  in  Table  11,  adapted  from  data  by 
Baake  et  al.,^  showing  the  moisture  percentage  in  twigs  of  several  varieties 
of  apple. 

Table  11. — Percentage  Moisture  Content  of  Apple  Twigs 


Dormant 


Bud 
swelling 


Blossom- 
ing 


Summer 
growth 
period 


Wood 
ripening 


Hibernal 

Oldenburg 

Wealthy 

Yellow  Transparent . . . . 

Mcintosh 

Red  Astrachan 

Jonathan 

Winesap 

Grimes 

Ben  Davis 

Average,  17  varieties 


42.43 
45.64 
45.04 
46.32 
46.82 
47.30 
43.52 
47.58 
48.23 
47.76 

45.765 


48.65 
53.31 
51.66 
52.10 
50.52 
54.86 
52.00 
50.57 
49.54 
51.94 


65.53 
62.15 
65.57 
61.87 
65.79 
62.62 
64.48 
65 .  22 
63.20 


58.98 
60.50 
61.11 
61.49 
57.76 
60.82 
58.77 
58.67 
58.95 
59.44 


52.56 


64.19 


58.92 


53.67 
52.98 
55.04 
51.88 
55.31 
51 .  63 
51.53 
54.16 
51.09 

52.55 


INCREASING  HARDINESS 

By  Increasing  Sap  Density. — A  logical  consequence  of  the  theory  of 
death  through  withdrawal  of  water  by  freezing  is  the  correlation  of  an 
increased  sap  density  (molar  concentration)  with  a  lower  killing  tem- 
perature for  any  given  species.  Chandler's  investigations  have  demon- 
strated this.  Sap  density  was  increased  by  various  means,  such  as  with- 
holding water,  watering  with  mineral  solutions,  inducing  absorption  of 
various  substances  and  it  was  reduced  by  shading;  in  each  case  with 


WINTER  KILLING  AND  HARDINESS  255 

greater  density  there  was  greater  hardiness.  Unfortunately,  attempts 
to  increase  sap  density  and  therefore  hardiness,  in  peach  trees,  cabbage 
and  tobacco  plants,  by  heavy  applications  of  potash  fertihzers  were 
not  successful  in  attaining  either  object. ^^  European  writers  have 
claimed  increased  hardiness  from  phosphate  or  potash  applications; 
their  evidence,  however,  is  not  entirely  convincing. 

Wilted  tissue,  presenting  another  case  of  increased  sap  density  through 
withdrawal  of  water,  was  tested  for  hardiness  by  Chandler  with  no 
significant  results.  This  seems  entirely  consistent  since  the  sap  density 
in  this  case  is  the  result,  not  of  the  addition  of  substances  in  solution,  but 
rather  of  the  withdrawal  of  water  and  may  be  closely  comparable  to  the 
initial  stage  of  freezing  itself.  When  a  longer  and  slower  wilting  appeared 
to  be  induced  on  dormant  peach  twigs,  possibly  resulting  in  a  somewhat 
more  fundamental  change  in  the  protoplasm,  hardiness  seemed  increased. 

By  Increasing  Water-retaining  Capacity. — Another  consequence  of 
the  theory  that  death  is  due  to  the  withdrawal  of  water  from  the  cell 
and  later  from  the  tissue,  is  that  resistance  to  cold  must  be  increased  by 
factors   tending   to   increase  the  water-retaining  capacity  of  the  cells. 

Observations  on  the  moisture  content  of  apple  twigs  reported  by 
Beach  and  Allen,  ^^  shown  in  Table  13,  reveal  an  important  relation  to 
hardiness.  From  July  to  December  there  is  considerable  variation  in  the 
moisture  content  of  the  several  varieties.  On  Jan.  15,  however,  following 
several  days  of  severe  cold,  the  two  hardiest  varieties.  Hibernal  and 
Wealthy,  have  a  noticeably  higher  moisture  content  than  the  tenderer 
varieties;  furthermore,  the  loss  of  water  from  July  to  January  is  very 
much  less  in  these  two  hardiest  varieties  than  in  the  others. 

Data  of  similar  purport,  drawn  on  for  Table  12,  are  reported  by 
Strausbaugh^^^  in  Minnesota.  Water  losses  accompanying  markedly 
cold  weather  were  greater  in  the  less  hardy  plums.  Following  a  period  of 
relatively  warm  weather  the  less  hardy  varieties  showed  a  marked 
increase  in  moisture  content,  possibly  because  they  were  less  dormant, 
possibly  because  they  had  lost  more. 

These  observations  indicate  that  the  actual  moisture  content  of  a 
tissue  at  most  times  has  less  connection  with  hardiness  than  its  water- 
retaining  capacity.  The  water  lost  is  less  significant  than  the  water 
retained.  Protection  against  injury  from  low  temperatures  depends  on 
the  amount  of  water  the  plant  can  retain  at  a  critical  moment  against  the 
great  force  which  tends  to  draw  water  out  of  the  cells  to  form  ice  crystals 
in  the  intercellular  spaces.  This  force  can  be  appreciated  by  the  familiar 
ability  of  growing  ice  crystals  to  split  rocks.  To  hold  water  against  this 
influence,  the  protoplasm  must  have  a  certain  amount  of  its  moisture 
supply  in  a  form  which  is  not  easily  frozen.  In  the  section  on  Water 
Relations  plant  tissue  is  shown  to  contain,  in  addition  to  its  free  and  readily 
frozen  water,  water  in  an  adsorbed  or  colloidal  state,  which  does  not 


256 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Table  12. — Changes  in  Water  Content  of  Fruit  Buds  of  Several  Varieties 

OF  Plums 
(Arranged  from  Straushaugh^^^) 


Stella 
(semihardy) 

Tonka 
(semihardy) 

Assiniboine 
(hardy) 

Nov.  19 

Dec   1                

50.38 
43.51 

6.87 

50.51 

43.93 

6.58 

46.51 
45.49 

1.02 

Dec.  26 

49.30 
5.79 

50.70 

6.77 

46.80 

Increase 

0.86 

Jan    16                                         

45.98 

44 .  34 

1.64 

44.41 

39.16 

5.25 

47.36 

Jan   23                               

47.31 

Loss                                    

0.05 

Feb.  21 

Mar.  5              

41.98 

39.78 

2.20 

43.24 
40.46 

2.78 

46 .  83 
46.16 

0  67 



Loss  Nov.  19  to  Mar.  5 

10.60 

10.05 

0.35 

Table  13. — Moisture  Content 

OF  Apple 

Twigs  on  Different 

Dates  le 

Variety 

July  15 

Nov.  15 

Dec.  26 

to  28 

Jan.  15 

Decrease 

July  15  to 

Jan.  15 

Delicious 

Gano 

60.3 
57.2 
60.7 
53.5 
60.4 

50.5 
53.2 
52.0 
50.4 
50.6 

50.5 
51.2 
57.7 
52.0 
51.0 

42.5 
44.3 
43.6 
46.8 
47.5 

17.8 
12.9 

Grimes                     

17.1 

Hibernal              

6.7 

Wealthv                    

9.0 

freeze  except  at  temperatures  ranging  to  —  78°C.  If  a  plant  tissue  con- 
tains enough  adsorbed  water,  it  presumably  can  withstand  any  winter 
temperature.  Its  free  water  freezes,  but  there  is  enough  water  which  is 
not  readily  frozen  to  maintain  the  hfe  of  the  protoplasm. 

It  seems  paradoxical  that  tender  plant  tissues  usually  contain  more 
water  than  those  which  are  hardier.  In  fact  Johnston  found  the  ratio 
of  water  content  to  dry  weight  of  fruit  buds  a  fairly  good  index  of  the 
relative  hardiness  of  certain  peach  varieties  and  similar  observations  have 
been  made  by  many  other  investigators.  However,  it  is  shown  presently 
that  the  development  of  the  water-retaining  capacity  follows  as  a  reaction 
to  a  diminished  water  supply.     Hence,  there  is  a  direct  relation  between 


WINTER  KILLING  AND  HARDINESS  257 

the  lower  total  water  content  of  hardy  tissues  and  their  greater  content  of 
adsorbed  water  which  is  not  readily  frozen.  Furthermore,  the  water- 
holding  capacity  operates  less  effectively  in  dilute  solutions.  ^'^'* 

Water  in  the  adsorbed  or  colloidal  condition  cannot  hold  materials  in 
solution  but  may  cause  higher  results  in  sap  density  determinations. 
Since  in  hardy  plants  there  is  a  smaller  amount  of  free  water  which  can 
hold  materials  in  solution,  the  sap  solutes  must  be  held  ordinarily  in  a 
more  concentrated  solution  than  in  tender  plants.  Hence  the  correlation 
between  sap  density  and  hardiness  found  b}'  Chandler  and  confirmed  by 
other  investigators;  however,  since  there  is  no  direct  causative  relation 
between  hardiness  and  sap  density,  it  sometimes  happens  that  the  correla- 
tion does  not  hold.  Pantanelli,^"  for  example,  was  unable  to  find  a 
relation  between  resistance  to  cold  and  molecular  concentration  (sap 
densitjO  with  wheat  or  beets,  though  the  correlation  held  for  sunflower, 
tomato  and  corn. 

Clear  distinction  is  necessary  between  cell  water  loss  and  tissue 
water  loss.  Cell  water  loss  is  the  cause  of  death  by  freezing.  Tissue 
water  loss  must,  in  many  cases,  accentuate  cell  water  loss  and  thus 
indirectly  lead  to  killing.  Though  the  two  forms  are  distinct,  in  most 
cases  each  promotes  the  other.  It  is  probable  that  some  plants  are  reten- 
tive of  cell  water  and  not  of  tissue  water,  hence  hardy  but  not  drought 
resistant;  others  are  presumably  retentive  of  tissue  water  but  not  of  cell 
water,  hence  drought  resistant  but  not  hardy.  However,  there  is  a 
strong  tendency  toward  parallelism  in  drought  resistance  and  cold  resis- 
tance.    The  data  presented  above  are  based  on  this  parallelism. 

Xerophytic  adaptations  are  well  known  to  students  of  morphology; 
they  serve  primarily  as  protection  against  tissue  loss,  but  may  have  an 
ultimate  bearing  on  cell  loss  and  therefore  on  hardiness.  Strausbaugh'^^ 
shows  that  the  lenticel  area  on  the  twigs  of  a  semihardy  plum  is  from 
three  to  six  times  that  of  a  hardy  variety.  He  shows  also  a  greater  loss 
of  water  from  the  twigs  of  a  tender  than  from  those  of  a  hardy  variety. 
Thus,  occasionally,  morphological  differences  may  influence,  though 
indirectly,  cell  water  loss.  Rather  extensive  investigations,  however, 
have  failed  to  establish  consistent  morphological  differences  between 
hardy  and  tender  varieties.  Cell  water  loss,  then,  must  depend  on 
something  other  than  structure. 

Water-retaining  Capacity  Associated  with  Pentosan  Content. — 
Plant  tissue  which  withstands  freezing  must  be  supposed  to  contain  or  be 
able  to  manufacture  substances  which  will  hold  water  in  an  adsorbed  or 
colloidal  condition.  These  substances  must  themselves  be  colloids,  they 
must  have  a  great  water-holding  and  water-absorbing  capacity,  they  must 
be  known  to  occur  in  practically  all  plants  capable  of  withstanding  winter 
conditions  and  they  must  be  distributed  generally  through  practically  all 
plant  tissues.     The  compounds  which  answer  best  to  these  specifications 

17 


258 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


are  the  pentosans,  more  particularly  the  water  soluble  pentosans.  Evi- 
dence is  presented  in  the  section  on  Water  Relations  to  show  that  pentosans 
of  some  sort  are  probably  the  compounds  holding  water  in  an  adsorbed  or 
colloidal  condition  in  plant  tissues;  this  is  confirmed  by  determinations  of 
Hooker, '*'*  given  in  Table  14,  which  show  a  correlation  between  pentosan 
content  and  hardiness. 


Table  14. 


-Pentosan  Content  of  Plant  Tissues  in  Terms  of  Fresh  Weight^^ 
(1920  Wood) 


Nov.  g 

,  1920 

Dec.  2 

,  1920 

Bases, 
per  cent. 

Tips, 
per  cent. 

Bases, 
per  cent. 

Tips, 
per  cent. 

Wealthy 

6.52 
5.15 
3.29 

4.72 
5.64 
3.90 

5.41 
3.55 
4.37 
3.28 
5.19 
3.22 

5.99 
5.89 
5.01 
5.26 
5.59 
4.04 

5.11 

Yellow  Transparent 

Missouri  Pippin 

5.06 
4.91 

Stayman  Winesap 

Ben  Davis  (short  shoots — mature) .  .  . 
Ben  Davis  (long  shoots— immature) . 

3.96 
4.56 
3.79 

Currant                                       

4.78 
5.20 
1.61 

4.44 
3.09 

1.28 

5.01 

4.28 
killed 

3.68 

Cuthbert  raspberry  (mature) 

Cuthbert  raspberry  (immature) 

3.24 
killed 

This  evidence  supports  the  idea  that  pentosans  largely  determine  the 
water-retaining  capacity  of  plant  cells,  though  the  particular  compounds 
concerned  remain  to  be  determined. 

Water  Soluble  Pentosans  in  Particular. — Water  soluble  pentosans, 
such  as  gums  or  pectins,  seem  the  most  likely  to  act  as  water-retaining 
substances.     Studies  by  Rosa  indicate  that  this  is  the  case.     Some  of  his 


Table  15. 


-Soluble  and  Insoluble  Pentosans  in  Cabbage  and  Tomato 

{After  Rosa'^') 


Total 
pentosan 


Hot-water- 
soluble  pectin 


Insoluble 
(by  difference) 


Cabbage : 

Tender 

Hardy  (dry  grown) . . 

Hardy  (by  exposure) 
Tomato: 

Tender 

Dry  grown 

Exposed 


0.215 
0.423 
0.530 

0.693 
0.720 
0.682 


0.075 
0.292 
0.408 

0.070 
0.071 
0.071 


0.140 
0.131 
0.124 

0.623 
0.649 
0.611 


WINTER  KILLING  AND  HARDINESS 


259 


data,  reported  in  Table  15,  show  the  tomato  to  have  a  higher  total 
pentosan  content  than  the  hardier  cabbage,  but  the  soluble  pentosans 
are  quite  differently  arranged.  The  increase  of  total  pentosans  in 
cabbage  of  differing  degrees  of  hardiness  is  due  entirely  to  the  increase 
in  soluble  pentosans;  with  the  tomato,  in  which  no  treatment  materially 
increases  hardiness,  there  is  no  increase  in  soluble  pentosans. 

Investigation  is  likely  to  show  that  other  substances  may  exercise 
water-retaining  properties  and  therefore  tend  toward  hardiness.  Fat 
emulsions  conceivably  may  act  in  this  way. 

Whatever  the  compounds  may  prove  to  be,  their  water-adsorbing 
power  undoubtedly  is  affected  to  a  marked  degree  by  the  factors  which 
generally  increase  or  decrease  the  water-retaining  properties  of  colloids. 
The  effects  of  nitrogenous  compounds  and  hydrogen-ion  concentration 
on  hardiness  have  been  emphasized  by  Harvey  and  may  be  of  a  similar 
nature. 

Pentosan  Content,  Water-retaining  Capacity  and  Hardiness  Respon- 
sive to  Environmental  Conditions.^ — The  water-retaining  capacity  of 
plant  tissues  is  increased  by  any  condition  which  limits  the  water  sup- 
ply without  producing  actual  injury.  This  is  discussed  in  the  section 
on  Water  Relations.  Rosa  presents  data,  given  in  Table  16,  showing 
an  increase  in  the  pentosan  content  of  plants  hardened  by  exposure  to 
low  temperatures  in  a  cold  frame.  This  indicates  also  that  the  hardening 
or  maturing  of  plant  tissue  by  exposure  to  cold  is  essentially  a  reaction  to 
a  limited  water  supply. 


Table  16. — Pentosans  of  Vegetable  Plants  in  Percentages  of  Fresh  Weight 

{After  Rosa^^^) 


Cabbage 


Leaf  lettuce    Cauliflower 


Moisture,  series  on  greenhouse  plants 

1.  Tender  plants  grown  in  wet  soil 

2.  Medium  hard}'  plants  grown  with  moder- 

ate moisture  supply 

3.  Hardy  plants  grown  in  dry  soil 

4.  Hardy  plants,  partly  wilted  for  2  weeks .  .  . 

Coldjrame  series 

1.  Tender  greenhouse  plants 

2.  Hardened  1  week 

3.  Hardened  2  weeks 

4.  Hardened  3  weeks 


0.191 
0.403 


Rosa  shows  also  that  there  is  a  fairly  constant  increase  in  the  pentosan 
content  of  vegetables  from  early  fall  until  the  plants  are  killed  by  cold. 
The  data  in  Table  17  indicate  that  maturity  is  associated  with  increased 
pentosan  content  and  greater  water-retaining  capacity. 


260 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Table  17. — Pentosan  Content  of  Garden  Plants  in  Percentages  op  Fresh 

Weight'"'' 


Date 

Kale 

Cabbage 

Celery 

Oct.      7 

0.511 
0.528 
0.537 
0.722 
1.064 

0.289 
0.580 
0.545 
0.621 

0.782 

0.567 

Oct.    20   

0,801 

Nov.    3 

0.793 

Nov   10                              

1  029 

Nov   18                     

Increased  Hardiness  with  Increased  Maturity.^ — The  most  generally 
recognized  and  most  potent  single  factor  influencing  killing  by  cold, 
particularly  in  tissues  withstanding  a  fair  amount  of  freezing,  is  the 
degree  of  maturity  attained  at  the  time  of  exposure.  So  widely  is  this 
state  recognized  in  field  conditions,  that  experimental  evidence  on  this 
point,  though  available,  is  hardly  necessary.  Some  less  known,  but 
widely  occurring,  phases  of  immaturity  in  trees  are  considered  later. 
The  greater  susceptibility  of  immature  tissue  to  injury  from  cold  is  due, 
in  part,  to  the  fact  that  pentosans  or  other  water-retaining  substances 
have  not  developed :  The  greater  water  content  of  such  tissue  is  evidence 
of  the  lack  of  those  drying  conditions  necessary  for  the  proper  develop- 
ment of  pentosans  and  hence  of  maturity.  Chandler  found  no  constant 
difference  in  the  moisture  content  of  the  twig  cortex  during  the  winter, 
though  its  hardiness  varied  considerably.  With  reference  to  density  he 
states:  "It  would  seem  certain  then  that  while  a  part  of  the  increased 
hardiness  of  tree  tissue  in  winter  may  possibly  be  accounted  for  by  the 
greater  sap  density,  not  all  of  it  can ;  certainly  not  the  greater  hardiness  of 
December  tissue  over  that  of  October."  The  same  investigator  offers  the 
following  suggestion  based  on  experimental  evidence;  "It  would  seem 
highly  probable  that,  except  in  the  case  of  cambium,  the  additional  hardi- 
ness acquired  by  the  different  tissues  of  the  trees  as  they  pass  into  winter, 
is  a  change  in  the  protoplasm  such  that  it  can  withstand  the  great  loss 
of  water  rather  than  a  change  in  the  percentage  of  moisture  or  in  sap 
density." 

RAPID  TEMPERATURE  CHANGES 

Since  maturity  is  a  reaction  to  dry  conditions  whether  produced  by 
exposure  to  cold  or  by  actual  limitation  of  the  water  supply,  it  is  logical 
to  expect  distinct  differences  in  the  amount  of  injury  produced  by  rapid 
freezing  when  no  time  is  allowed  for  the  development  of  pentosans  and 
by  a  gradual  reduction  of  temperature  permitting  an  increase  in  the 
water-retaining  capacity  of  the  tissue  to  develop. 

Killing  with  Slow  and  with  Rapid  Freezing. — The  injurious  effects 
of  rapid  freezing  seem  to  have  received  little  attention  until  the  recent 
work  of  Winkler  and  of  Chandler, 


WINTER   KILLING  AND  HARDINESS  261 

Winkler, 217  working  with  dormant  twigs  that  killed  at  —  22°C.  upon  rapid 
freezing,  found  that  by  small  successive  reductions  of  temperature,  at  —  16°C. 
for  3  days,  at  -18°C.  for  2  days,  at  -20°C.  for  3  days,  at  -22°C.  for  2  days, 
at  — 25°C.  for  3  days,  the  twigs  were  enabled  to  withstand  12  hours  of  freezing 
at  from  —  30°C.  to  —  32°C.  Chandler^**  reports  on  the  results  of  his  work, 
in  part,  as  follows:  "The  rate  of  temperature  fall  is  very  important  indeed, 
especially  in  case  of  winter  buds.  In  fact  apple  buds  can  be  frozen  in  a 
chamber  surrounded  by  salt  and  ice  rapidly  enough  that  practically  all  of  them 
will  be  killed  at  a  temperature  of  zero  F.,  or  slightly  below,  while  it  is  well  known 
that  they  may  go  through  a  temperature  of  20°F.  to  30°F.  below  zero  with  but 
slight  injury  where  the  temperature  fall  is  not  so  rapid  .  .  .  the  killing  tem- 
perature of  rapidly  frozen  twigs  was  four  and  a  half  degrees  higher  than  that 
of  the  more  slowly  frozen  twigs,  and  even  then  the  buds  of  the  rapidly  frozen 
twigs  killed  the  worst,  .  .  .  rapid  falling  in  the  early  part  of  the  freezing 
temperature  down  to  —  12°C.,  does  more  harm  than  rapid  fall  in  the  latter  part 
of  the  period,  from  —  12°C.  to  the  killing  temperature."  "Many  young  fruits 
and  succulent  plants  were  also  frozen  slowly  and  rapidly  but  there  was  so  little 
apparent  difference  betAveen  the  results  that  the  data  are  not  given.  The  killing 
temperature  lies  so  near  the  freezing  point  that  possibly  the  slowly  frozen  tissue 
kills  badly  because  it  is  exposed  to  temperatures  around  the  killing  point 
longer."  "...  the  rate  of  temperature  fall  with  winter  twigs  and  buds  ex- 
erts the  greatest  influence  on  the  extent  of  killing  at  a  given  temperature  of  any 
feature  we  have  so  far  discussed.  And  in  the  case  of  very  forward,  rather  tender, 
fruit  buds,  the  rate  of  temperature  fall  exerts  great  influence.  Thus  on  March 
24,  1913,  when  all  buds,  especially  the  peaches,  plums  and  cherries,  had  made 
much  growth,  a  temperature  of  —  11.5°C.  killed  as  many  buds  with  rapid  tem- 
perature fall  as  a  temperature  of  —  16.5°C.  with  a  slower  temperature  fall." 

A  factor  involved  in  very  rapid  lowering  of  the  temperature  is  the 
possibility  of  ice  formation  within  the  cells.  Though  the  rate  of  tem- 
perature fall  involved  probably  does  not  occur  in  nature,  it  may  have 
been  produced  in  some  of  the  experiments  just  described. 

Slow  and  Rapid  Thawing. — Practical  men  have  long  held  that  rapid 
thawing  intensifies  damage  from  low  temperatures  and  many  investi- 
gators have  accepted  this  view.  The  fruit  grower  who  heats  his  orchard 
during  the  cold  nights  of  the  growing  season  tries  just  as  carefully  to 
keep  the  early  morning  sun  from  the  blossoms;  the  young  florist  is  taught 
by  older  men  to  supply  heat  very  slowly  if  accident  has  lowered  the 
temperature  of  the  greenhouse  to  a  critical  point. 

Wiegand^i*  found  that  thawing  generally  occurs  at  temperatures 
below  0°C.,  or  about  at  the  freezing  point  (-3.5°C.  to  -2.3°C.  for  buds). 
Sudden  thawing  or  several  rapid  alternations  of  freezing  and  thawing 
did  not  seem  injurious. 

It  has  been  held  that  rapid  thawing  induces  excessive  transpiration 
and  prevents  the  return  into  the  cell  of  the  the  sap  withdrawn  in  freezing. 
The  trend  of  opinion  among  recent  investigators,  how^ever,  fails  to  support 


262  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

this  view,  it  having  been  found  to  hold  only  in  a  very  few  cases.  As 
already  indicated,  it  can  be  shown  definitely,  sometimes  at  least,  that 
death  occurs  before  any  thawing  begins;  furthermore,  the  method  used 
by  Sachs  and  much  in  vogue  among  gardeners  to  induce  slow  thawing, 
namely,  immersion  or  sprinkling  with  water,  is  in  reality  a  method  leading 
to  more  rapid  thawing  than  would  occur  in  air.  The  water  causes  a  coat- 
ing of  ice  on  the  exterior,  thus  liberating  heat  to  the  tissue.  Though  ob- 
jections might  be  adduced,  to  this  view,  the  chief  matter  of  interest  here 
is  that  investigators  have  found,  in  practically  all  cases,  no  difference 
in  killing  to  ensue  whether  the  thawing  be  rapid  or  retarded.  It  should 
be  pointed  out,  however,  that  there  are  no  reports  of  inquiry  into  the 
effect  of  sunlight  on  frozen  tissue.  Injuries  due  to  the  effect  of  light 
on  frozen  tissue  might  easily  be  attributed  to  rapid  thawing.  There 
seems  to  be  enough  evidence  in  field  conditions  of  association  of  sunlight 
and  injury  to  warrant  careful  study,  particularly  in  view  of  the  increased 
permeability  known  to  accompany  increased  light. 

VARIATION  IN  CRITICAL  TEMPERATURES 

Definite  evidence,  under  experimental  conditions,  has  shown  that 
the  critical  temperature  at  which  killing  results  is  not  a  definite  point 
for  any  species,  variety  or  individual  plant  but  is  the  result  of  a  complex 
of  conditions.  It  probably  depends  to  a  great  degree  on  water-retaining 
capacity  or  the  amount  of  water  present  that  is  not  readily  frozen,  but 
other  factors  may  be  equally  important  under  certain  circumstances 
and  unquestionably  there  are  a  number  of  factors  affecting  the  water- 
retaining  capacity  of  the  cell  colloids.  All  of  these  may  constantly  be 
fluctuating  more  or  less  independently  of  one  another  and  their  product, 
the  killing  temperature,  must  therefore  assume  many  different  values. 
This  is  abundantly  borne  out  in  field  observations  of  winter-killing. 

Summary. — The  most  tenable  of  the  theories  explaining  killing  from 
cold  ascribes  death  to  dehydration  of  the  cells.  Ice  formation  generally 
begins  in  the  intercellular  spaces  and  the  process  draws  water  from  the 
cells.  The  water  is  withdrawn  gradually,  each  decrease  in  temperature 
being  followed  by  further  water  loss  from  the  cells,  though  the  rate  of 
this  loss  becomes  progressively  lower.  Death  occurs  when  the  dehydra- 
tion proceeds  beyond  a  certain  point.  The  increasing  density  of  the 
cell  sap  with  continued  water  loss  tends  to  hold  the  remaining  water  more 
tenaciously  and  thus  protects  the  cell  somewhat  against  further  loss 
and  eventual  death.  The  cell  colloids,  particularly  the  water  soluble 
pentosans,  operate  in  the  same  direction  and  play  a  still  more  important 
part.  These  substances  (the  water  soluble  pentosans)  develop  in  some 
plants  in  response  to  certain  environmental  conditions — particularly 
decreasing  temperature  and  a  decreased  moisture  supply.     These  facts 


WINTER  KILLING  AND  HARDINESS  263 

suggest  that  certain  cultural  treatments  may  be  employed  to  increase 
the  hardiness  of  plant  tissue.  Rapid  freezing  is  probably  more  danger- 
ous than  slow  freezing  to  plant  tissue  because  there  is  not  time  for  the 
plant  to  develop  a  greater  water-retaining  capacity;  consequently  it 
loses  a  larger  percentage  of  its  moisture  at  a  given  temperature.  Con- 
trary to  general  belief  there  is  little  evidence  that  rapid  thawing  is  more 
injurious  than  slow  thawing.  However,  this  should  not  be  taken  to 
mean  necessarily  that  rapid  thawing  in  bright  sunshine  is  not  more 
injurious  than  slow  thawing  under  cloudy  conditions,  since  the  increased 
permeability  accompanying  increased  light  may  have  an  influence. 
Critical  temperatures  for  a  given  species  will  vary  considerably  with 
conditions. 


CHAPTER  XVI 
WINTER  INJURY 

Macoun'2o  enumerates  ten  manifestations  of  winter  injury  in  orchard 
fruits,  viz.:  root-killing,  bark-splitting,  trunk-splitting,  sunscald,  crotch 
injury,  killing  back  of  branches,  black  heart,  trunk  injury,  killing  of 
dormant  buds  and  winter-killing  of  swollen  buds.  As  one  form  of  bark- 
splitting,  Macoun  includes  a  condition  considered  here  as  crown  rot. 
These  forms  may  occur  singly  or  in  varying  combinations;  some  are 
products  of  severe  conditions  that  almost  of  necessity  entail  other  forms 
characteristic  of  less  severe  freezing;  some  may  be  responses  of  varying 
plant  conditions  to  the  same  weather  and  some  may  be  responses  of 
identical  plant  conditions  to  varying  weather.  Still  other  manifestations 
are  recorded  occasionally. 

Conditions  Accompanying  Winter  Injury. — Nine  of  the  ten  forms  of 
winter  injury  distinguished  by  Macoun ^^'^  appear  above  ground.  This 
diversity  is  due  probably  to  a  wider  range  of  internal  conditions  in  the 
tops  and  to  a  wider  range  in  above-ground  environmental  factors.  It 
may  be  attributed  also  to  the  greater  facility  with  which  top  injuries  are 
studied;  were  observations  of  parts  below  ground  more  easily  made, 
what  is  now  referred  to  simply  as  root  injury  might  be  found  to  consist  of 
several  kinds.  Above  ground  so  diverse  are  the  manifestations  of 
winter  injury  that  the  whole  condition  seems  confusion  confounded, 
abounding  in  contradictions.  Certain  trees  in  an  orchard  suffer  winter 
injury  and  others  do  not.  Excess  soil  moisture  causes  winter  injury  in 
one  instance  and  lack  of  soil  moisture  causes  it  in  another.  Cold  leads 
directly  to  winter  injury  yet  sometimes  high  temperatures  induce  it 
hardly  less  directly.  At  times  young  trees  suffer  more;  at  others,  older 
trees.  Orchards  in  high  wind-swept  spots  are  damaged;  again  it  is  the 
low-lying  orchards  that  are  afflicted.  Late  maturing  trees  suffer  in  one 
locahty;  somewhere  else  it  is  the  early  maturing  trees.  Now  it  is  trees 
weakened  by  neglect  that  lack  hardiness;  again  it  is  the  highest  cultivated 
trees  that  fail.  An  early  winter  freeze  is  the  cause  at  one  time;  in  another 
case  a  late  winter  freeze  brings  destruction.  An  early  freeze  has  been 
known  to  kill  peaches  while  pecans  survived. 

Table  18,  arranged  from  data  assembled  at  the  New  York  Agri- 
cultural Experiment  Station,  at  Geneva''*"  and  showing  climatic  condi- 
tions at  that  point,  is  designed  to  show  the  varying  conditions  that  may 
induce  or  accompany  winter  injury.  Unusual  climatic  features  that 
have,    conceivably,    a   bearing  here,   are   shown   in   heavy   type.     The 

264 


WINTER  INJURY 

©vnOOOO'O'OWO'OOO'fflOOO'OOOOOOOOOOOOOOOOOO     • 
t,^  ^  ^  -.^V'  ^-'  0>  C^'  C^'  '^'  00  ^'  iH  i«  C<i  (»  C  M  M  ■^  W  «  ^^  TP  »*'  rt  M  •>1<  O  O  ^  O  00  00  ^1     ■ 

oot-ooooooooou»>oooooooooooooooooooooo    ■ 
^o«dobodtD^o'o5^'OC)'--<■*'<oc<3■*'3<c^C'lc^^c~^-tc^'^■odo5^-oC'--|<^^ooococO'^o 

7  MM  m"7 Ti    7mm7     mi    7; 

ISUaC  OOOOOOt^'CINOOOOOOOOOOOOiOOO'OOOOOOOO     • 

|7      M  III  I       M    M       l"  l"  1  I     : 

OOOOOOOOOOOOOOiCinOOOOOOOOOOOOOOOOOOOO     • 

OOOinMOMOO-HOOOOOOOOOOOOIOOOOOOOOOOOOO     ■ 

lr^mln^^^4o^^He^^N^M'lOMo6oio'--ltoo6odoio6MOO-t•^^^-'o^5rtO)«o0505«p    • 
c»3*05(NoO'-<05C<505co<off>'^'-ioO'<j<(0>OM-H>-(a5r-(mN'0'-io«oot-iO'nN'*J~« 

c53Nc5NS53S<NSS?5S(N(NW<Nr-,iN(N(N--llN.--i(NIN(N<N(Nrt»H(Nrt(N(N(N 
OtD«0(N^i-iM05r)<IOt^00'»iNN'-<O--Wt^O>00>00>05t~'-<O0>t^-*>'5Oc0OrH 

mC^00lMON(N-#>0<N>niOTl<.-(M0JOI^l^f~M'OO'-iC0f)t^lOi-i05OOiOOiOTt( 
t^'t-^t^'c^'N^C^»O'-<iC»ON!^^t^O5t^O00t^tOC0'M(N':D^^O5>0»Hi000W^MMC>C0 

r-<iC(W00OTj<«tD'J<O(NOO05t^O!0:— i«<JMiM0!«0CTit^OIOt-C0'OIOC<I>-lO«0O 

(3>tdo5td^~^030^^odu5o6tdo5MoiN^od'-^^«©td<D^^Nio6o^lo<Ol^l^05■--lOlOoc 
to  o  oj  oi  w  M  ^  <Ti  00  d  c<i  (N  o  «i  c^'  |^^  pi  ^•  -H  «'  c^'  00  M  -H  r-^  oi  h-'  CO  o  ro  ^  "O  IN  00  >o  o 

WMMOOt-C^iO— "MC<lO05r^C<lC0OtC"-iO«0-f0ir^W-»<Oi0!MC0^M1"OO— "t 

coir!Qo^t-c^doo''-*oO'^^dc'UOOO'^«o-^'-'CCt--fC*cocoMOO'-'^»otDON 

SoiOCDIOtOcCOOcOiOCOCOtDOOtOOOIOCOffiOIOtOWOtOtOtOcOtDCOCOCCO 
«0050'OOOOr^'Ot>00  00(NOCOOCO»H0010(Mt^OOTt>OOOOC;;DO'0-OOIO'0-J 

iodioN^do6dt^oddocd'-<dh^--<'H'»'--'t^ioodo6e«o6oodo5dooooi^ei>oqj 

3o3to3ScOCDCOO«3tOt^l^tOt^t^t"t^O«OOtOt-lC-.Ct^tOt^Ot^t^Ot-t^«0 

ot^ooo5'*t^M>ii'io-i'0505NOeoM03'ra>n?iO!gotoocM«Mt>-C2coio^2^o 
»5;ooo^~^-^c<3lOcDcolQ'n^•cq^-cc^o«Drocc-^otO'ra•*^^^Ht^M1lO'0'*'^^e<^'0 

C^t-.-H.-<IOMO«Ht-Cv)00^-*t^OOC0^O00Ot0OOroOJ105'^2-j;<N00iONN 
^rtrtC0t-t^>O00^'-HCD«DO:MC<300(MO>'f<00e0iMO2-Ht^cOC^)(N(N08tDtDt^-H00Tf 

C>i  M  M  C<j  O  C^  (N  O  d  i-H  M  ^  d  Tf<  N  -H  N  e>  N  C^  --I  M  "-I  C^  <N  ■-*  IN  W  CO  lO  M  --H  1-H  C^ 

N.-^C^CDC0fN00'#c0t^00C<lOC0r^OIO^W^*'H:0^00IO0>^^t*O^Hif3loOl^tf>O 

c4'^l6c^m•^r^rile6■^'6'^^cim'^nr^'-^i6c^t•^^nr^r-l(^ldc(ioi•-^ttil6n■Hn 

o  o  o  ■ 

Tl'U50I^OOOO-<iNCO'*'OCOt^0005  0^(NC^'^'ra!01^QOro— '-(MCO-^iOOtj-OO^ 

c<5-i'iOcDt--oco:0'^c^c<5TfiotDr^oociO— "Mco-rmcot^oooo  —  ojeorfiotot^M 
00 ao 00 00 00' 00 ooc:;050>030s020Ci05030000000000'-i-<^— i'"'--'^^  ra 

OOOOOOXOOOOOOXXXOOOO«0000(»0003C50)05050S05C:01050:050>010>010!OSS; 


265 


266  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

highest  and  the  lowest  rainfalls  for  August,  September  and  October,  the 
highest  mean  temperatures  for  August,  September  and  October  and 
the  lowest  mean  temperatures  from  October  to  February  are  thus  distin- 
guished and  the  minimum  temperatures  for  each  month  indicated. 
The  winters  of  1895-1896,  1903-1904  and  1917-1918  may  be  considered 
the  seasons  of  greatest  winter  injury  for  this  section  in  recent  years. 
It  is  evident  at  once  that  the  rainfall  preceding  the  winter  of  1895-1896 
was  the  lowest  of  any  season  reported;  that  preceding  the  1903-1904 
season  was  the  highest  and  that  preceding  the  1917-1918  winter  was  very 
close  to  an  average.  The  three  destructive  winters  were,  then,  preceded 
by  both  extremes  and  an  average  rainfall.  Though  the  rainfall  for  the 
months  considered  was  in  1897  only  0.02  inch  more  than  that  of  1896,  no 
serious  damage  was  reported;  though  the  rainfall  for  these  months  in 
1915  was  only  0.58  inch  less  than  that  of  the  same  period  in  1903-1904, 
no  widespread  damage  followed. 

The  seasons  with  highest  average  temperatures  for  the  last  of  the  grow- 
ing season,  1900  and  1906,  were  not  followed  by  the  greatest  destruction. 
The  lowest  monthly  temperatures  for  October,  November,  January  and 
February  came  in  years  not  distinguished  for  greatest  winter-killing. 
Only  in  December  did  the  lowest  monthly  temperature  occur  in  a  winter 
of  extensive  injury.  The  absolute  minima  for  October,  for  November 
and  for  January  fall  outside  the  years  of  greatest  damage. 

Reviewing  by  seasons:  the  1895-1896  winter  shows  extreme  condi- 
tions (heavy  type)  in  low  rainfall  and  low  late  winter  temperatures;  the 
most  noteworthy  divergence  of  the  1903-1904  winter  was  the  heavy 
rainfall,  while  for  1917-1918  the  high  and  low  monthly  precipitations 
combined  to  make  an  average  rainfall  and  the  noteworthy  features  for 
that  winter  were  the  low  temperatures  of  November  and  December.  Not 
far  from  Geneva,  at  Ithaca,  Bailey*  wrote  of  the  1895-1896  winter,  "the 
phenomenal  injury  wrought  by  last  winter  was  probably  not  wholly  the 
result  of  low  temperature.  The  drought  of  the  last  summer  and  fall  no 
doubt  augmented  the  injury."  In  reviewing  the  winter  of  1903-1904, 
for  states  east  of  the  Mississippi,  Stockman^**  stated  that  the  severity 
"was  not  due  to  occurrence  of  very  low  minimum  temperatures  but  to 
the  number  and  succession  of  days  whose  mean  temperatures  continued 
below  the  normal ...  At  only  two  stations  having  25  years  or  more  of 
records  was  the  record  of  lowest  temperatures  broken.  No  record  of 
minimum  temperatures  at  a  regular  Weather  Bureau  station  was  broken 
during  December  and  February." 

It  seems,  then,  that  an  extreme  of  any  one  feature  of  the  climate  is 
not  of  itself  likely  to  cause  widespread  injury,  but  that  injury  depends 
considerably  on  a  combination  of  accentuated,  rather  than  on  isolated 
extreme,  conditions.  Thus  1895-1896  may  be  described  as  in  many  ways 
a  characteristic  Dakota  winter  in  its  drying  out  effects;  in  1903-1904 


WINTER  INJURY  267 

late  maturity  with  late  cold  and  in  1917-1918  immaturity  and  early 
cold  are  the  distinguishing  features. 

Speculation  is  uncertain  but  in  this  case  rather  interesting.  It  can- 
not, of  course,  be  proved  but  it  seems  possible  that  had  the  rainfalls  of 
1895  and  1917  been  exchanged  the  damage  would  have  been  less  in  both 
cases;  or,  had  the  rainfall  of  1915  been  combined  with  the  August-October 
temperature  of  1900  and  the  November  minimum  of  1904,  how  great 
might  have  been  the  danger!  Out  of  the  35  seasons  covered  in  Table 
18,  only  six  have  no  notable  climatic  extreme  to  be  recorded. 

Winter  Injuries  Classified. — Winter-killing  of  hardy  fruits  in  temper- 
ate regions,  then,  may  depend  on:  (1)  a  lack  of  maturity  in  tissues,  (2) 
a  lack  of  ability  to  resist  winter  drought  conditions,  (3)  too  ready  response 
to  short  periods  of  warm  weather  in  the  winter.  These  are  listed 
here  in  the  probable  order  of  their  relative  importance  and  frequency, 
though  in  any  given  section  the  sequence  may  be  changed.  In  the 
Minnesota-Dakota  section,  for  example,  it  is  probable  that  winter  drought 
and  absolute  cold  are  more  frequently  the  causes  of  winter-killing;  in  the 
northeast  the  lack  of  maturity  of  tissues  is  probably  the  one  dominant 
factor,  while  farther  south  much  of  the  winter-killing  of  buds  is  the  result 
of  the  breaking  of  dormancy  by  unseasonable  warm  weather,  followed  by 
ordinary  cold. 

These  classes  can  be  recognized  in  many  cases  by  the  form  of  the  resul- 
tant injury,  though  sometimes  different  causes  appear  to  have  nearly 
identical  effects.  Crown  injury  and  crotch  injury  may  be  related 
with  some  certainty  to  lack  of  maturity.  Killing  back  of  branches  results 
from  the  same  factor,  but  may  be  regarded  also  as  a  sign  of  varietal  ten- 
derness or  it  may  be  caused  by  winter  drought.  Killing  of  apple  fruit 
buds  in  northern  sections  appears  to  be  a  result  of  absolute  cold,  but  with 
peaches  in  climates  such  as  that  of  Missouri  it  is  to  a  considerable  extent 
induced  by  ready  development  before  cold  weather  has  passed.  Winter 
sun-scald  is  a  localized  manifestation,  ordinarily,  of  a  late  winter  freezing. 
Trunk  splitting  is  frequently  associated  with  an  immature  condition  and 
at  times  with  a  sudden  and  considerable  drop  in  temperature. 

The  diversity  of  causes  and  multiplicity  of  effects  make  it  quite  evi- 
dent that  any  attempt  at  setting  definite  temperatures  as  injurious  or  fatal 
without  regard  to  other  conditions  is  futile.  Though  there  is  a  generally 
accepted  belief  that  —  14°F.  is  fatal  to  peach  fruit  buds,  they  have  been 
known  to  survive  —  20°F.  It  is  not  always  the  coldest  winter  that  does 
the  greatest  damage.  Much  depends  on  the  character  of  the  preceding 
autumn,  whether  it  induced  proper  "ripening"  of  the  wood  or  forced 
late  growth  and  on  the  period  at  which  the  cold  weather  occurred;  of 
course  much  depends  on  the  treatment  accorded  any  given  orchard  or 
tree  during  the  preceding  summer  and  autumn. 


268  FUNDAMENTALS  OF  FRUIT  PRODUCTION      ' 

INJURIES  ASSOCIATED  WITH  IMMATURITY 

Early  maturity  of  wood  is  of  paramount  importance  in  most  of  the 
northeastern  United  States  and  is  by  no  means  a  negligible  factor  outside 
that  region.  Most  of  the  injury  in  Washington  state  orchards  in  the 
disastrous  freeze  of  late  November,  1896,  can  be  attributed  clearly  to 
immaturity  rather  than  to  the  actual  temperature  (  — 12°F.)  attained. ^^ 
Any  region  with  a  comparatively  short  growing  season  and  with  fairly 
heavy  late  summer  and  autumnal  rainfall  is  subject  to  winter  killing 
because  of  immaturity.  Other  combinations  of  conditions  may  produce 
occasionally  the  same  susceptibility  in  regions  ordinarily  free  from  these 
dangers.  Thus  in  most  irrigated  sections  climatic  conditions  are  such 
that  injuries  of  this  type  are  not  to  be  expected;  however,  they  are  fre- 
quently brought  about  by  the  injudicious  use  of  irrigation  water  early 
enough  in  the  autumn  to  prolong  growth.  In  the  freeze  of  1896,  in 
Washington,  most  of  the  orchards  that  had  been  irrigated  in  late  summer 
suffered  more  than  others.  ^^  L^te  irrigation  should  be  very  late,  if 
immunity  to  this  form  of  injury  is  to  be  insured.  Furthermore,  it  should 
be  borne  in  mind  that  maturity  is  only  a  relative  term,  the  so-called 
"maturity"  of  the  Willamette  valley,  for  example,  being  quite  different 
from  the  "maturity"  of  Wisconsin.  Therefore,  a  given  temperature, 
common  in  Wisconsin  but  unusual  in  the  Willamette,  might  be  harmless 
in  the  one  location  but  very  injurious  in  the  other,  even  to  trees  of  the 
same  variety. 

Much  of  the  damage  from  winter  temperatures  in  England  and  in 
northern  France  and  Germany  is  evidently  associated  with  lack  of  ma- 
turity, since  particularly  cool  summers  followed  by  winters  of  moderate 
severity  have  frequently  proved  more  damaging  than  colder  winters  that 
followed  favorable  growing  seasons.  A  "cold  winter"  for  England 
would  be  considered  mild  in  the  northern  states  or  Canada;  in  England 
it  might  cause  considerable  damage  and  none  in  New  York  or  Michigan. 
The  prevalence  of  "frost  cankers"  as  the  chief  manifestation  of  winter 
injury  in  England  lends  weight  to  this  view. 

Affecting  More  or  Less  the  Entire  Plant. — Emerson^"  states:  "  Resist- 
ance to  cold  in  trees  is  due  often  almost  wholly  to  the  habit  of  early 
maturity  rather  than  to  constitutional  hardiness.  Black  walnut  trees 
at  the  Experiment  Station  (Nebraska),  grown  from  northern  seed,  by 
virtue  of  perfect  maturity,  passed  through  the  extremely  severe  winter  of 
1898-1899  without  apparent  injury  while  similiar  black  walnut  trees  from 
southern  seed,  owing  to  imperfect  maturity,  have  had  their  new  growth 
killed  back  from  a  few  inches  to  two  or  three  feet  for  the  past  six  years  and 
yet  notwithstanding  this  great  difference  in  resistance  to  cold  in  winter,  a 
comparatively  hght  freeze  late  in  the  spring  of  1903  killed  the  new  growth 
of  the  northern  trees  just  as  completely  as  it  did  that  of  the  southern  ones. 


WINTER  INJURY  269 

Northern  trees  are  constitutionally  no  hardier  than  southern  but  their 
superior  resistance  to  winter  cold  was  due  to  their  habit  of  ripening  their 
new  growth  perfectly  in  the  fall." 

Macoun''^  introduces  evidence  to  the  same  effect:  "From  the  writer's 
experience  with  over  3,000  species  and  varieties  of  trees  and  shrubs, 
exclusive  of  cultivated  fruits,  from  many  countries  and  climates,  which 
are  under  his  care  and  observation  at  the  Central  Experiment  Farm, 
Ottawa,  we  have  drawn  the  following  conclusions  regarding  the  hardiness 
of  trees:  A  tree  or  shrub  which  will  withstand  a  test  winter  at  Ottawa 
must  be  one  which  ripens  its  wood  early.  Trees  or  shrubs  which  are 
native  to  places  having  a  longer  or  much  longer  growing  season  than  at 
Ottawa  grow  larger  than  native  species  or  those  from  a  somewhat  similiar 
climate  to  the  native  species,  and  when  a  test  winter  comes  their  wood  is 
not  sufficiently  ripened,  or  winter-resistant,  and  they  are  more  or  less 
injured  or  perish.  .  .  .  Another  observation  regarding  tender  trees  has 
been  that  after  a  season  when  the  growth  has  been  strong  more  injury  is 
likely  to  occur  than  in  a  season  when  the  growth  is  short  .  .  .  the 
season  of  all  the  hardiest  varieties  [of  apples]  is  summer  or  autumn  .  .  . 
apples  which  mature  early  and  are  in  condition  for  eating  in  summer  and 
autumn  are  grown  on  trees  which  ripen  their  wood  early,  and,  on  the  other 
hand,  an  apple  which  is  not  ready  for  use  until  winter  is  usually  grown 
on  a  tree  which  does  not  ripen  its  wood  early." 

Attention  may  be  called  to  the  doubtful  wisdom  of  fall  planting  in 
northern  regions  of  trees  grown  far  to  the  south.  These  trees,  to  be 
shipped  in  time  for  planting  in  the  north,  must  be  dug  when  they  are 
still  quite  immature.  They  are,  if  planted  in  the  fall,  exposed  to  cold 
winter  temperatures  and  are  thus  doubly  at  a  disadvantage.  It  is  true, 
the  digging  may  in  itself  induce  a  degree  of  maturit}^  through  drying  out, 
but  hardly  as  much  as  would  be  attained  by  trees  grown  farther  north. 
The  wisdom  of  delaying  digging  as  long  as  possible  is  obvious. 

Tender  Plants  may  he  More  Resistant  than  Hardier  Plants. — A  tempera- 
ture of  15°F.  at  South  Haven,  Mich.,  on  Oct.  10,  1906,  uniformly 
killed  peach  trees  while  pecans,  in  the  same  orchards,  survived.  ^^*  Here 
is  undeniable  evidence  of  a  tender  species  being  more  hardy  at  that  time 
because  of  maturity  than  a  species  that  is  far  more  hardy  in  its  mature 
condition.  Similarly,  records  show  that  apple  trees  planted  2  and 
3  years  in  Wyoming  were  killed  by  a  temperature  of  12°F.  in  Septem- 
ber, when  they  were  still  in  full  leaf  ,^^  though  there  are  numerous  instances 
of  trees  surviving  approximately  equal  temperatures  without  material 
injury  when  they  were  partly  leaved  out  in  the  spring. 

The  Effect  of  Slimmer  Conditions  Favorable  for  Late  Growth. — During 
the  winter  of  1903-1904  in  Ohio,  though  the  chief  damage  was  to  trees  of 
low  vitality,  vigorous  trees  succumbed  in  numerous  cases.  These  were 
almost  invariably  in  "low,  moist,  rich  black  soil  favoring  extreme  growth 


270 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


of  soft,  poorly  matured  wood,  or  in  orchards  in  rich  soils,  receiving  late 
cultivation."^^  Emerson^^  found  similar  susceptibility  in  peaches  grow- 
ing in  rather  moist  soils  or  receiving  late  cultivation  in  Nebraska.  Zero 
weather  or  even  6°F.  above  is  considered  more  harmful  in  very  early 
winter  in  Montana  than  -30°F.  or  -40°F.  later.e^ 

Selby^^^  supplies  other  interesting  cases  of  injury  in  Ohio  associated 
with  immaturity.  In  1880-1881,  late  cultivation  in  two  orchards, 
accompanied  by  heavy  August  rainfall  and  normal  September  rainfall, 
produced  heavy  and  prolonged  growth.  Late  November  brought  zero 
weather;  the  December  minimum  was  -13°F.  These  temperatures 
ordinarily  are  of  no  great  significance  but  in  this  case  they  caused  complete 
destruction  of  Baldwin  apple  trees.  On  a  larger  scale  and  over  a  wider 
area,  the  same  climatic  conditions,  when  approximated  in  the  growing  sea- 
son of  1906,  were  followed  by  widespread  winter  injury.  In  this  case  the 
following  winter  was  severe  but,  as  is  shown  in  Table  19,  arranged  from 
Selby's  data,  in  no  month  of  this  winter  did  the  temperature  closely 
approach  recorded  minima.  It  was  definitely  established  that  much  of 
the  injury  was  done  by  a  temperature  of  +  18°F.  on  Oct.  12.  The 
unusual  features  of  these  two  damaging  years  were,  not  the  winter 
temperatures,    but    the    summer   and   fall   temperatures   and    rainfall. 


Table  19. — Climatic  Conditions  Accompanying  W 

INTER 

Injury  in  Ohio^" 

Temperature  (degrees.  Fahrenheit) 

R 

linfall  (inches) 

Month 

1880              Average  23 
years 

1906 

1880 

Average 
23    years 

1906 

Mean 

^^"'-     Mean 
mum 

Mini- 
mum 

Mean 

Mini- 
mum 

May 

65.8 
63.4 
74.5 
71.0 
64.8 
52.3 
33.9 
25.7 

35.5    61.2 
45.5    69.7 
52.0    73.9 
48.0    71.5 
41.5    65.5 
30.5    53.5 
-5.0    40.9 

19 
29 
34 
31 
23 
8 
-8 
-32 

61.3 
69.8 
72.1 
74.6 
68.9 
52.7 
41.  1 
32.3 

24 
34 
43 
43 
36 
18 
14 
-15 

1.24 
5.65 
6.06 
5.03 
2.02 
2.27 
2.39 
1.06 

3.63 
3.94 
3.37 
3.04 
2.71 
2.13 
3.05 
2.74 

2   17 

July 

August             

4   77 

September 

2  92 

October 

3   19 

1881          1 

1907 

1881 

1907 

January 

24.2 
29.0 
35.6 

-2.0    27.8 
-2.5    26.8 
13.0    38.8 

-34 
-39 

-17 

32.2 
26.0 
45.9 

-23 
-19 

-2 

1.31 
3.25 

2.75 

2.70 
2.66 
3.39 

6.11 
0  85 

March 

5.55 

"Second  Growth"  Particularly  Susceptible. — Excessively  dry  summer 
weather  also,  if  followed  by  a  fair  precipitation  in  early  autumn,  may 
result  in  immature  wood  at  the  entrance  into  winter. ^^^  The  dry  sum- 
mer may  cause  a  "premature  dormancy"  followed  by  second  growth. 


WINTER  INJURY  271 

Instances  of  this  are  furnished  sometimes  by  the  fall  blossoming  of  fruit 
trees.  The  severe  winter  of  1917-1918  resulted  in  greater  damage  to  old 
trees  in  Indiana  than  to  young  and  the  suggestion  is  made  that  this  con- 
dition "is  possibly  accounted  for  by  the  fact  that  many  old  trees  made  a 
late  second  growth  while  on  vigorous  young  trees  the  growth  was  not 
arrested  by  dry  weather  in  late  summer  and  they  matured  normally.  "^^ 
It  is  interesting  to  contrast  this  condition  with  the  greater  damage  to 
young  trees  in  Ohio  following  the  wet  summer  of  1906. 

Preventive  Measures. — Unfortunately  the  weather  cannot  be  predicted 
reliably  far  ahead.  However,  it  seems  evident  that  August  rainfall 
frequently  is  important  in  the  northeast  in  determining  tree  maturity 
in  October  and  that  orchard  operations  in  that  section  should  be  varied 
somewhat  during  August  according  to  the  rainfall.  A  very  dry  August 
should  be  accompanied  by  late  cultivation  to  lessen  the  likelihood  of 
second  growth;  a  very  wet  August  would  indicate  the  wisdom  of  stopping 
cultivat;ion  altogether  and  sowing  a  quick-growing,  moisture-consuming 
cover  crop.  A  warm,  moist  October -cannot  be  foretold  but  its  effects 
can  be  forestalled,  at  least  in  part,  by  a  suitable  cover  crop  which  will 
reduce  soil  moisture. 

Localized  Injuries. — Aside  from  the  occasional  serious  and  widespread 
damages  just  mentioned,  there  are,  probably  every  winter,  minor  localized 
injuries.  It  is  impossible,  however,  to  draw  any  sharp  line  between 
what  is  here  termed  localized  injuries  and  more  general  injury.  For 
instance,  the  killing  back  of  shoots,  canes  or  limbs,  if  severe,  would  be 
considered  in  the  latter  class;  if  it  were  light  it  might  as  readily  be  con- 
sidered localized. 

Crotch  and  Crown  Injury. — A  form  of  injury,  often  unnoticed  for 
some  time  after  its  occurrence,  but  with  greater  potentiality  of  ulti- 
mate serious  consequences,  is  the  killing  of  more  or  less  limited  areas 
of  bark  on  the  trunk,  particularly  at  the  crown  of  the  tree  or  at  the 
crotches.  Attention  may  be  drawn  to  the  dead  area  first  by  its  sunken 
appearance  consequent  to  the  growth  of  the  surrounding  uninjured  tissue 
or  it  may  become  evident  through  the  cracking  of  the  bark  at  the  injured 
area  or  sometimes  by  the  loosening  of  the  bark. 

Of  the  apple  varieties  commonly  grown  in  the  regions  where  this 
injury  has  been  most  studied,  Ben  Davis  seems  most  susceptible,  with 
Baldwin  showing  considerable  tenderness  in  this  respect.  King,  though 
less  widely  grown,  is  so  notoriously  subject  to  this  malady  that  the  injury 
is  sometimes  called  the  "King  disease."  It  seems  significant  that  all 
of  these  varieties  are  late  growers.  Gravenstein,  in  Nova  Scotia,  is 
also  reported  as  susceptible. ^^^ 

Grossenbacher'*2  i-epoi-ts  crown  rot  much  more  common  in  cultivated 
land  than  in  sod  and  particularly  in  land  formerly  in  sod  but  recently 
plowed.     He  also  reports  high,  wind-swept  situations  with  thin  soils  to 


272  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

be  more  subject,  though  it  seemingly  appears  in  any  situation.  No 
one  side  of  the  trees  is  uniformly  injured,  according  to  his  observations, 
though  all  cases  occurring  at  any  one  time  in  a  given  orchard  are  likely 
to  be  confined  to  some  particular  exposure.  Trees  which  have  made  a 
rather  unusually  large,  or  rather  late,  growth  appear  more  liable  to 
injury. 

In  the  1913  freeze,  in  the  citrus  regions  of  California,  the  crotches 
were  the  parts  of  the  trunk  found  most  damaged. -"''  Crotch  injury 
and  those  forms  of  crown  rot  not  due  primarily  to  the  attacks  of  parasitic 
organisms  are  probably  most  frequently  associated  with  early  winter 
injuries  associated  with  immaturity.  Consequent  to  the  winter  injury, 
fungus  infestation  of  the  dead  area  may  appear  but,  excepting  the  fire- 
blight  bacillus,  no  organism  has  been  shown  definitely  to  be  the  primary 
causative  agent  in  producing  this  disorder. 

Localized  Injuries  and  Delayed  Maturity. — Chandler^^  states:  "The 
wood  at  the  base  of  the  trunk  and  at  the  crotches  of  all  rapidly^  growing 
branches  seems  to  reach  a  condition  of  maturity  in  early  winter  more 
slowly  than  does  other  tissue. " 

This  view  corroborates  studies  by  Mer^^^  on  the  duration  of  cambial 
activity  in  various  trees,  reported  in  part  as  follows.  "Just  as  it  awakes 
gradually  in  the  different  regions  of  a  tree  cambial  activity  ceases  pro- 
gressively at  the  end  of  summer.  ...  It  disappears  from  the  branches 
before  disappearing  from  the  trunk.  In  trees  that  are  closely  grouped,  it 
leaves  first  the  low  branches,  less  vigorous  than  those  of  the  top,  and  the 
basal  and  median  parts  of  these  branches  before  their  extremity.  It  is 
only  following  this  that  it  leaves  the  higher  shoots.  In  the  large  branches 
of  an  isolated  tree  it  stops  earlier  at  the  tips  than  at  the  middle.  It  is  at 
the  level  of  the  basal  swelling  that  it  persists  the  longest.  In  the  trunk 
it  stops  first  at  the  top,  then  at  the  middle  and  finally  at  the  base.  When 
growth  is  not  very  active  it  ceases,  on  the  contrary,  earlier  in  the  lower 
region.  ...  It  is  in  the  portion  of  the  trunk  situated  immediately 
below  the  soil  that  cambial  activity  is  confined  last. 

"It  is  evident  that  in  the  regions  of  the  trunk  where  the  vegetative 
activity  is  the  most  pronounced,  because  they  are  the  youngest  or 
because  they  are  the  best  nourished,  that  cambial  activity  awakes 
first.  .  .  .  It  is  there  also,  that  in  general,  it  stops  latest.  On  the  other 
hand,  in  all  circumstances  where  growth  is  slow,  we  see  cambial  activity 
manifesting  itself  slowly  and  stopping  earlier.  .  .  .  Between  the  length 
of  the  cambial  activity  and  its  intensity  there  is,  then,  a  manifest 
relation." 

This  statement  seems  in  itself  adequate  explanation  for  much  of  the 
localization  of  winter  injury  associated  with  immaturity.  Field  studies 
in  several  regions  seem  to  correlate  immaturity  with  this  type  of  injury 
rather  uniformly. 


WINTER  INJURY 


273 


Contributing  Factors. — The  drying  effect,  of  wind  should  be  considered, 
as  also  the  effect  of  cold  winds  on  the  temperature  of  the  exposed  tissues. 
Winter  killing  is  sometimes  more  severe  in  the  three  or  four  rows  nearest 
the  windward  side  of  the  orchard.  Many  of  the  older  prune  orchards  in 
the  northern  end  of  the  Willamette  valley  still  showed,  15  years  later, 
the  marks  of  the  freeze  of  November,  1896,  in  the  shape  of  dead  areas  on 
the  northwest  sides  of  the  trunks,  corresponding  to  the  direction  of  the  air 
drift  at  the  time  of  the  freeze.  In  many  cases  of  this  sort  the  dead  tissue 
ceases  abruptly  at  the  point  where  snow  stood  at  the  time  of  the  injury, 
suggesting  at  least  that  the  injury  was  due  to  the  temperature  effect  of 
the  wind.  The  effect  of  snow  on  soil  temperatures  will  be  shown 
later.  This  protective  influence  evidently  is  not  confined  to  the  soil, 
as  data  shown  in  Table  20  clearly  indicate. 


Table  20. 


Temperature  Under  10-Centimeter  Snow  Covering 
{After  Goeppert^^^) 


Date 

Under  snow, 
degrees  Centigrade 

Air, 
degrees  Centigrade 

Feb.    4         

-3.0 
-4.6 
-6.5 
-6.0 
-5.0 
-2.0 
-15 

-12.6 

Feb.    5 

-14.7 

Feb.    8 

-16.7 

Feb.  10 

-14.9 

Feb   11                                                

-15.8 

Feb.  13                 

-  5.7 

Feb.  15 

-  2.8 

Consideration  should  be  given,  also,  to  the  unequal  maturing  of 
tissues  on  different  sides  of  the  tree  trunk.  Casual  observations  in 
autumn  have  indicated  that  maturity  may  be  attained  more  rapidly  on 
one  side  of  the  stem  than  on  another.  It  would  follow,  then,  that  a  given 
temperature  in  autumn  might  prove  injurious  to  the  tissues  of  one  side 
and  not  of  the  other,  without  the  intervention  of  other  causal  agents. 
Furthermore,  it  should  be  considered  that  the  temperature  a  few  inches 
above  the  soil  may  be,  on  clear  cold  fall  nights,  10°  colder  than  is  indicated 
by  a  shelter  thermometer,  so  that  an  official  temperature  record  of  20°F. 
may  mean  that  the  tissues  at  the  crown  were  exposed  to  a  temperature 
of  10°F. 

Remedial  Measures. — In  view  of  the  different  circumstances  under 
which  this  type  of  injury  occurs  it  is  probable  that  not  all  the  factors 
mentioned  are  operative  in  any  given  instance  and  that  only  one  of  them, 
if  sufficiently  intensified,  may  produce  the  injury.  The  one  condition 
apparently  requisite  to  crown  rot  and  to  crotch  injury  is  immaturity 
in  the  tissues  at  the  point  involved.     The  prospective  grower  is  safe  in 

18 


274  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

utilizing  protection,  natural  or  created,  from  winds,  particularly  those 
prevailing  in  early  winter,  and  the  grower  whose  orchard  is  on  an  exposed 
site  should  pay  careful  attention  to  the  attainment  of  as  complete 
maturity  as  possible  in  his  trees.  Banking,  though  laborious  and 
expensive,  is  justified  under  threatening  conditions.  For  trees  already 
damaged  the  best  treatment  is  to  cut  away  the  injured  bark  and  to  cover 
the  exposed  surfaces  with  grafting  wax  or  paint  and  possibly  to 
bridge-graft. 

WINTER  INJURY   ASSOCIATED   WITH   DROUGHT 

In  spite  of  the  great  water-retaining  capacity  of  the  tissues  of  the 
most  hardy  deciduous  fruits  in  a  dormant  state,  they  are  not  able  to 
withstand  an  indefinite  amount  of  desiccation.  Especially  when  the 
evaporating  power  of  the  air  is  high  they  gradually  lose  water.  This  will 
result  eventually  in  a  desiccation  that  may  mean  the  death  of  the  tissue 
unless  the  water  lost  is  replaced  promptly.  Recovery  from  winter 
desiccation,  or  the  ability  to  withstand  long  continued  hard  freezing 
(physiological  drought)  or  long  continued  winter  drought  (atmospheric), 
depends  therefore  on  a  supply  of  available  moisture  upon  which  the 
roots  may  draw.  In  many  sections  there  is  seldom,  if  ever,  a  winter 
when  soil  moisture  would  be  a  limiting  factor  in  this  connection.  In 
others  it  is  frequently  a  limiting  factor  and  gives  rise  to  those  injuries  that 
are  classed  here  as  associated  with  winter  drought. 

Fundamentally  all  injury  to  dormant  tissues  from  cold  is  to  be  regarded  as 
induced  by  drying  out.  Paradoxically,  it  is  generally  the  tissue  containing  the 
most  moisture  that  is  most  subject  to  damage.  The  injury,  however,  comes  from 
immaturity  and  not  from  excess  moisture.  Apparently  there  is  a  certain  quan- 
tum of  water,  varying  with  the  kind  of  plant  and  with  conditions,  that  is  essential 
to  protoplasmic  life  and  this  is  retained  more  tenaciously  by  mature  tissue. 
Hence,  in  considering  winter  injury  a  distinction  must  be  drawn  between  mois- 
ture in  the  plant  tissues  (water  of  composition  and  surplus  moisture)  and 
moisture  in  the  environment.  Though  the  two  are  closely  related,  freezing 
(drying  out)  of  immature  tissue  in  a  moist  environment  should  be  distinguished 
from  freezing  (drying  out)  due  to  dry  environment  though  the  final  lethal 
process  is  the  same. 

Immaturity  and  Winter  Drought 

Injury  from  drying  out  may  have  certain  manifestations  in  agreement 
with  that  from  immaturity.  It  is,  however,  somewhat  more  evident 
in  the  tops  though  it  may  extend  to  the  trunk.  Fruit  buds  in  the  apple 
are  killed  more  generally  by  this  type  of  freezing  than  through  imma- 
turity. Wood  formed  the  previous  year  suffers  heavily;  with  more 
extreme  conditions  the  damage  extends  downward.  Injury  associated 
with  immaturity  may  start  either  on  the  young  twigs  or  on  the  trunk. 


WINTER  INJURY 


275 


In  one  case  the  young  twigs  suffer  because  they  are  immature;  in  the 
other  because  they  are  the  most  subject  to  drying  out,  just  as  they  would 
be  in  excessive  growing  season  drought.  Winter  drought  injury  may 
discolor  wood  on  older  parts  of  the  tree  but  it  does  not  kill  cambium 
readily. 

It  should  be  remarked,  also,  that  in  some  regions  it  is  quite  conceiv- 
able that  nmch  of  the  winter  killing  in  the  tops  may  originate  primarily 
as  root  killing.  Conditions  there  are  favorable  to  root  injury  and  it  has 
been  definitely  shown  many  times  to  occur.  Early  winter  root  killing 
would  be  followed  by  a  drying  out  of  the  top.  The  latter  symptom  natu- 
rally would  be  more  evident  and  would  pass  as  killing  of  the  top,  the 
true  cause  being  obscured.  However,  the  preventives  for  both  classes  of 
injury  agree  in  requiring  a  high  soil  moisture  content  after  danger  of 
inducing  late  growth  has  passed. 

Water  Loss  from  Dormant  Tissues 

Some  measure  of  the  loss  of  water  by  dormant  trees  is  afforded  by  the 
data  presented  in  Table  21  showing  decreases  in  weight  of  8-year  old 
apple  trees  during  two  winters  in  Wisconsin.!''^  Obviously  these  losses 
are  in  trees  severed  from  their  roots.  If  the  loss  in  moisture  of  standing 
trees,  where  the  supply  of  water  would  be  renewed  to  some  extent,  should 
be  determined,  it  would  be  considerably  greater  but  the  degree  of  exhaus- 
tion would  be  less  because,  as  has  been  shown  earlier,  the  loss  by  evapora- 
tion diminishes  as  the  degree  of  exhaustion  increases.  If  the  dry  weight 
of  the  trees  could  be  deducted,  the  percentage  loss  of  moisture  would  be 
correspondingly  increased.  Quite  noticeable  are  the  differences  in 
moisture  losses  during  the  two  winters  recorded  in  Table  21.  The  winter 
of  1903-1904,  though  severe,  was  moist  and  many  cloudy  days  occurred. 
There  was  little  winter  injury  in  Wisconsin  during  that  season. 


Table  21. 


-Loss  IN  Weight  of  Apple  Trees  During  Two  Winters'^* 
(Weight,  pounds) 


Dute 

Tree  1 

Tree  2 

Tree  3 

Tree  4 

Dec.   19,  1902 

36.6 

24.6 

35.7 

30.4 

Feb.   27.  1903 

34.7 

23.5 

34.4 

29.0 

Apr.     3,1903 

31.4 

21.4 

31.6 

26.5 

Loss 

5.2 

5.2 

4.1 

3  9 

Dec.     5,1903 

26.2 

24.2 

Mar.  26,  1904              

25.6 

23.6 

Loss 

0  6 

0,6 

276  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Bailey^"^  estimates  that  a  large  apple  tree  loses  from  250  to  350  grams 
of  water  each  day  through  the  winter.  Observations  on  moisture  content 
of  apple  twigs  in  Iowa  show  an  actual  increase  from  November  to  Decem- 
ber in  many  varieties;  on  Jan.  15,  however,  following  several  days  of 
severe  cold,  there  was  a  very  marked  decrease,  though  the  respective 
intervals  between  observations  were  5  weeks  and  3  weeks^*^  (see  Table  13). 

Water  Conduction  in  Trees  During  the  Winter 

Bailey  ^°  cites  evidence  gathered  in  New  York  showing  loss  of  moisture 
in  twigs  during  winter  and  a  higher  moisture  content  during  a  thaw  than 
during  a  previous  period  of  cold  weather,  indicating  a  conduction  of  sap 
during  the  milder  weather.  Indeed  such  a  conduction  must  be  conceded 
else  the  tree  would  inevitably  dry  out.  Wiegand^i"*  showed  a  conduction 
of  water  to  Pinus  Laricio  buds  at  temperatures  between  —  18°C.  and 
—  6.7°C.  Buds  severed  from  the  tree  but  sealed  immediately  on  the 
cut  surfaces  showed  an  average  water  content  of  41.2  per  cent,  after  3 
days  while  buds  taken  fresh  from  the  tree  at  the  end  of  this  time,  even 
though  the  twigs  had  been  frozen,  showed  an  average  content  of  47.5 
per  cent.  It  is  probable  that  interference  with  conduction,  or  an  evapora- 
tion rate  much  higher  than  conduction,  is  just  the  condition  requisite  for 
winter  drought  injury. 

Relation  of  Freezing  to  Water  Conduction. — It  is  well  known  to  every 
wood-chopper  of  the  northern  woods  that  trees  freeze  even  to  the  center 
in  prolonged  cold  weather.  Investigations  have  shown  that  in  trees  of  6 
to  8  inches  diameter  the  difference  in  temperature  between  the  center  and 
the  outside  in  the  morning  is  only  1  °  or  2°R. ,  though  in  trees  2  feet  in  diam- 
eter it  may  be  on  single  days  5°,  6°  or  7°Il. ;  with  air  temperatures  of  — 13° 
to  —  15°R.  the  tree  temperature  was  —12°  to  —  14°R.;  most  important, 
the  longer  the  temperature  of  the  air  remains  uniform  the  more  the  tem- 
perature of  the  tree  approaches  that  of  the  air.^^^  The  temperature  of  the 
alburnum  or  sap  wood  in  maple  has  been  shown  to  follow  the  air  tempera- 
tures fairly  closely.  ^^^'^  More  detailed  figures  taken  morning,  noon  and 
night,  at  a  depth  of  8  centimeters  in  a  box  elder  tree,  indicate  that  tree 
temperatures  follow  the  trend  of  the  air  temperatures  very  closely,  not, 
however,  reaching  the  full  extremes  of  the  outside  fluctuations  unless 
these  are  maintained  for  some  time.'^^  Figure  27,  arranged  from  a  part 
of  these  figures,  shows  typical  daily  fluctuations  of  air  and  tree  tempera- 
tures. Table  22  shows  the  averages  of  the  temperatures  recorded  during 
January  and  February.  Observations  in  Lapland  show  winter  tempera- 
tures in  live  and  dead  trees  to  be  practically  the  same."^ 

Grape  vines  have  been  grown  in  a  greenhouse,  so  trained  that  certain 
canes  passed  outside  and  were  then  brought  back  into  the  house.  The 
base  and  the  upper  parts,  inside  the  greenhouse,  opened  their  buds 
quickly  and  continued  to  grow.     On  cold  mornings,  however,  with  the 


WINTER  INJURY 


277 


outside  temperature  around  —  10°C.,  the  leaves  on  the  upper  part  of 
the  stem  were  very  much  wilted,  because  of  the  interference  with  sap 
conduction  in  the  portion  of  the  stem  outside.  With  rising  temperature, 
however,  they  recovered. ^^ 


10         II         12         13        14-        15        16 
February 

Fig.  27. — Temperature  fluctuations  in  a  tree  trunk.     (After  Squires^^) 


Table  22. — Tree  and  Air  Temperatures 

(After  Squires''-^^) 


Januarv 


February 


Air,  degrees 
Centigrade 


Tree,  degrees 
Centigrade 


Air,  degrees 
Centigrade 


Tree,  degrees 
Centigrade 


6  to  7  a.m 
12  to  1  p.m 

6  to  7  p.m 
En  tiro  dav 


10.84 
6.60 
9.20 

s.ss 


-9.37 
-8.90 
-7.50 


11.93 
4.35 
8.65 
8.31 


-10.46 
-7.55 

-  7.00 

-  8.34 


These  considerations  make  it  evident  that  prolonged  cold  weather 
must  interfere  materially  with  sap  conduction  while  at  the  same  time  the 
conditions  accompanying  extreme  cold  are  the  very  conditions  which 
favor  greater  drjnng  out.  It  should  be  considered,  too,  that  the  conduc- 
tive regions  in  the  tree  are  near  the  outside  of  the  stem.  Many  cases  of 
twig  killing  must,  therefore,  be  considered  as  due  to  drought,  short, 
perhaps,  but  intense  in  localized  areas.  Possibly  the  greater  suscepti- 
bility of  twigs  to  this  injury  is  not  due  entirely  to  failure  in  conduction 


278  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

but  may  be  explained  in  part  by  the  lack  of  a  sufficient  amount  of  sap- 
wood  to  serve  as  a  local  reservoir.  Even  prolonged  cold  does  not  affect 
the  upper  part  of  tall  trunks  as  much  as  it  does  the  low,  smaller  branches 
though  conduction  from  the  ground  is  conceivably  as  difficult;  the  tissues 
on  the  trunk,  however,  have  both  relatively  and  absolutely  a  greater 
amount  of  sapwood  on  which  presumably  they  may  draw. 

Where  Winter  Drought  Conditions  Prevail 

Winter  drought  conditions  are  in  a  measure  independent  of  soil  con- 
ditions and  can  be  considered  as  of  possible  occurrence  over  a  wide  range 
of  territory.  The  coldest  weather  in  humid  sections  is  accompanied  by 
dry  atmospheric  conditions;  occasionally  after  a  dry  summer  and  fall 
these  sections  suffer  from  winter  killing  due  to  desiccation.  Long  con- 
tinued severe,  though  not  excessive,  cold  would  induce  physiological 
drought.  The  winter  of  1895,  already  mentioned,  was  of  this  type.  It 
is,  however,  infinitely  more  common,  in  proportion  to  the  amount  of 
fruit  grown,  in  regions  of  prevailingly  dry  atmosphere  and  intense  cold. 
Wyoming,  the  Dakotas  and  parts  of  Minnesota  furnish  abundant 
examples.  Rainfall  is  comparatively  light  in  those  sections  and  the  soil 
frequently  freezes  with  a  low  moisture  content.  Winter  precipitation  is 
less  than  summer,  frequently  only  a  fourth  as  great  and  there  is  much 
clear,  cold  weather. 

Protection  Against  Winter  Drought  Injuries 

Necessarily  protective  measures  against  winter  injury  associated  with 
drought  must  be  preventive.  They  must  either  reduce  water  loss  or 
increase  water  supply. 

Winter  Irrigation. — Buffum^^  advocates  in  Wyoming  thorough  irriga- 
tion "late  in  the  fall,  before  the  ground  has  frozen  and  when  growth 
has  ceased.  The  later  this  irrigation  can  be  done  the  better  as  the 
object  is  to  store  moisture  in  the  soil  sufficient  for  winter  .  .  .where 
orchards  are  planted  on  bottom  lands  that  have  a  continual  supply  of 
moisture  fall  irrigation  may  be  unnecessary.  But  on  upland  it  is  the 
surest  way  to  prevent  trees  from  winter  killing  and  when  possible  irri- 
gations through  the  winter  will  be  found  advantageous. "  In  North 
Dakota,  Waldron^^^  writes:  "Parts  of  our  own  plantation  have  been 
cultivated  every  year  until  the  ground  freezes  with  only  the  best  results 
.  ,  .  the  treatment  that  provides  the  trees  with  the  greatest  amount 
of  soU  moisture  in  the  fall  will  tend  to  prevent  winter  kUling."  Else- 
where the  same  writer  states:  "The  cause  of  winter  killing  in  mild 
weather  is  the  drying  up  of  the  twigs ....  Trees  and  shrubs  that  are 
neglected  during  the  latter  part  of  summer  so  that  the  ground  becomes 
hard  and  dry,  ripen  their  wood  prematurely  and  unless  fall  rains  are 
abundant  the  drying  process  sets  in  before  winter  begins,  leaving  the 


WINTER  INJURY 


279 


plant  in  poor  shape  to  endure  further  drying.  .  .  .  Some  of  the  plants 
that  defer  this  change  (to  winter  condition)  the  longest  are  among  the 
hardiest  we  have.''^*'*' 

Cultivation. — Experimental  demonstrations  with  Wealthy  apple  trees, 
on    15    widely   separated    farms   in    South    Dakota,    give  quantitative 


Table  23. — Effect  of   Cultuhal   Conditions 

Dakota^-s 


ON  Winter   Killing   in  South 


Lot 
number 

Number 
trees, 
1916 

Number 

trees  dead, 

1919 

Number 

trees 

severely 

injured, 

1919 

Number 

healthy 

trees,   1919 

Average 
growth 

(inches,) 

Average  per- 
centage  of 
soil  moisture, 
Nov.  15 

Average  per- 
centage  of 
soil  moisture, 
Feb.  15 

1 

2 
3 
4 

50 
50 
50 
50 

41 
16 

22 

7 

7 
18 

13 

11 

2 
16 
13 

32 

2.0 
9.0 
6.5 
15.0 

14.70 
17.95 
15.50 
31.50 

14.2 
19.2 

15.2 
33.8 

verification  of  the  opinions  just  quoted  (Table  23).  Lot  1,  showing  the 
lowest  moisture  content  and  the  greatest  injury  to  trees,  was  composed  of 
trees  planted  in  prairie  sod;  Lot  2  was  cultivated  each  10  days  till  Aug. 
10;  Lot  3  was  "cultivated  each  10  days  till  July  1,  followed  by  a  cover 
crop  of  fall  rye  or  buckwheat"  and  Lot  4,  which  showed  least  injury, 
was  cultivated  each  10  days  until  Aug.  10,  just  as  Lot  2,  but  in  addition 
received  a  heavy  watering  just  before  the  ground  froze  for  the  winter. 
The  investigator  concluded  that  "summer  cultivation  is  positivelj^ needed 
and  in  very  dry  seasons  fall  watering  or  irrigation  of  some  sort  is  not 
only  advantageous  but  necessary." 

Cover  Crops.— Another  point  of  interest  here  is  the  lower  soil  moisture 
in  the  cover  crop  lot  and  the  somewhat  greater  attendant  injury,  as 
compared  with  the  clean  cultivated  lot.  Had  a  winter  favorable  to 
root  killing  intervened,  the  results  in  these  two  plots  might  have  been 
different.  However,  the  danger  from  cover  crops  in  this  region  of  light 
rainfall  is  apparently  more  frequently  present  than  the  danger  from  their 
absence  which  is  discussed  presently.  This  point  doubtless  has  occasion- 
ally equal  application  in  dry  situations  in  other  regions.  Comparison  of 
these  results  with  those  of  Emerson,  reported  below,  indicate  that  the 
best  insurance  against  winter  injury  in  general  in  this  region — and  in 
occasional  sites  in  more  humid  sections — is  a  frost-tender  cover  crop 
with  a  heavy  late  fall  irrigation.  To  be  sure,  in  those  districts  where 
irrigation  water  is  not  available,  the  preventive  measures  against  the 
winter  injuries  associated  with  drought  must  of  necessity  be  incomplete. 
However,  the  recognition  of  the  liability  of  a  given  site  to  this  form  of 
injury  may  enable  the  grower  so  to  shape  his  cultural  practices  early  in 
the  season  as  to  minimize  the  danger. 


280 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Studies  by  Emerson''^  in  Nebraska  show  the  effect  of  cover  crops  of 
different  kinds  on  the  hardiness  of  young  peach  trees.  The  cover  crops 
are  considered  in  two  classes,  frost-resistant  and  frost-killed.  Table  24, 
reproduced  from  Emerson's  report,  shows  the  effect  of  these  crops  on  soil 
moisture  content. 


Table  24. — Effect  of  Various  Cover  Crops  on  Soil  Moisture  During  the  Fall 

OF  1900^^ 


Kind  of  cover  crop 

Sept.  20 

Oct.  9 

Oct.  27 

Nov.  7 

Nov.  20 

Dec.  11 

Frost-resistant  crops: 
Rye 

15.2 
15.1 
15.8 
19.5 

16.4 

16.5 
17.3 
17.6 

17.1 

20.0 
18.6 

19.3 

11.8 
13.3 
12.8 
15.8 

13.4 

12.6 
15.1 
13.8 

13.8 

18.4 
17.8 

18.1 

12.1 
12.3 
11.8 
14.7 

12.7 

12.4 
13,8 
13.5 

13.2 

20.3 

18.2 

19.3 

14.1 
14.9 
14.4 
17.2 

15.2 

19.4 
20.0 

18.7 

19.4 

20.6 
19.1 

19.9 

15.5 
13.9 
14.2 
15.0 

14.7 

18.9 
19.6 
19.0 

19.2 

19.8 
18.3 

19.1 

16.0 

Oats 

14.4 

Rape 

14.0 

Field  peas 

Average 

Frost-killed  crops: 

Millet 

15.6 
15.0 
17.6 

Cane 

Corn 

17.9 
19.7 

18.4 

No  crop: 
Few  weeds 

18.1 

Few  weeds            

18.5 

Average 

18.3 

Figure  28,  also  from  Emerson,  a  graphic  representation  of  the  same 
figures,  shows  these  effects  even  more  strikingly.     Both  classes  reduced 


7     20       II 
NOV.        DEC. 

Fig.  28. — Percentages  of  soil  moisture  in  bare  ground  and  under  frost-killed  and  frost- 
resistant  cover  crops.      (After  Emerson^^) 

soil  moisture  sharply  in  September  and  October,  a  very  desirable  effect 
when  the  need  for  ripening  of  wood  is  considered.     Early  in  November, 


WINTER  INJURY  281 

however,  the  frost-killed  crops,  no  longer  growing,  ceased  to  draw  on  the 
moisture  supply  while  the  frost-resistant  crops  kept  the  moisture  content 
low.  When  it  is  recalled  that  Emerson's  earlier  work  showed  19  dead 
trees  and  none  uninjured  out  of  25  in  soil  with  15.2  per  cent,  moisture,  as 
here  under  frost-resistant  crops,  while  soil  with  19.8  per  cent.,  the  nearest 
figure  to  that  of  the  soil  under  frost-killed  crops,  showed  three  dead  and 
12  uninjured,  the  importance  of  this  difference  is  evident.  The  graph 
for  the  soil  with  no  cover  crop  shows  a  somewhat  higher  moisture  content 
in  December  than  either  class  of  cover  crops  but  it  also  shows  a  high 
moisture  content  in  September  and  October,  suggesting  a  prolonged 
growing  season  and  poor  maturity  in  the  tops.  This  is  what  actually 
occurred.  Emerson's  work  emphasizes  the  importance  of  a  water  supply 
after  maturity  is  attained. 

A  plentiful  supply  of  available  water  is  an  important  factor  deter- 
mining the  recovery  of  plant  tissues  from  the  effects  of  low  temperatures. 
Pantanelli  has  shown  that  the  activity  of  the  roots  is  of  great  importance 
in  determining  the  recuperative  power  of  the  plant  after  the  aerial  parts 
have  been  exposed  to  low  temperatures  and  that  all  those  factors  that 
reduce  the  absorbing  capacity  of  the  roots,  such  as  insufficient  aeration, 
salinity,  alkalinity  and  the  presence  of  toxic  substances  reduce  the 
recuperative  power  of  the  plant. 

Windbreaks. — The  relation  to  the  orchard  of  shelter  belts  composed  of 
hardy  trees  and  shrubs  has  been  the  subject  of  much  discussion,  of  some 
observation  but  of  little  precise  study.  Variations  in  local  conditions 
of  exposure  to  prevailing  winds  and  in  the  character  of  these  prevailing 
winds,  as  well  as  the  topography  of  the  orchards  themselves,  pre- 
clude the  possibility  of  windbreaks  being  universally  beneficial  or  injurious. 
Their  efficacy,  when  properly  placed,  in  cutting  down  the  windfall 
loss  from  summer  storms,  is  not  a  matter  for  discussion  here.  In 
the  Michigan  and  New  York  fruit  sections  much  of  the  advantage 
claimed  for  them  is  the  protection  they  afford  from  those  types  of 
winter  injury  that  are  associated  with  drying  out  and  they  are  set  usually 
on  a  northern  boundary  of  the  orchard.  In  the  north  central  states 
windbreaks  seem  to  be  planted  more  as  protection  against  the  hot  drying 
winds  of  summer;  hence,  they  are  generally  set  on  southerly  boundaries. 

Ejfect  of  Wind  Velocity. — Of  quantitative  data  on  windbreak  effects, 
little  is  available.  The  increased  snow  deposit  in  places  sheltered  from 
the  full  sweep  of  the  wind  is  a  matter  of  common  observation.  After  the 
snow  has  fallen  the  windbreak  acts  to  preserve  it  from  evaporation  by 
protecting  it  from  the  full  force  of  the  wind.  Fernow^^  states  that 
snow  evaporates  ten  times  as  fast  in  warm  wind  (velocity  not  stated) 
as  in  calm  air.  Provided  the  snow  accumulation  is  not  great  enough 
to  injure  the  tops  of  young  trees  this  effect  must  be  beneficial  since 
data  to  be  introduced  show  the  great  power  of  snow  in  protecting  roots 


282 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


against  freezing.  How  much  the  windbreak  prevents  the  drying  out 
of  the  tree  tops  during  the  high,  desiccating  cold  winds  of  winter  is  a 
matter  which  with  present  data  can  be  only  conjectured. 

Certain  experiments  have  shown  that  "with  the  temperature  of  the  air  at 
84  and  a  relative  humidity  of  50  per  cent,  evaporation  with  the  wind  blowing  at 
5  miles  an  hour  was  2.2  times  greater  than  in  the  calm;  at  10  miles  3.8;  at  15 
miles  4.9;  at  20  miles  5.7;  at  25  miles  6.1  and  at  30  miles  per  hour  the  wind  would 
evaporate  6.3  times  as  much  water  as  a  calm  atmosphere  of  the  same  temperature 
and  humidity. "*° 

Bates^^  found,  in  comparing  wind  movements  in  the  open  with  those  at  a 
leeward  point  distant  from  the  windbreak  five  times  its  height,  that  "a  wind 
which  reaches  a  velocity  of  25  miles  per  hour  in  the  open  will,  in  the  shelter  of  a 
good  windbreak,  have  a  velocity  of  .    .    .   only  5  miles  per  hour." 

Combining  these  sets  of  figures,  the  evaporation  in  this  case  would 
be  only  39  per  cent,  of  that  in  the  open.  Figure  29,  reproduced  from 
Bates'  study,  shows  the  percentage  of  protection  to  increase  with  the 
wind  velocity. 

100 

90 

80 

^10 

I  50 

^  30 
20 

to 

0  t)  lu  lb  21) 

"Wind  Velocity  in  Open(miIes  per  hour) 

Fig.  29. — Wind  at  points  five   times  the  heights  of  windbreak  to  leeward,   in  terms  of 
wind  in  open.      (After  Bates^^) 

Effect  on  Evaporation. — Card^'  in  Nebraska  determined  the  rates  of  evapo- 
ration at  different  distances  from  a  windbreak  8  rods  wide  and  25  to  40 
feet  high.  Though  these  observations  were  made  in  summer,  they  are  somewhat 
indicative  of  winter  conditions  and  furthermore  they  have  an  important  bearing 
on  the  state  of  trees  as  they  approach  dormancy.  If  the  evaporation  on  the 
windward  side  of  the  windbreak  during  all  the  time  that  drying  winds  were 
blowing  be  represented  by  100,  then  the  evaporation  at  a  point  12  rods  distant 
on  the  leeward  side  would  be  proportionally  83  and  at  3  rods  distant  it  would  be 
55.  During  a  period  of  high  though  not  particularly  dry  wind  the  respective 
rates  were  as  100  to  67  to  29.  Numerous  interesting  studies  of  evaporation 
rates  are  reported  by  Bates,  as  shown  in  Table  25,  arranged  from  his  data. 

Effect  on  Soil  Moisture. — The  importance  of  soil  moisture  in  relation 
to  winter  drought  has  been  shown.  For  this  reason,  Card's  determi- 
nations of  soil  moisture  at  varying  distances  on  the  leeward  side  of  a  wind- 


V 

' 

\ 

^^ 

C^^  , 

1 

^^"■"^^^rro^.^nn. 

\ 

-iii:il_tf5^2__ 

\ 

\ 

V          M/W/ 

TE  PINE  BEJJL — 

WINTER  INJURY 


283 


Table  25. — Mean  Efficiency  of  Windbreaks  in  Area  of  Greatest 
Protection  {After  Bates^^) 


(Area 

12  times  as  wide  as  height  of  trees)    . 

Kind  of  windbreak 

Width, 
feet 

Height, 
feet 

Moisture  saved  at  different 
velocities,  per  cent. 

Period  of 

5 

10 

,. 

20 

Cottonwood  grove  (underplanted) 

25 
100 

75 
20 
50 

70 

40 
23 
32 

23.9 
31.  1 
12.3 

11.7 

12.8 
26.0 

31.9 
33.3 

18.6 

13.9 

20.2 
27.2 

28.7 

38.7 
35.8 
26.6 

15.  5 

23.7 
27.2 

40.1 

33.4 

17.0 

25.8 
27.5 

July,  Sept. 
Nov. 

Cottonwood  row  (natural  density) 
Cottonwood     belt     (no     low 

branches) 

Cottonwood  row  (reinforced  with 

ash)                 

June,  July,  Aug. 
Aug.,  Sept. 
Sept 

Osage      orange       hedge        (lower 

branches  trimmed) 
Mulberry,  single  row 

June,  July,  Aug. 
Aug. 

break  are  of  particular  interest.  Table  26,  arranged  from  his  report 
of  determinations  made  November  5,  shows  a  difference  well  worth 
consideration,  particularly  as  they  were  made  at  the  approach  of  winter. 
Assuming,  as  Card  does,  that  soil  moisture  up  to  10  per  cent,  is  not 
available  for  plants,  the  average  available  moisture  up  to  a  distance  of 
about  7  rods  was  2.55  per  cent.;  beyond  that  point  it  was  0.65  per  cent. 

Table  26. — Soil  Moisture  at  Varying  Distances  from  a  Windbreak^' 


Distance  (rods) 

Percentage  of  moisture 

Available  for  plants 

1 

14.0 

4.0 

3 

12.6 

2.6 

5 

11.3 

1.3 

7 

12.3 

2.3 

9 

10.7 

0.7 

11 

10.5 

0.5 

13 

10.0 

0.6 

15 

10  s 

0.8 

The  area  protected  by  a  windbreak  is  variable.  It  has  been  stated 
that  in  the  Rhone  valley  each  foot  in  the  height  of  a  windbreak  protects 
plants  for  11  feet  to  the  leeward. ^^  From  rather  general  observations  in 
Iowa  and  Nebraska  it  has  been  estimated  that  a  rod  of  ground  is  sheltered 
for  each  foot  in  height  of  the  windbreak,  and  other  estimates  state  that  a 
windbreak  25  feet  in  height  will  protect  10  rods  of  orchard.  Bates 
found  that  the  area  extended  on  the  average  not  more  than  20  times  the 
height  of  the  windbreak;  at  this  distance  the  wind  velocities  were  found 
to  be  almost  as  great  as  on  the  windward  side.  Card's  soil  moisture 
determinations  indicate  that  for  this  windbreak  the  effects  were  not 


284  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

evident  beyond  7  rods.  Unfortunately  these  figures  were  made  in  an 
open  field  and  there  is  at  present  no  means  of  stating  just  to  what  extent 
the  orchard  will  protect  itself  at  points  beyond  the  sheltering  effects  of 
the  windbreak,  though  observation  indicates  that  it  does  to  a  considerable 
extent.  Injury  from  cold  drying  winds  in  the  1903-1904  winter  was 
found  to  be  more  severe  in  the  outside  rows  of  many  orchards. 

INJURIES  CHARACTERISTIC  OF  LATE  WINTER  CONDITIONS 

Primarily  all  winter  injuries  are  induced  by  cold.  This  fact  should 
be  kept  in  view  though  for  convenience  the  late  winter  injuries  are  treated 
as  due  to  warm  weather.  It  is  not  the  heat  that  does  the  harm  but  cold 
weather,  even  in  moderate  degree,  following  warm  weather.  In  one 
form  or  another,  all  fruit  growing  sections  in  temperate  regions  suffer 
through  injuries  proceeding  from  these  causes. 

The  Rest  Period 

Discussion  of  the  rest  period  at  this  point  should  not  be  taken  to  mean 
that  it  is  regarded  among  the  effects  of  temperature;  it  is  considered  here 
very  briefly  because  of  its  relation  to  them.  Periodicity  of  growth  is 
found  in  plants  wherever  they  are;  equatorial  regions  with  uniform 
temperatures  present  the  phenomenon  of  plants  in  the  resting  stage  while 
others  are  in  growth.  Sometimes  on  the  same  tree  one  branch  is  resting 
while  others  are  growing.  Other  factors  than  temperature  are  undoubt- 
edly concerned  with  the  inception  and  with  the  end  of  the  rest  period. 

The  dormant  season  should  not  be  confused  with  the  rest  period, 
though  the  two  overlap  more  or  less ;  in  temperate  regions  the  former  may 
begin  after — or  before — and  generally  extends  beyond,  the  latter.  In 
the  peach,  for  example,  the  rest  period  may  begin  to  ''break"  in  January 
though  the  temperatures  prevailing  may  prolong  the  dormant  season 
into  April.  The  rest  period  is  not  a  time  of  complete  cessation  of  plant 
activities.  The  activities  commonly  recognized  as  growth  are  at  a 
standstill,  but  other  functions,  undoubtedly  of  equal  necessity  to  the 
l^lant,  are  active.     The  beginning  and  end  are  probably  gradual  processes. 

If  an  attempt  is  made  to  force  peach  trees  into  growth  in  a  greenhouse 
during  November  or  early  December  little  success  is  attained;  if  the 
attempt  is  made  in  late  December  less  difficulty  is  encountered  while  in 
January  there  would  be  still  less  difficulty.  In  the  first  instance  the 
trees  are  in  the  rest  period;  in  the  second,  the  rest  period  is  breaking. 
In  the  first  case,  no  matter  how  favorable  the  environment,  there  is  no 
response;  in  the  second,  the  response  is  rapid  whenever  the  environment 
is  suitable. 

Chandler^^  shows  an  interesting  parallelism  between  the  percentage 
of  buds  killed  in  1905-1906  and  the  percentage  of  buds  of  the  same 
varieties  that  could  be  forced  into  development  early  in  the  following 


WINTER  INJURY 


285 


winter.  The  data  are  summarized  in  Table  27,  which  is  arranged  from  a 
more  detailed  statement  in  Chandler's  report.  The  relation  is  close 
enough  to  indicate  why  a  given  variety,  of  the  Persian  type  for  example, 
may  be  tender  in  the  south  where  its  rest  period  is  likely  to  be  broken 
and  still  be  hardy  in  the  north  where  cold  weather  is  constant,  or  why  in 
the  same  orchard  it  may  be  hardy  during  a  winter  of  steady  and  fairly 
severe  cold  and  still  be  tender  during  a  mild  winter. 

Recent  studies  indicate  some  correlation,  even  in  Minnesota,  between 
hardiness  and  the  intensity  of  the  rest  period  in  certain  plums,  as  shown 
in  Table  28.  These  suggest  that  the  rest  period  may  be  more  important 
in  the  north  than  it  generally  has  been  considered,  though  they  do  not 
explain  observed  differences  in  bud  killing  early  in  the  winter. 

T.^£LE  27. — Percentage  of  Buds  Starting  Early  and  of  Buds  Killed''' 


Group 

Percentage  of 
buds  started 
Dec.  12,  1906 

Percentage  of 

buds  started  by 

Dec.  22,  1906 

Percentage  of 

buds  killed  in 

1905-1906 

Hill's  Chili  type 

3.6 
0.0 

0.0 

0.0 

27.9 

12.6 

40.7                      39.7 

Chinese  Cling  type 

Chinese  Cling,   excluding   Elberta, 
a  hybrid 

13.0 

6.7 

8.7 

86.7 

65.7 

51.2 
44.3 

50.6 

Heath  Cling  type 

79.1 

78.9 

Table  28. — Time  Required  for  Blooming  under  Laboratory  Conditions  at 
Different  Intervals  During  the  Winter 

{After  Straushaugh^^^) 


Stella  (semi-hardy) 

Tonka  (semi-hardy) 

Assiniboine  (hardy) 

Date 

collected 

Date  of 

Days 

Date  of 

Days 

Date  of 

Days 

bloom 

required 

bloom 

required 

bloom 

required 

Oct.     3... 

Oct.    17 

15 

Oct.    17 

15 

Did  not  bloom 

Nov.    8... 

Nov.  22 

15 

Nov.  22 

15 

Did  not  bloom 

Nov.  19... 

Dec.     4 

16 

Dec.     4 

16 

Did  not  bloom 

Jan.   24... 

Feb.     2 

10 

Feb.     2 

10 

Feb.   18 

26 

Feb.     6... 

Feb.   15 

10 

Feb.   15 

10 

Feb.  23 

18 

Feb.  21... 

Mar.     2 

11 

Mar.    2 

11 

Mar.    8 

17 

Feb.  28... 

Mar.     7 

9 

Mar.    7 

9 

Mar.  14 

16 

Mar.    5.. 

Mar.  13 

9 

Mar.  13 

9 

Mar.  19 

,5 

Different  plants  appear  to  have  rest  periods  of  unequal  length;  in  fact 
some,  such  as  certain  spiraeas,  seem  to  have  none.  However,  the  rest 
period  for  each  plant  seems  to  be  fairly  constant  provided  no  disturbing 


286  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

influence  acts  upon  the  plant.  It  follows,  then,  that  the  earlier  the  plant 
enters  upon  its  period  of  rest  the  earlier  the  period  is  over.  This  is  a 
matter  of  some  practical  import,  as  appears  later. 

The  rest  period  can  be  shortened,  or  broken,  by  various  treatments. 
Etherization,  light,  wounding,  desiccation,  hot-water  baths  and  exposure 
to  freezing  all  bring  it  to  an  early  end.  For  the  forcing  of  certain  flowers, 
such  as  lilacs,  etherization  is  sometimes  used;  the  greenhouse  man  who 
wishes  to  force  fruits  exposes  the  trees  to  cold.  Northern  greenhouses 
in  Europe  can  force  fruit  and  have  it  on  the  markets  somewhat  in  advance 
of  the  greenhouse  fruit  crop  from  many  more  southern  parts  because  the 
trees  can  be  exposed  to  a  freezing  temperature  earlier  in  the  north  and 
the  rest  period  broken  earlier.  For  the  orchardist,  however,  the  chief 
interest  is  in  prolonging  the  rest  period;  this  can  be  done  in  some  cases, 
discussed  later,  by  postponing  its  advent.  In  northern  sections,  though 
the  temperatures  are  undoubtedly  severe  enough  early  in  the  winter  to 
break  the  rest  period,  they  are  low  enough  to  prolong  dormancy  and  the 
rest  period  is  relatively  of  less  importance  there.  Farther  south,  where 
warm  periods  come  during  the  winter,  it  is  of  much  greater  significance. 

The  exact  natures  of  the  changes  involved  in  the  beginning  and  the  end  of  the 
rest  period  are  not  known.  A  puzzling  fact  is  mentioned  by  Schimper:  A  low 
temperature  in  the  growing  season  will  not  have  the  same  effect  as  in  the  dormant 
season;  the  change  of  starch  to  sugar  in  the  potato  accompanying  cold  in  the 
winter  is  not  dupUcated  in  the  summer.  Since  ordinary  growing  temperatures 
are  without  effect  on  the  rest  period,  chemical  changes  appear  not  to  be  the  con- 
trolUng  factors.  Since  time  is  a  recognized  factor  a  physical  change  is  suggested. 
It  seems  significant  that  all  processes  known  to  shorten  the  rest  period  are  known 
also  to  increase  permeability. 

Injuries  to  Fruit  Buds 

The  killing  of  fruit  buds  which  have  started  into  activity  is  more 
evident  in  southern  sections.  Whitten^i"  discusses  winter  killing  of  the 
peach  in  Missouri  as  of  this  nature.  He  states:  "The  growth  of  buds 
during  warm  weather  in  winter  renders  them  very  susceptible  to  injury 
from  subsequent  freezing.  This  is  the  most  common  cause  of  winter 
killing  to  peach  buds  in  this  state.  Very  often  a  warm  spell  as  early  as 
February  causes  peach  buds  to  make  considerable  growth.  If  growth 
starts  to  any  great  extent  the  subsequent  cold  weather  is  almost  sure  to 
kill  the  buds."  Chandler^^  states  that  "there  has  very  seldom  been  a 
year  when  buds  in  the  peach  section  of  southern  Missouri  have  not  been 
started  sufficiently  by  Feb.  1  to  be  killed  by  a  temperature  considerably 
higher  than  would  be  required  to  kill  buds  in  northern  Missouri,  or 
certainly  in  Michigan,  New  York  or  New  England  on  the  same  date." 

It  is  possible  that  occasionally  the  injury  in  these  cases  of  warm 
weather  followed  by  cold  is  due  merely  to  the  sudden  drop  in  temperature. 


WINTER  INJURY 


287 


Indeed,  Chandler'^  cites  convincing  evidence  to  this  effect:  "In  the 
year  of  1901-1902  all  of  the  buds  were  killed  at  the  Missouri  Experiment 
Station  orchard  by  a  temperature  of  —  23°F.  on  Dec.  20.  In  1902- 
1903  practically  all  buds  were  killed  by  a  temperature  of  —  15°F.  on  Feb. 
17.  In  1903-1904  buds  were  killed  on  all  varieties  except  General  Lee, 
Chinese  Cling,  Thurber,  Carman,  Gold  Drop,  Triumph  and  Lewis  by 
a  temperature  of  —  14°F.  on  Jan.  29.  During  the  winter  of  1904-1905 
nearly  all  the  buds  were  killed,  yet  practically  all  trees  had  a  few  left 
alive  and  Triumph  and  Lewis  a  fair  crop  following  a  temperature  of 
-25°F.  on  Feb.  13.  ...  on  Jan.  12,  1909,  practically  all  the  buds  were 
killed  except  on  the  most  hardy  varieties  by  a  temperature  of  —  11°F.  In 
fact,  fewer  peaches  were  borne  at  Columbia  following  the  winter  of  1908- 
1909  than  following  the  winter  of  1904-1905  when  the  temperature  fell 
to  —  25°F.  on  Feb.  13.  ...  there  was  not  more  warm  weather  to  start 
the  buds  preceding  the  freeze  of  Jan.  12,  1909,  at  Columbia  .  .  than 
preceding  the  freeze  of  Feb.  13,  1905,  at  Columbia. 

"It  would  hardly  seem  possible  that  the  buds  in  either  case  could 
have  been  started  into  slight  growth  preceding  the  freeze.  Buds  start 
very  slowly  even  at  high  temperature  early  in  January.  .  .  .  the  low 
temperature  of  Jan.  12,  1909,  came  suddenly  following  high  temperature 
while  that  of  Feb.  13,  1905,  came  following  42  days  of  rather  low  tempera- 
ture. For  16  days  the  maximum  temperature  did  not  go  above  the 
freezing  point. " 

Chandler  suggests  two  possible  reasons  for  buds  surviving  the  colder 
temperature  of  the  1904-1905  wint-er:  the  long  exposure  to  low  tempera- 
ture which  hardened  them  and  the  very  slow  falling  of  the  temperatures. 

Changes  in  Water  Content  of  Buds  During  Winter. — There  is,  how- 
ever, abundant  evidence  that  development  in  peach  buds  during  warm 
periods  of  the  winter  is  frequently  a  contributing  factor  in  winter  injury. 
Investigations  in  Maryland  show  a  progressive  change  which  easily  may 
be  accelerated  by  pronounced  warm  weather.^^     It  seems  significant  that 


Table  29.- 

—Water  Content  of  Peach  Fruit  Buds 
(After  Johnston^'>) 

Date   of 

sample 

Average  green  weight 
(grams) 

Average  dry  weight 
(grams) 

Ratio  water  con- 
tent   to    green 
weight 

Ratio  water  con- 
tent to  dry  weight 

Elberta 

Greens- 
boro 

Elberta 

Greens- 
boro 

Elberta 

Greens- 
boro 

Elberta 

Greens- 
boro 

Nov.  8 

0.124 
0.  144 
0.  144 
0.164 
0.327 
1.050 

0.121 
0.129 
0.123 
0.128 
0.220 
0.750 

0.073 
0.079 
0.082 
0.082 
0.  115 
0.205 

0.073 
0.073 
0.075 
0.075 
0.092 
0.180 

0.41 
0.46 
0.43 
0.49 
0.65 
0.80 

0.40 
0.43 
0.38 
0.42 
0.58 
0.76 

0.84 
0.76 
0.99 
1.85 
4.  12 

0.65 

Dec.  6 

0.76 

Jan.  7     

0.62 

Feb.  7 

Mar.  7 

Mar.  28 

0.71 
1.37 
3.17 

288  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

the  more  tender  variety  of  the  two  studied  shows  this  change  in  greater 
degree. 

Contributing  Factors. — Roberts, ^"^^  in  Wisconsin,  investigating  blos- 
som bud  kilHng  in  the  sour  cherry,  concluded  that  suceptibility  is  in  direct 
relation  to  the  degree  of  advancement,  the  more  advanced  blossoms 
suffering  most.  He  states:  "The  amount  of  injury  is  in  relation  to 
the  degree  of  development  of  the  blossom  buds,  which,  in  turn,  is  usually 
in  [inverse]  proportion  to  the  amount  of  growth  the  tree  is  making." 
These  conclusions  were  reached  after  microscopic  investigation  as  well 
as  field  studies. 

The  position  of  the  hardiest  buds  was  investigated  by  Chandler^^ 
whose  report  follows,  in  part:  .  .  .  "the  hardy  buds  are  those  borne  at 
the  base  of  the  whips  (last  year's  growth).  ...  at  the  base  of  the 
whips  on  trees  not  cut  back  only  a  slightly  larger  percentage  of  buds  were 
killed  than  were  killed  at  the  tips  of  cut  back  trees.  .  .  .  Now  it  is 
possible  to  head  back  so  severely  that  no  fruit  buds  will  be  formed  except 
at  the  outer  end  of  the  branches.  This  is  especially  true  if  the  tree  has 
a  narrow  dense  head.  ...  If  the  tree  be  spreading  in  form,  heading 
back  is  not  so  likely  to  cause  the  next  season's  wood  to  be  in  very  long 
whips  that  either  have  branches  at  the  basal  nodes  instead  of  fruit  buds, 
or  have  the  leaves  at  these  basal  nodes  killed  by  the  shade  before  fruit 
buds  can  be  formed.  This  is  true  because  the  spreading  heads  would 
afford  room  for  a  larger  number  of  whips  to  grow  and  obtain  light,  and 
the  larger  the  number  of  nearly  equal  growing  whips,  other  conditions 
of  the  tree  being  equal,  the  shorter  necessarily  will  be  the  growth  in 
each  whip."  Data  are  cited  showing  a  loss  of  60.2  per  cent,  of  fruit 
buds  on  a  large  low-growing,  spreading  Oldmixon  as  compared  with 
86.4  per  cent,  on  a  tree  of  the  same  variety  making  very  large,  upright 
growth  and  90.8  per  cent,  on  still  another  Oldmixon  making  small 
upright  growth. 

Protective  Measures. — Late  entrance  into  the  resting  stage  has  been 
said  above  to  cause  a  delay  in  breaking  the  rest  period.  This  may  be 
effected  in  a  number  of  ways. 

Pruning. — One  of  the  means  of  inducing  late  growth  and  late  entrance 
into  the  resting  period  is  pruning  heavily  enough  to  stimulate  vigorous 
growth.  Chandler^^  reports  results  of  investigations  in  forcing  twigs 
of  a  large  number  of  peach  varieties  which  he  summarizes  as  follows: 

"Average  per  cent,  started  on  trees  making  large  growth 

(cut  back) 20.5 

Average  per  cent,  started  on  trees  making  small  growth 

(not  cut  back) 31.2 

Number  of  varieties  in  which  trees  not  cut  back  started  first .  .  20 

Number  of  varieties  in  which  trees  cut  back  started  first 3. 

Number  in  which  both  started  about  equally 4. 


WINTER  INJURY 


280 


"  .  .  .  If  we  take  the  average  of  buds  started  on  twigs  taken 
December  22,  or  later,  that  is,  when  the  resting  period  is  nearly  ended,  we 
have ; — 

For  trees  making  large  growth  (cut  back)  28.3  per  cent,   started. 

For  trees  making  smaller  growth  (not  cut  back)  48.6  per  cent,  started. 

"Taking  only  those  varieties  in  which  one  tree  had  60  per  cent 
of  the  buds  started,  and  therefore  may  be  considered  to  have  finished  its 
resting  period,  we  have  as  an  average — 

On  trees  making  large  growth  (cut  back)  44.3  per  cent,  of  the  buds 
started; 

On  trees  making  smaller  growth  (not  cut  back)  83.4  per  cent,  of  the 
buds  started." 

It  is  apparent  that  the  more  favorable  the  conditions  become  for 
breaking  of  the  rest  period  the  more  evident  becomes  the  restraining 
influence  of  late  maturity. 

That  this  retardation  of  development  by  pruning  actually  results  in 
lessening  winter  injury  of  the  type  under  discussion  is  shown  by  numerous 
instances  cited  by  Chandler.  After  a  succession  of  warm  days  followed 
by  a  fall  to  —  3°F.,  which  would  hardly  kill  any  considerable  number  of 
buds  unless  they  had  started  into  development,  a  count  was  made  of 
dead  buds  on  pruned  and  unpruned  trees.  Table  30,  arranged  from 
Chandler's  data,  shows  one  instance.  Even  more  striking  is  his  enumera- 
tion of  results  at  Brandsville,  Missouri,  following  the  freeze  of  Mar.  16, 
1911,  when  98.08  per  cent,  of  the  buds  on  unpruned  trees  were  killed 
while  only  81.9  per  cent,  were  killed  on  the  severely  pruned  trees. ^*     The 

T.\BLE  30. — Buds  Ivjlled  at   —  3°F.  on  Pruned  and  Unpruned  Trees'^ 


Variety 


Per  cent,  killed 


Pruned 


Unpruned 


Elberta 

Oldmixon  Free 

Triumph 

Lewis 

Early  Tillotson 

Average 


48.5 
62.9 
30.0 
16.0 
23.9 

36.2 


67.8 
78.0 
59.1 
25.7 
.54.7 

59.8 


killing  on  the  pruned  trees  seems  high  but  18.1  per  cent,  of  peach  buds 
may  produce  a  full  crop,  as  they  did  in  this  instance,  while  the  unpruned 
trees  bore  only  a  few  peaches. 

Fertilization    and    Cultivation. — Nitrogenous    fertilizers,    stimulating 
vegetative  growth,  have  much  the  same  effect  as  pruning,  according  to 


290 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Chandler.  In  one  case,  at  Brandsville,  Mar.  16,  1911,  unfertilized  trees 
lost  98.4  per  cent,  of  their  buds  while  trees  fertilized  with  ammonium 
sulfate  lost  77.6  per  cent,  and  those  which  had  received  nitrate  of  soda 
lost  87.1  per  cent.  In  one  instance  the  fertilizer  saved  enough  buds  to 
make  a  full  crop,  in  the  other  enough  for  a  fair  crop. 

Late  cultivation  has  been  reported  to  have  the  same  results  in 
retarding  the  rest  period  and  increasing  hardiness. 

Thinning. — Thinning  has  been  observed  to  have  beneficial  effects 
on  hardiness.  Chandler^^  cites  a  case  in  which  buds  of  certain  varieties 
survived  a  winter  that  killed  those  of  most  varieties.  These  trees  then 
bore  a  full  crop  but  in  the  following  winter  their  fruit  buds  succumbed 
while  the  varieties  tender  in  the  previous  year  survived.  To  secure 
experimental  data  the  fruit  on  half  of  each  of  several  heavily  loaded  trees 
was  thinned  with  the  results  shown  in  Table  31.     When  the  experiment 

Table  31. — Effect  of  Thinning  Fkuit  on  Hardiness  of  Buds'^ 


Percentage  of  buds  killed 

Variety 

Thinned 

Unthinned 

Seedling  . 

18.5 
31.6 
44.5 
41.7 
40.9 

35.4 

58  9 

Elberta  Seedling 

36  7 

Oldmixon  Cling.  .  . 

53  4 

Poole's  Favorite 

52  8 

Poole's  Favorite  No.  2 

55  4 

Average 

51.4 

was  repeated  in  1908,''*  the  effects  of  the  freeze  of  Jan.  12,  1909,  following 
weather  such  that  all  buds  may  be  regarded  as  dormant  at  the  time,  were 
quite  different,  the  unthinned  limbs  losing  92.5  and  the  thinned  93.2 
per  cent,  of  their  buds.  Laboratory  results  are  reported  as  follows: 
"These  results  suggest  that  thinning  has  its  effect  on  the  rest  period 
rather  than  on  the  intrinsic  hardiness  of  the  buds.  Where  the  tree  is 
bent  under  a  heavy  load  and  under  the  strain  of  bearing  a  heavy  crop, 
as  when  it  is  not  thinned,  the  moisture  supply  probably  being  partially 
shut  off,  the  same  condition  will  prevail,  at  least  to  some  extent,  as  when 
the  trees  are  not  cultivated;  they  will  become  dormant  earlier  and  end 
their  rest  period  earlier.  Thus  thinning,  like  heavy  pruning  and  ferti- 
lizing with  nitrogen  can  be  expected  to  increase  the  hardiness  of  peach 
fruit  buds  only  in  climates  like  that  from  Central  Missouri  South,  where 
there  is  likely  to  be  weather  warm  enough  to  start  the  buds  into  growth 
before  the  effect  of  the  rest  period  ends." 


WINTER  INJURY 


291 


Whitewashing  and  Shading. — Sunlight  is  an  important  influence 
in  forcing  buds.^^"  The  spraying  of  peach  trees  with  whitewash  resulted 
in  a  reduction  of  heat  absorption,  with  the  effects  on  blossoming  shown 
in  Table  32,  arranged  from  a  similar  table  by  Whitten.     These  data 

Table  32. — Blossoming  Dates  of  Whitewashed  Peach  Trees^i" 


First  blossoms 

Full  bloom 

Last  blossoms 

Variety 

White- 
washed 

Not  white- 
washed 

White- 
washed 

Not  white- 
washed 

White- 
washed 

Not  white- 
washed 

Heath  Cling 

Wonderful 

Rivers'  Early  .  . 
Silver  Medvil ,  .  . 

Apr.  13 
Apr.  14 
Apr.  13 
Apr.  13 

Apr.  11 
Apr.  11 
Apr.    9 
Apr.    7 

Apr.  21 
Apr.  22 
Apr.  — 
Apr.  18 

Apr.  18 
Apr.  18 
Apr.  21 
Apr.  13 

Apr.  29 
Apr.  29 
Apr.  29 
Apr.  28 

Apr.  27 
Apr.  25 
Apr.  27 
Apr.  21 

do  not,  however,  show  the  full  force  of  reduced  sunlight  absorption  as  its 
effectiveness  would  be  greatest  during  the  warm  periods  of  winter 
while  atmospheric  temperatures  are  lower  and  when  even  slight  develop- 
ment may  result  in  winter-killing.  Somewhat  similar  results  have 
been  obtained  with  plums  in  Ontario,  but  not  with  the  apple,  "^  which 
blossoms  much  later  when  the  air  temperature  has  greater  influence 
in  proportion  to  heat  of  insolation  than  it  has  earlier  in  the  season. 
Even  farther  south,  because  of  the  difficulty  in  keeping  trees  well  covered 
with  whitewash  and  the  consequent  expense  involved  together  with  the 
ever-present  possibility  of  conditions  that  will  kill  buds  despite  the 
covering,  this  method  is  little  used. 

Board  shelters  have  been  found  even  more  efficacious  than  white- 
washing but  again  the  expense  involved  precludes  their  use.^^*'  However, 
a  choice  tree  or  two  can  sometimes  be  located  on  the  shady  side  of  a 
building  to  good  effect  and  sometimes  a  hill  can  be  of  advantage  in  secur- 
ing partial  shade  from  the  low  midwinter  sun  for  a  good  sized  orchard. 

In  General. — The  peach  has  been  used  as  illustrative  matter  here, 
because  it  has  been  studied  the  most  thoroughly.  More  or  less  similar 
appHcation  may  be  made  to  Japanese  plums,  apricots,  almonds  and 
cherries. 

Finally  it  should  be  emphasized  that  the  breaking  of  the  rest  period 
in  the  buds  is  entirely  independent  of  the  roots  and  that  efforts  to  retard 
blossom  development  during  warm  periods  in  the  winter  by  mulching  the 
ground  to  keep  it  frozen  or  by  spreading  snow  on  the  ground  around  the 
trees  are  absolutely  wasted.  Trees  open  their  buds  while  the  soil  about 
the  roots  is  still  frozen  or  after  they  have  been  cut  away  from  the  roots. 
Time  and  again  evidence  to  this  effect  has  been  presented  and  afterward 
the  same  useless  effort  repeated.  The  winter  rest  period  of  buds  can  be 
influenced  through  the  roots  during  the  growing  season  only. 


292  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Attention  must  be  called  to  the  greater  application  of  the  principles 
just  outlined  the  farther  south  the  location  and  their  diminished  applica- 
bility northward.  Wiegand^^^  reported  that  in  New  York  fruit  buds 
did  not  grow  from  about  Nov.  15  until  about  Mar.  1,  when  apple  and 
apricot  buds  began  a  relatively  rapid  development  culminating  in  open 
blossoms  8  and  7  weeks  later  respectively.  Peach  buds  did  not  begin 
their  spring  growth  until  Mar.  23  and  came  into  blossom  with  the  apricots 
on  Apr.  23.  It  appears  from  these  observations  that  the  cooler  and 
shorter  growing  season  in  the  north,  though  it  stops  growth  earlier 
by  the  calendar,  makes  the  peach  buds  less  advanced  at  the  onset  of  the 
dormant  period  and  less  easily  started  into  growth,  while  the  colder 
winters  add  to  this  effect. 

However,  an  interesting  case  is  reported  by  Maynard^^^  in  Massachu- 
setts. Early  in  November,  1884,  peach  buds  appeared  fully  matured. 
Following  warm  weather  late  in  the  month  the  stamens  and  pistils  in- 
creased measurably  in  size  and  the  bud  scales  loosened.  The  minimum 
temperature  to  Dec.  11  was  18°F.;  at  this  time  some  buds  had  been  killed, 
but  the  majority  were  unhurt  and  the  petals  had  begun  to  take  on  color. 
Following  a  minimum  of  10°F.  on  Dec.  19  and  20  all  fruit  buds  were 
destroyed. 

Premature  starting  from  the  rest  period  is,  however,  a  less  common 
occurrence  in  northern  peach  regions.  The  very  practices  recommended 
for  retarding  it,  if  carried  out  too  thoroughly  in  northern  regions,  though 
they  might  conceivably  benefit  the  grower  once  in  20  seasons,  would  in 
the  other  19  make  his  trees  more  liable  to  injury  because  immature  and  he 
would  probably  have  damaged  trees  in  10  of  these  years.  The  southern 
grower  guarding  perhaps  once  against  immaturity  would  suffer  from  pre- 
cocious bud  development  10  times.  Each  grower  must  determine  the 
danger  more  commonly  met  in  his  orchard  and  steer  wide  of  this  particular 
rock,  hoping  he  will  no  more  than  scrape  his  keel  on  the  other.  At  the 
same  time  the  grower  in  ''southern"  regions  may  be  on  the  northern 
limit  for  certain  of  the  southern  peach  groups  and  thus  in  the  same 
orchard  he  may  have  to  contend  with  short  rest  period  in  one  variety 
and  with  immaturity  in  another. 

Injuries  to  Vegetative  Tissues 

Sunscald  is  the  common  name  of  a  late  winter  injury  likely  to  occur 
in  the  north  as  well  as  in  the  south.  It  is  found  on  all  types  of  fruit  trees, 
on  European  chestnut  and  on  various  shade  and  forest  trees.  Very 
small  trees  are  rarely  troubled  by  winter  sunscald  and  trees  old  enough 
to  develop  thick,  scaly  bark  are  less  subject  in  the  parts  so  protected. 
Attention  is  drawn  to  the  injury  by  the  dead  and  dry  appearance  of  the 
bark  on  the  southwest  side  of  the  trunk  where  the  sun  strikes  strongest 
between  noon  and  2  o'clock.     Sometimes  this  area  is  filled  with  a  fer- 


WINTER  INJURY  293 

merited  fluid  and  the  injury  is  called  "sour  sap."  Later  the  bark  may 
loosen  and  fall  away  leaving  an  exposed  area  of  dead  sap-wood.  Many 
trees  pruned  to  an  open  center  are  affected  at  the  crotch  or  even  high  on 
the  south  side  of  those  scaffold  limbs  that  lean  to  the  north.  In  this 
last  position  the  sun's  rays  are  received  nearly  at  right  angles  and  the 
injury  there  is  in  many  cases  very  severe. 

The  chief  importance  of  this  injury  lies  in  its  ultimate  effects  rather 
than  in  its  immediate  results.  It  leads  at  once,  obviously,  to  partial 
obstruction  of  conduction  of  nutrient  and  food  materials,  but  of  greater 
moment  is  the  exposure  to  fungi  and  borers  and  the  resultant  mechanical 
weakening  of  the  tree. 

Distinguished  from  Summer  Sunscald  and  Injuries  Associated  with 
Immaturity. — Distinction  between  this  type  and  winter  killing  associated 
with  immaturity  on  the  one  hand  and  between  this  type  and  summer 
sunscald  on  the  other  is  sometimes  difficult.  In  fact  some  writers  have 
denied  the  existence  of  sunscald  and  some  have  maintained  that  summer 
heat  never  kills  bark.  Evidence  showing  that  bark  is  sometimes  killed 
by  high  temperatures  is  easily  gathered.  Fisher^*  quotes  Vonhausen  as 
finding,  between  the  sapwood  and  bark,  a  temperature  of  120°F.  when  the 
air  temperature  was  91°F.,  while  in  Bavaria,  Hartig  observed  a  tempera- 
ture of  131°F.  between  the  bark  and  sapwood  of  some  isolated  80-year 
old  spruce  trees.  This  is  a  lethal  temperature  for  leaves  and  herbaceous 
shoots  and  is  presumably  so  for  cambium  cells.  In  forests  when  an  open- 
ing is  made,  the  standing  trees  on  the  north  side  of  the  clearing  in  many 
cases  show  the  sunscald  high  on  the  south  side  of  their  trunks.  Young 
apple  trees  set  late  in  the  spring  in  sandy  soil  and  headed  back  so  they 
had  little  protecting  top,  have  been  observed  even  in  New  Hampshire, 
to  show  severe  sunscald  by  midsummer. 

Caution  should  be  observed,  however,  in  attributing  all  injuries  on  the 
southwest  side  of  the  tree  to  late  winter  sunscald.  Balmer^'-  describing 
the  effects  of  a  November  freeze  in  Washington  mentions  that  trees  with 
high  trunks,  leaning  from  the  afternoon  sun,  suffered  notably.  In  several 
cases  the  bark  on  the  southwest  side  of  the  trunks  split  open.  Investiga- 
tors seem  to  have  overlooked  the  possible  effects  of  radiation  in  this 
connection.  It  is  shown  under  Frost  Injury  that  the  temperature 
near  the  soil  on  a  frosty  night  may  be  10°  or  more  lower  than  that  recorded 
by  a  sheltered  thermometer  near  by.  An  October  temperature  of  20°F. 
is  not  uncommon;  with  suitable  radiation  conditions  the  ternperature 
near  the  soil,  if  10°  lower,  would  be  10°F.,  low  enough  to  cause  consider- 
able injury  to  immature  tissues.  Since  somewhat  lower  temperatures 
occur  over  sod  under  these  conditions  than  over  cultivated  ground  the 
occurrence  of  "sunscald"  in  sod  orchards  need  not  be  surprising.  Injury 
of  this  kind  is  obviously  associated  with  immaturity.  Therefore  it  is  not 
safe  to  consider  sunscald  altogether  a  late  winter  injury. 


294  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Moisture  and  Temperature  Conditions  in  the  Affected  Parts. — The 

winter  sunscald,  however,  is  much  more  common.  It  is  not  induced  by 
simple  insolation  but  by  interacting  effects  of  heat  and  cold.  This  is 
quite  evidently  the  malady  described  by  Downing^'*  in  1846  as  "frozen 
sap  blight"  and  rather  confused  with  pear  blight  by  many  of  the  early 
American  pomological  writers.  The  description  by  Downing  clearly 
indicates  this  form,  as  he  includes  Ailanthus,  Spanish  chestnut  and 
catalpa  among  the  plants  affected.  He  attributed  the  trouble  to  sudden 
thawing  and  proposed  as  a  remedy  shading  the  south  side  of  the  trunk 
and  whitewashing.  Somewhat  later  he  recorded  that  on  Dec.  19,  1846, 
a  bright  mild  day,  with  snow  on  the  ground,  a  naked  theremometer  regis- 
tered 97°F.  while  one  with  a  whitewashed  bulb  registered  79°F.^^  Various 
suggestions  as  to  the  way  sunscald  is  brought  about  have  been  made,  in- 
cluding rapid  thawing,  increased  flow  of  sap  followed  by  freezing  so  that 
the  bark  is  pushed  off,  breaking  of  the  rest  period  in  the  warmed  area  and 
alternate  freezing  and  thawing.  Miiller-Thurgau''^  found  in  March  a 
water  content  of  53.8  per  cent,  in  the  bark  on  the  south  side  of  a  plum 
tree  and  48.5  per  cent,  on  the  north  while  the  bark  of  a  tree  wrapped 
with  rushes  showed  moisture  percentages  of  51.5  and  51.3  on  the  south 
and  north  sides  respectively.  He  considered  these  figures  to  corroborate 
the  suggestion  that  a  localized  breaking  of  the  rest  period  subjected  the 
affected  areas  to  injury  from  subsequent  cold. 

The  most  extensive  investigation  on  this  phase  of  winter  killing  is 
that  of  Mix.  ^3*  Particular  attention  was  given  to  the  cambium  since 
this  tissue  suffers  severe  injury  "and  without  injury  to  the  cambium  and 
outermost  xylem  the  bark  would  not  separate  from  the  wood."  Obser- 
vations of  temperature  under  the  bark  on  the  northeast  and  southwest 
sides  of  apple  trunks  showed  no  significant  differences  on  cloudy  days  but 
marked  variations  on  bright  days,  demonstrating  the  warming  effect  of 
the  sun's  rays.  Tables  33  and  34  are  selected  from  data  reported  by 
Mix  from  these  observations  and  are  representative  of  his  more  extended 
figures.  The  temperatures  for  Mar.  10  are  worthy  of  special  attention, 
being  32°F.  on  the  northeast  side  and  69°F.  on  the  southwest  side  at  the 
same  time.  On  Feb.  10,  Mix  observed  on  the  southwest  side  of  one  tree 
a  fall  from  59°  to  27°F.  between  2  o'clock  and  9,  the  air  temperature 
dropping  from  28°  to  19°  F.  in  the  same  time,  while  on  the  northeast  side 
the  temperature  fell  from  25°  to  19°F.  The  temperature  of  the  southwest 
side  dropped  32°F.  while  that  of  the  northeast  side  fell  6°F.  On  another 
tree  the  temperature  on  the  southwest  side  fell  between  5  o'clock  and  6 
(sunset  at  5:30)  from  —0.3°  to  —  14.4°C.  while  on  the  northeast  side  it 
dropped  from  —9.4°  to  —  18.3°C.  This,  it  should  be  emphasized,  was  in 
1  hour.  By  morning  the  temperatures  on  both  sides  were  frequently 
observed  to  be  approximately  equal.  The  southwest  side  of  a  tree  trunk 
is  evidently  subject  to  wider  fluctuations  in  temperature  and  to  more 


WINTER  INJURY 


295 


Table  33. — Tree  Temperatures  on  Cloudy  Days 

(After  Mia- 135) 


Date 


Hour 


Southwest      Northeast 


side, 

degrees 

Centigrade 


side, 

degrees 

Centigrade 


Air,  degrees 
Centigrade 


Jan.  15 
Jan.  16 
Jan.  17 
Jan.  19 
Jan.  20 
Jan.  21 
Jan.  23 
Jan.  24 


11 

00 

30 

30 

00 

11 

40 

00 

10 

10 

•6.9 
3.3 
1.9 

■3.9 
0.0 
0.0 

-2.2 

-0.5 


-7.5 

2.8 
-3.0 
-3.9 
0.0 
0.0 
-2.2 
-0.5 


-5.5 
2.6 

-3.9 

-2.5 
1.1 

-2:2 
0.0 
4.4 


Table  34. — Tree  Temperatures  on  Sunny   Days 

(Data  from  same  tree  as  Table  33) 

(After  Mix^^") 


Date 

Hour 

Southwest 

side, 

degrees 

Centigrade 

Northeast 

side, 

degrees 

Centigrade 

Air,  degrees 
Centigrade 

Jan.  14 

Jan.  26 

Feb.  2 

3:00 
3:25 
1:30 
1:35 
1:05 
2:10 

12:50 
1:00 
2:50 
1:00 
1:00 

12:55 

11:00 
1:30 

12:50 
1:15 
1:00 

-2.8 

1.1 

12.2 

15.0 

12.8 

-0.5 

-4.4 

-6.4 

3.9 

-6.4 

-2.8 

1.7 

-1.9 

20.5 

15.0 

12.2 

11.1 

-12.2 

-2.8 

-1.1 

2.8 

0.8 

-4.4 

-9,4 

-15.0 

-9.4 

-11.4 

-16.1 

-9.7 

-10.0 

0.0 

-3.3 

1.7 

5.0 

-12.2 

-1.4 

0,5 

Feb.  3 

Feb.  4                   

9,4 
1  6 

Feb.  8               

-6.7 

Feb.  9 

Feb.  13 

-8.3 
-11.7 

Feb.  15 

Feb.  23                   

-12.2 
-14  4 

Feb.  24   

Feb.  25 

-5.6 

Feb  26 

Mar    10 

1   1 

Mar.  12     

-4.4 

Mar.  24 

3.9 

Mar.  25 

8.9 

sudden  falling  of  temperature  after  the  sun's  heat  is  withdrawn  at 
sunset.  Even  more  striking  temperature  differences  may  occur  occasion- 
ally. In  fact  Mix  records  a  temperature  of  92°F.  on  the  southwest  side 
on  Feb.  20,  while  the  temperature  on  the  northeast  side  was  35°F. 


296 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


The  effect  of  snow  in  relation  to  sunscald  seems  to  have  escaped  the 
attention  of  writers  on  this  subject.  Sunhght  striking  snow  is  to  a  large 
extent  reflected  and  a  late  winter  snow  is  bound  to  have  no  little  influence 
in  intensifying  the  heating  on  the  southwest  side  of  tree  trunks.  If, 
as  frequently  happens  in  late  winter  in  northern  latitudes,  a  snowfall  dur- 
ing the  night  is  followed  by  a  clear  warm  day  and  a  night  of  considerable 
cold  the  change  in  temperature  of  the  southwest  side  must  be  considerable 
and  abrupt. 

Rapid  freezing,  especially  during  the  first  part  of  the  temperature  fall 
has  been  shown  by  Chandler^*  to  cause  killing  at  a  relatively  high  point. 
These  are  the  very  conditions  just  recorded  and  seem  adequate  to  explain 
killing  by  sunscald  without  any  assumption  that  growth  has  started. 
Artificial  freezings  accompanied  by  microscopic  examination  of  tissues 
made  by  Mix  showed  no  difference  in  hardiness  on  either  side  when  frozen 
under  identical  conditions.  Rapid  freezing  killed  at  —  20°C.  while 
slow  freezing  caused  no  injury  at  —  28°C.  As  spring  advances  these 
tissues  become  less  hardy,  but  equally  on  all  sides  of  the  trunk.  The 
conclusion  seems  inevitable,  therefore,  that  it  is  rapid  freezing  after  sun- 
down that  causes  winter  sunscald. 

Preventive  Measures. — Prevention  of  the  rapid  fall  is  best  effected  by 
keeping  the  day  temperature  down.  Anything  that  will  shade  the  trunk, 
as  a  stake  or  a  bundle  of  corn  stalks,  will  do  this  well.  Whitewash  also, 
because  of  its  low  heat  absorption,  may  be  used  to  advantage. 

Table    35. — Temperatures  of  Whitewashed,  Tarred  and  Untreated  Trees^' 


Air,  degrees 
Centigrade 

Untreated 

Whitewashed                           Tarred 

Date 

Northeast, 
degrees 
Centi- 
grade 

South- 
west, 
degrees 
Centi- 
grade 

Northeast, 
degrees 
Centi- 
grade 

South- 
west, 
degrees 
Centi- 
grade 

Northeast, 
degrees 
Centi- 
grade 

South- 
west, 
degrees 
Centi- 
grade 

Jan.  15 

Jan.  30 

Feb.  4 

Feb.  10 

Feb.  19 

Feb.  20 

Average 

3.9 
-5.6 
0.0 
-1.7 
3.9 
6.1 
1.1 

1.7 

-8.3 
-3.3 
-3.9 
-1.7 
0.0 
-2.6 

11.1 

-4.4 
7.2 
15.0 
17.2 
21.7 
11.3 

0.6 

-8.9 
-4.1 
-6.7 
-2.2 
-0.6 
-3.2 

2.2 

-2.8 
1.1 

-0.6 
5.0 
6.1 
l.S 

3.3 
-4.9 
-0.6 
-1.1 
0.0 
1.7 
-0.3 

20.5 
13.9 
17.8 
29.0 
31.1 
33.3 
24.3 

Table  35,  arranged  from  data  reported  by  Mix,  shows  the  sharp 
contrast  in  sunny  side  temperatures  between  a  whitewashed  and  an 
untreated  tree,  a  difference  that  becomes  more  marked  as  the  tempera- 
tures go  higher.  The  difference  appears  considerable  enough  to  save 
treated  trees  from  sunscald  in  many  cases.  The  same  table  suggests 
also  a  reason  why  gas  tar,  occasionally  applied  as  a  borer  repellant,  is 
said  frequently  to  kill  trees.     The  difi"erence  between  the  temperatures 


WINTER  INJURY 


297 


under  whitewash  and  under  tar  is  due  apparently  to  the  respective  heat 
absorptive  powers  of  white  and  black  colors,  as  their  minimum  early 
morning  temperatures  were  practically  the  same. 

INJURIES  DUE  TO  SUDDEN  COLD 

Though  some  types  of  injury  already  discussed  as  associated  with 
immaturity  of  tissue  might  be  considered  to  belong  in  the  category  of 
injuries  due  to  sudden  cold,  they  may  be  classed  more  correctly  as  due  to 
untimely  cold.  Here,  too,  probably  belongs  the  type  known  as  winter 
suriscald  which  is  discussed  under  late  winter  injuries  but  the  present 
section  is  limited  in  its  application  to  injuries  occasioned  by  a  sudden 
change  from  moderate  cold  to  intense  cold. 

General  Effects. — Chandler^^  has  been  quoted  earlier  as  reporting 
greater  injury  to  plant  tissue  attendant  upon  sudden  lowering  of 
temperature.  His  statement,  however,  should  be  reproduced  here :  "  The 
rate  of  temperature  fall  is  very  important  indeed,  especially  in  case  of 
winter  buds.  In  fact,  apple  buds  can  be  frozen  in  a  chamber  surrounded 
by  salt  and  ice  rapidly  enough  so  that  practically  all  of  them  will  be  killed 
at  a  temperature  of  0°F.,  or  slightly  below,  while  it  is  well  known  that 
they  may  go  through  a  temperature  of  20  to  30°F.  below  zero  with  but 
slight  injury  where  the  temperature  fall  is  not  so  rapid.  .  .  .  the 
killing  temperature  of  rapidly  frozen  twigs  was  4.5°  higher  than  those  of 
the  more  slowly  frozen  twigs  and  even  then  the  buds  of  the  rapidly 
frozen  twigs  killed  the  worst."  Table  36,  chosen  from  several  reported 
by  Chandler,  shows  the  difference  vividly. 


Table  36. 


-Effect  of  Slow  and  Rapid  Temperature  Fall  on  Cherry    Fruit 

BUDS'« 


Variety 

Manner  of  freezing 

Date 

Number 

of 

buds 

Percent- 
age 
killed 

Montmorency 

Montmorency 

Early  Richmond 

Early  Richmond 

Slowly  to     -20°C. 
Rapidly  to  -20°C. 
Slowly  to     -20°C. 
Rapidly  to  -20°C. 

Mar.  2 
Feb.  29 
Mar.  9 
Mar.  14 

163 
130 
297 
263 

3.0 
96.0 

5.0 
98.0 

However,  it  should  be  remembered  that  Chandler  found  also  a  rapid 
fall  to  —  12°C.  more  injurious  than  a  rapid  fall  from  —  12°C.  to  the 
killing  temperature.  This  is  shown  strikingly  in  Table  37,  adapted  from 
a  table  by  Chandler. 

No  data  bearing  on  this  matter  drawn  from  field  observations  are 
available.  Fortunately,  as  Chandler  states,  ''In  this  investigation  it 
was  not  possible  to  cause  the  temperature  to  fall  more  slowly  than  the 
most  rapid  fall  to  be  observed  naturally  in  the  climate  of  this  station 


298  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Table  37. — Effect  of  Rapid  Fall  Early  and  Late  in  the  Freezing  ^s 


Variety 

Manner  of  freezing 

Date 

Number 
of  buds 

Percent- 
age 
killed 

Elberta  peach 

Elberta  peach 

Elberta  peach 

Elberta  peach 

Montmorency  cherry 

Montmorency  cherry 

Montmorency  cherry 

Montmorency  cherry 

Slow    to     -12°;    fast 

-12°  to  -16° 
Fast  to  -12°;   slow 

-12°  to  -16° 
Slow  to  -17.5° 
Fast  to  -16.0° 
Fast   to    -12°;   slow 

to  -20° 
Slow    to     -12°;    fast 

to  -20° 
Fast  to  -20° 
Slow  to  -20° 

Dec.  20 

Dec.    20 

Dec.  20 
Dec.  8 
Feb.  24 

Feb.  27 

Feb.  27 
Mar.  2 

135 

77 

129 
135 
142 

136 

130 
163 

3.7 

71.4 

6.2 
98.5 
75.0 

15.4 

96.0 
3.0 

(Missouri)."  Hence,  the  "slow"  of  Tables  36  and  37  is  the  "fast"  of 
nature.  However,  it  seems  quite  possible  that  certain  "warm  spots" 
in  an  orchard  may  heat  considerably  during  a  clear,  cold  day  only  to 
have  a  very  rapid  drop  in  temperature  following  sunset  and  that  some 
of  the  injury  attributed  to  buds  "starting  growth"  during  winter  is  in 
reality  due  to  a  sudden  and  considerable  drop  of  this  kind.  Nevertheless, 
in  a  large  number  of  cases  when  wholesale  destruction  of  fruit  buds  occurs 
it  can  be  traced  to  some  other  cause. 

Trunk  Splitting. — Trunk  splitting  is  much  more  common  in  forest 
and  shade  trees  and  most  of  the  literature  on  this  type  of  injury  deals 
with  these  trees.  Nevertheless,  it  is  by  no  means  unknown  in  fruit 
trees;  instances  are  on  record  of  fruit  trees  splitting  through  the  trunk. ^^^ 

Close  measurements  in  Europe  have  shown  that  temperatures  under 
the  freezing  point  induce  a  contraction  in  the  trunks  of  various  forest 
trees  which  with  long  continued  freezing  reaches  the  magnitude  of  an 
annual  ring.^''  Deciduous  trees  react  much  more  readily  than  evergreen. 
The  generally  accepted  view  is  that  a  rapid  fall  of  temperature  induces 
a  considerable  contraction  of  the  bark  and  outer  wood  while  the  inner 
wood,  still  at  a  much  higher  temperature,  does  not  shrink  equally; 
hence  the  splitting.  The  cracks  start  generally  at  the  bark  and  proceed 
radially  toward  the  center  of  the  tree  or  even  beyond.  Objection  has 
been  raised  that  clefts  extending  beyond  the  center  could  not  be  caused 
in  this  way  but  if  it  be  assumed  that  the  center  of  the  tree  is  already 
frozen,  those  who  have  cut  frozen  wood  and  know  how  easily  it  splits 
will  have  little  difficulty  in  believing  that  an  initial  cracking  at  the 
periphery  may  be  transmitted  beyond  the  center  because  of  the  glassy 
nature  of  frozen  wood  and  the  pull  of  the  contracting  bark. 


WINTER  INJURY  299 

Wind  may,  as  has  been  suggested, ^2  be  associated  with  this  type  of 
injury  under  certain  circumstances  but  there  can  be  no  doubt  whatever 
that  sphtting  occurs  on  absolutely  still  nights,  the  sharp,  rifle-like 
report  accompanying  the  fissure  being  very  noticeable  under  such  con- 
ditions. Fisher^^  discusses  the  subject  at  some  length.  He  reports  that 
most  frost  cracks  occur  in  cold  weather  between  midnight  and  morning 
and  may  close  again  with  rising  temperature;  further,  that  sometimes  an 
internal  frost  crack  occurs,  the  sap-wood  rending  while  the  bark  holds 
intact.  Hardwoods  with  large  medullary  rays  are  most  liable  to  this 
injury,  oak,  beech,  walnut,  elm,  ash  and  sweet  chestnut  being  mentioned 
as  specially  susceptible  in  Europe. 

The  cracks  are  said  to  occur  most  frequently  in  the  lower  part  of  the 
trunk,  especially  where  growth  is  uneven,  as  near  roots,  at  knots  or  where 
the  stem  is  eccentric.  The  south  side,  the  region  of  most  vigorous  cir- 
cumferential growth,  suffers  most,  according  to  Fisher.  Large  old  trees 
suffer  more  than  young  because  under  conditions  inducing  this  injury 
there  is  in  the  old  trees  a  greater  difference  in  temperature  between  center 
and  periphery.  Late  winter,  when  the  sap  has  begun  to  flow,  is  said  to  be 
the  most  favorable  time  for  developments  of  this  kind.  Under  normal 
conditions  these  cracks  close  with  a  rise  in  temperature  and  the  tissues 
in  time  grow  together;  this  spot  is  weaker  however  and  subject  to  a 
recurrence  of  the  injury.  Repeated  splitting  and  healing  may  give  rise 
to  a  lipped  callus. 

Observations  in  America  agree  generally  with  Fisher's,  adding 
the  maple  to  the  list  of  subject  trees  and  finding  perhaps  more  crack- 
ing on  long,  straight-grained,  clear  boles.  Indeed  it  seems  that  the  two 
chief  reasons  for  the  comparative  resistance  of  fruit  trees  lie  in  their 
being  low  headed,  with  short  areas  of  trunk  free  from  branches  and  in 
their  smaller  trunks.  Under  cultivation  they  probably  do  not  mature  as 
early  as  forest  trees  and  the  sappy  growth  of  young  trees  may  be  injured 
in  early  winter  in  contrast  with  late  winter  for  forest  trees.  It  is  stated 
that  fruit  trees  growing  late  and  entering  the  winter  with  wood  not 
thoroughly  ripened  are  most  subject  to  frost  cracks  in  Colorado. ^^ 

On  apple  limbs  an  injury  similiar  in  appearance  and  likely  to  be 
confused  with  this  type,  sometimes  occurs  when  there  is  one  sided  develop- 
ment of  the  limb  so  that  a  heavy  load  of  fruit  is  borne  on  one  side  un- 
balanced by  any  considerable  load  on  the  other  side,  resulting  in  a  fracture 
in  a  vertical  plane.  Occasionally  after  a  nearly  horizontal  limb  is  headed 
back  to  a  large  branch  ascending  at  about  45°  a  heavy  load  on  the  ascend- 
ing branch  will  cause  a  splitting  of  the  upper  part  of  the  limb  from  the 
lower,  the  fracture  being  in  this  case  horizontal.  These  injuries  obvi- 
ously occur  near  harvest  and  should  be  differentiated  from  the  true 
"frost  cracks"  without  difficulty. 

The  reverse  of  the   conditions  described  in  connection  with  radial 


300  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

clefts,  that  is  to  say,  the  sudden  warming  of  the  outer  layers  of  the  trunk 
while  the  inside  is  still  cold,  is  said  to  produce  a  different  kind  of  injury, 
known  to  foresters  as  a  ''cup-shake."  Here  the  cleavage  instead  of 
being  in  a  radial  direction  is  along  an  annual  ring,  involving  a  smaller  or 
greater  amount  of  the  circumference.  This  form  may  possibly  occur  in 
fruit  trees  but  in  most  cases  of  separation  along  annual  rings  in  such 
plants  the  injury  may  be  traced  to  direct  killing  just  inside  the  cambium, 
discussed  under  Black  Heart.  Even  under  natural  conditions  the  cup- 
shake  is  far  less  common  than  the  frost  crack. 

In  connection  with  trunk  splitting,  the  splitting  of  the  bark  while  the 
wood  remains  intact  should  be  mentioned.  As  already  indicated  this  is 
generally  in  immature  tissues,  produced  possibly  at  times  by  the  same 
conditions  that  induce  trunk  splitting  but  more  frequently  by  the  con- 
ditions commonly  associated  with  crown  rot  and  crotch  injury.  It 
should  be  understood,  also,  that  splitting  of  the  wood  sometimes  seems 
to  be  associated  to  some  extent  with  immaturity^^  and  it  may  possibly, 
as  for  example,  when  it  occurs  during  protracted  and  intense  cold,  be  due 
to  drying  out. 

Summary. — Winter  injury  takes  many  different  aspects,  10  more  or 
less  distinct  forms  being  considered  in  this  discussion.  Many  different 
environmental  conditions  are  associated  with  winter  injury,  though  for 
convenience  these  may  be  .grouped  in  three  classes  :  (1)  conditions  encour- 
aging immaturity  of  tissues,  (2)  conditions  leading  to  winter  drought, 
(3)  conditions  leading  to  premature  quickening  in  late  winter  and  early 
spring.  Certain  sections  or  regions  are  particularly  subject  to  extremes 
of  one  kind  or  another. 

Injuries  associated  withimmaturity  are  especially  common  in  the  more 
humid  sections  with  short  growing  seasons.  Plants  adapted  to  com- 
paratively long  growing  seasons  when  taken  to  sections  with  shorter 
growing  seasons  are  particularly  subject  to  injuries  of  this  character. 
"Second  growth"  is  hkely  to  be  immature  and  subject  to  winter  injury. 
Cultural  practices  which  encourage  late  vegetative  growth  should  be 
avoided  in  regions  where  immaturity  is  a  frequent  problem.  Crown 
injury  and  crotch  injury  are  in  most  cases  associated  with  immaturity  of 
tissues  at  the  affected  points.  Wind  and  variation  in  temperature 
between  different  sides  of  the  limb  or  trunk  may  be  contributing  factors. 
Treatment  for  these  localized  injuries  should  be  both  preventive  and 
remedial. 

Injuries  due  to  winter  drought  are  especially  common  in  sections 
like  the  Dakotas  and  Wyoming  where  winter  precipitation  is  low,  the 
snow  covering  scanty  and  the  evaporating  power  of  the  air  high.  The 
tissues  are  desiccated  by  the  cold  dry  winds  and  recovery  of  turgidity 
is  difficult  or  impossible  because  of  low  soil  moisture,  deep  soil  freezing 
and  the  inability  of  the  conducting  system  to  function  while  frozen. 


WINTER  INJURY  301 

Protective  measures  include  the  use  of  winter  irrigation,  thorough 
cultivation,   frost-killed  cover  crops  and  windbreaks  or  shelter   belts. 

Many  cases  of  injury  from  cold  during  late  winter  are  associated 
with  a  breaking  of  the  rest  period,  resulting  in  some  resumption  of  growth 
and  an  accompanying  decrease  in  resistance  to  low  temperatures.  They 
are  brought  on  by  periods  of  mild  weather  during  late  winter.  Fruit 
buds  particularly  are  susceptible  to  injury  from  this  cause.  Buds  in 
certain  positions  are  especially  subject  to  this  form  of  injury.  The  ending 
of  the  rest  period  in  midwinter  or  spring  is  related  to  some  extent  to  the 
time  of  its  inception  in  the  fall.  Consequently  factors  or  practices 
which  delay  its  beginning  tend  to  protect  against  the  forms  of  winter 
inj  ury  incident  to  its  breaking.  Among  such  practices  may  be  mentioned : 
Moderatel}^  late  cultivation,  reasonably  heavy  pruning,  applications  of 
nitrogenous  fertilizers  and  thinning.  The  end  of  the  dormant  period  may 
be  delayed  somewhat  by  whitewashing  and  shading,  which  reduce  heat 
absorption. 

Most  sunscald  is  attributable  to  extreme  and  rapid  fluctuations 
in  temperature  of  the  affected  tissues.  Injuries  similar  in  appearance 
sometimes  are  caused  by  midsummer  heat  or  they  may  be  associated 
with  immaturity  coupled  with  low  temperature. 

In  general,  rapid  decreases  in  temperature  are  more  damaging  than 
more  gradual  decreases  to  the  same  or  even  to  a  lower  point.  A  special 
form  of  injury  due  to  very  rapid  temperature  decline  is  trunk  splitting 
or  frost  crack. 


CHAPTER    XVII 
WINTER  INJURY  TO  THE  ROOTS 

Root  killing  is  very  common  in  sections  where  winter  precipitation 
is  light  and  it  is  rather  common  in  humid  sections  where  it  is  not  always 
recognized.  It  may  occur,  regardless  of  precipitation,  at  any  point 
where  the  soil  freezes  at  all  deeply  (see  Table  38) ;  it  is  characteristically 
associated  with  light  and  dry  soils  and  with  scanty  snow  cover.  If 
no  part  other  than  the  roots  is  injured  the  tree  may  start  growth  in  the 
normal  way,  sending  out  vegetative  shoots  and  blossoms  and  perhaps 
even  setting  fruit;  some  time  in  the  summer,  usually  with  the  first  warm, 
dry  weather,  it  dies.  Felled  trees  will  sometimes  start  growth  in  a 
comparable  manner.  If  only  a  part  of  the  roots  have  been  injured, 
the  effect  is  quite  likely  to  be  a  slowing  in  top  growth.  As  the  damage 
is  below  ground,  it  escapes  ordinary  observation  and  the  slow  growth 
of  the  tree  may  seem  quite  inexplicable.  This  condition  may  last  for 
several  years  or  until  the  balance  between  root  and  top  is  more  nearly 
restored. 

Soil  Temperatures  in  Winter. — For  a  thorough  understanding  of  the 
nature  of  root  killing  and  of  the  conditions  associated  with  it,  some 
knowledge  of  soil  conditions  during  the  winter  and  of  the  distribution 
of  roots  in  the  soil  is  necessary.  Table  39,  taken  from  a  report  covering 
12  years  of  soil  temperature  observations  at  Lincoln,  Neb.,^^''  shows 
quantitatively  the  effect  of  depth  on  soil  temperatures. 


Table  38. — Mean  Soil  Temperatures  at  6  Inches^^" 
(Degrees  Fahrenheit) 

December 

January 

February 

March 

Pennsylvania 

Idaho             .    .    . 

34.9 
35.2 

24.1 
32.0 
33.8 
39.5 
34.0 
34.9 
57.0 

32.0 
32.1 
23.0 

22.2 
28.6 
32.0 
39.0 
27.7 
32.7 
56.1 

31.4 
32.1 
21.0 
22.7 
27.8 
32.0 
39.1 
30.4 
31.5 
57.1 

32.9 
32  9 

Minnesota 

38  0 

Wyoming 

31.0 

Nebraska 

Michigan 

Woburn,  England 

36.6 
33.5 
39.9 
36.3 

Illinois 

Alabama 

39.3 
53.4 

302 


WINTER  INJURY  TO  THE  ROOTS 


303 


The  Pennsylvania  figures  are  for  State  College,  1892-1896  inclusive;  Idaho, 
for  Moscow,  1903-1904  (Idaho  Exp.  Sta.  Bui.  49);  Minnesota,  1889  (a  mild 
winter);  Wyoming,  averages  for  Laramie,  1895,  1898,  1899;  Nebraska,  from 
Table  39;  Michigan,  selected  as  typical,  from  Mich.  Agr.  Exp.  Sta.,  Tech.  Bui. 
26,  p.  104;  Woburn,  England,  2d  Rept.,  Woburn  Experiment  Farms  (1900); 
Colorado,  Fort  Colhns;  lUinois  (Urbana),  (1897-1916);  from  Bui.  208,  111.  Agr. 
Exp,  Sta.;  Alabama,  from  Ala.  Agr.  Exp.  Sta.  Bui.  10. 

Table  40  is  arranged  from  the  same  source  and  is  introduced  to 
show  absolute  minima  at  several  depths,  over  a  series  of  years. 

Table  39. — Average  Soil  Temperatures  at  Lincoln,  Neb.is" 
(Degrees  Fahrenheit) 


Depth 

January 

February 

March 

April 

May 

June 

Air 

6  inches 

12  inches               

25.2 
28.6 
31.2 
35.4 
38.5 

24.2 
27.8 
30.2 
33.5 
35.5 

35.8 
36.6 
35.4 
35.4 
35.8 

52.1 
53.3 
49.3 
45.6 
43.8 

61.9 
65.1 
60.7 
56.2 
53.5 

71.0 
75.7 
69.9 

24  inches               

64.6 

36  inches 

61.3 

Depth 

July 

August 

September 

October 

November 

December 

.A.ir 

6  inches 

76.0 
81.6 
75.7 
70.2 
67.4 

74.5 
80.1 
75.7 
72.2 

67.6 
72.0 
69.2 
68.7 
67.6 

55.5 
57.8 
57.8 
60.0 
61.6 

38.7 
41.5 
44.7 
49.2 
,52.  2 

28.3 
32.0 

35.2 

40.1 

36  inches 

43.3 

T.\BLE  40. — Minimum  Soil  Temperatures  at  Lincoln,   Neb."" 
(Degrees  Fahrenheit) 


Winter 

6  inches 

12  inches 

24  inches 

36  inches 

1893-1894 

19.6 

24.5 

30.2 

34,2 

1894-1895 

14.9 

22.9* 

29.2* 

29.8 

1895-1896 

18.0 

27.4 

35.5 

38.0 

1896-1897 

22.0 

27.0 

33.0 

35.1 

1897-1898 

20.0 

26.5 

34.5 

36.5 

1898-1899 

7  0 

13  5 

24.0 

30.5 

1899-1900 

22.0 

28.0 

33.0 

35.0 

1900-1901 

24.0 

28.0 

34.0 

36.0 

1901-1902 

19.0 

27.0 

33.0 

35.0 

Data  incomplete. 


The  maximum  depth  of  frost  penetration  at  the  same  point  has  been 
reported  as  detailed  in  Table  41.     Recently,  however,  it  has  been  shown 


304  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Table  41. — Maximum  Depth  of  Frost  Penetration  at  Lincoln,  Neb. 


Date 

Depth, 
inches 

Date 

Depth, 
inches 

Mar  9  1891 

30.9 

21.9 

32.2 

29.0 

36.0* 

18.4 

Jan  19  1897         

21.2 

Jan  19  1892 

Feb.  8,  1898      

16.8 

Feb  12  1893 

Feb.  10  to  Mar.  28,  1899 

Feb. 29,  1900 

Feb.  12,  1901 

36.0 

Feb  27  1894       

21.6 

Feb  7-27  1895  

20.0 

Jan  4,  1896    

Feb.  9,  1902 

21.6 

*  Not  recorded  to  maximum  penetration. 

that  soil  does  not  freeze  until  it  is  cooled  several  degrees  below  32°F.2s 
Consequently  since  these  figures  were  based  on  the  assumption  of  freezing 
at  32°  the  actual  frost  penetration  was  not  so  great  as  is  indicated. 

Critical  Temperatures  for  Tree  Roots. — In  the  section  on  Water 
Relations  the  extent  and  the  depth  of  some  fruit  tree  root  systems  are 
indicated.  The  data  there  given  indicate  that  in  the  majority  of  fruit 
growing  regions  by  far  the  greater  part  of  the  feeding  roots  is  in  the 
surface  foot  of  soil. 

The  finer  roots  of  beech,  oak  and  ash,  trees  that  are  considered 
at  least  fairly  hardy,  die  at  temperatures  between  8.6°  to  3.2°F.i"  and  the 
roots  of  other  hardy  plants  are  reported  killed  at  temperatures  from 
14°  to  5°F.^^  Working  with  apple  roots,  under  laboratory  conditions, 
Chandler  found  that  "the  killing  temperature  varies  from  —  3°C.  in 
summer  to  about  -12°C.  [26.6°F.  to  10.4°F.]  in  late  winter  with  rather 
rapid  freezing."  He  remarks  further,  "They  are  still  very  tender  in 
autumn  when  tissue  above  ground  has  begun  to  increase  rapidly  in  hardi- 
ness ...  as  the  roots  extend  away  from  the  crown  they  become  more 
and  more  tender  and  apparently  this  tenderness  is  greater  on  those  roots 
that  extend  downward  into  the  soil."  It  may,  then,  be  concluded  that 
the  roots  of  most  plants  are  more  tender,  at  a  given  temperature,  than  the 
parts  above  ground.  Parentheticall,y,  though  Chandler's  statement 
as  to  increasing  tenderness  with  increasing  distance  from  the  crown  may 
be  accepted,  it  should  be  understood  that  root  killing  is  frequently 
observed  at  or  near  the  crown  and  not  elsewhere,  probably  because  this 
part  is  nearest  the  top  soil  and  therefore  exposed  to  colder  temperatures, 
as  shown  in  Table  39. 

Carrick^^  found  a  marked  difference  in  tenderness  of  roots  at  different  seasons 
in  New  York.  "The  material  frozen  in  October  and  November,"  he  states, 
"shows  a  marked  tenderness  compared  with  roots  tested  in  February  and  March. 
The  period  of  maximum  resistance  seems  to  end  somewhat  before  the  last  of 
March,  tho  the  date  would,  of  course,  vary  with  the  conditions  affecting 
after-ripening  and  possibly  also  with  the  variety  .  .  .  This  range  of  hardiness 
indicates  a  difference  in  resistance  of  between  3  and  4  Centigrade  degrees. 


WINTER  INJURY  TO  THE  ROOTS  305 

These  seasonal  differences  obtain,  not  only  in  the  apple  seedlings,  but  in  all  the 
roots  reported  in  this  paper." 

Another  interesting  factor  in  root  injury  is  reported  by  Carrick,  He  finds 
that,  "the  resistance  is  in  direct  proportion  to  the  diameter  of  the  root,"  and 
suggests  that  this  fact  accounts  for  the  occasional  observation  in  laboratory 
freezings  of  root  killing  at  the  tips  when  the  roots  near  the  crown  are  uninjured. 

A  study  of  Table  38,  with  the  killing  temperatures  given  above  in 
mind,  shows  that  the  average  soil  temperatures  in  the  recognized  fruit 
growing  sections  noted  are  substantially  above  the  danger  point  and 
suggests  one  reason  why  fruit  growing  in  certain  other  sections  requires 
some  special  precautions.  Attention  is  due,  further,  to  the  consideration 
that  these  are  average  figures  in  which  fluctuations  to  lower  points  are 
submerged.  In  Table  40  the  actual  seasonal  minimum  temperatures  at 
one  point  are  segregated.  It  is  particularly  significant  that  the  winter  of 
1898-1899,  when  the  soil  temperature  at  Lincoln,  Neb.,  reached  7°r.,  was 
the  winter  characterized  by  an  extreme  amount  of  root  killing  in  lowa,^"^ 
Wisconsin^''  and  Ontario."^ 

Factors  Influencing  Frost  Penetration. — Temperature  alone,  or  air 
temperature  alone  certainly,  is  not  the  sole  controlling  factor  in  root 
killing.  A  temperature  of  —  20°F.  maintained  for  several  days  has 
caused  extensive  root  killing  in  Ontario.^"  Goff"  in  an  interesting  survey 
of  an  extensive  area  involved  in  the  freeze  of  February,  1899,  found  little 
damage  in  several  regions  where  the  unofficial  temperatures  went  as  low 
as  —  50°  or  even  —  52°F.,  though  in  no  case  where  root  killing  occurred 
had  the  temperature  gone  below  —  36°F.  A  report  from  Waukee,  Iowa, 
indicated  root  killing  with  a  minimum  of  —  24*'F. ;  other  localities  suffered 
severely  at  —  23°F. 

Protection  Afforded  by  Snow. — The  principal  difference  lay  in  the 
fact  that  in  some  sections  snow  lay  on  the  ground  while  in  others  there 
was  none.  Goff's  analysis  showed  34  localities  with  more  or  less  snow 
at  the  time  of  the  freeze;  of  these,  20  reported  definitely  that  the  chief 
injury  was  in  the  tops,  three  reported  roots  and  tops  equally  damaged, 
while  in  one  there  was  more  injury  to  roots  than  to  tops  in  apples  but 
more  in  the  tops  of  cherries  and  plums  than  in  the  roots.  Fifty-seven 
localities  were  without  snow  at  the  time  of  the  freeze;  definite  statements 
of  comparative  injury  indicated  43  cases  where  the  principal  damage  was 
in  the  roots,  3  placed  it  in  the  tops  and  1  reported  roots  and  tops 
equally  damaged. 

Similar  testimonials  concerning  the  value  of  a  snow  covering  are 
common  in  pomological  literature.  Quantitative  data  applicable  here 
are  given  by  Bouyoucos."  Table  42,  arranged  from  his  figures  taken  at  a 
depth  of  3  inches,  shows  the  temperature  differences  between  ground 
without  snow,  ground  under  compacted  snow,  under  uncompacted  snow 
and  under  vegetation  plus  compacted  snow. 


306 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Table  42. — Effect  of  Snow 

Cover  on  Soil.  Temperature,  January, 

1915" 

(Degrees  Fahrenheit) 

Maximum-minimum 

Air 

Monthly  average 

Bare 

Snow, 
compact 

Uncom- 
pact 

Uncom- 

pact    + 

vegetation 

Maxi- 
mum 

Mini- 
mum 

Average 

28.79 

24.95 

3.84 

29.65 
28.66 
0.99 

31.51 
31.11 
0.40 

34.82 
34.55 
0.27 

27.96 

13.80 

20.64 

^           „     /  niaxuuum 

Jan.     6,    < 

1  minimum 

32.30 

32.00 

32.00 

35.70 



32.10 

31.80 

32.00 

35.50 

39.00 

33.00 

36.00 

Jan.  29,    /  m^xunum 

'  "   '    \  minimum 

20.00 

22.30 

29.60 

33.00 



14.50 

20.80 

29.00 

32.50 

13.00 

-13.00 

0.00 

Jan,  30.   I"^™"-" 

[  minimum 

21.20 

21.  10 

28.80 

32.80 

7.50 

15.60 

27.00   '        32.30 

18.00     -13.00 

2.00 

The  minimum  for  Jan.  30  is  certainly  at  tiie  danger  point  for  tree  roots 
in  bare  ground,  while  under  compacted  snow  it  is  8.1°F.  higher  and  under 
vegetation  plus  compacted  snow  it  is  almost  25°  higher.  The  fruit 
grower  cannot  induce  snowfall  at  his  will  but  he  sometimes  has  a  choice 
between  a  slope  where  snow  will  remain  and  one  where  it  will  melt  away 
with  a  little  warm  weather.  He  knows  that  knolls  and  wind  swept  spots 
in  general  are  likely  to  need  special  care  and  that  cover  crops  and  wind- 
breaks tend  to  hold  snow  that  might  otherwise  blow  away. 

Different  Systems  of  Soil  Management. — A  protective  covering  of 
vegetation  can  be  provided  by  the  grower  with  more  surety  than  a  snow 
covering.  Table  43,  arranged  from  data  by  Bouyoucos,^^  shows  the 
effect  of  this  covering  on  minimum  soil  temperatures  at  3  inches  depth. 
The  superior  protection  afforded  by  cultivated,  bare  soil  as  contrasted 
with  compacted  soil  is  worthy  of  note. 

Table  43. — Average  Minimum  Soil  Temperatures  in  Uncultivated  and  Culti- 
vated Soil  and  in  Sod^^ 
(Degrees  Fahrenheit) 


Month 

Uncultivated 
(bare) 

Cultivated 
(bare) 

Sod 

Dec,  1914 

Jan.,  1915 

Feb.    1915. 

31.92 
31.11 
30.70 

33.26 
32.59 
32.49 

35.34 
34.55 
33.52 

Craig^^  in  Iowa  reported  soil  temperature  at  6  inches  depth  on  a 
January  day,  after  hard  freezing,  two  degrees  warmer  in  sod  than  in 
cultivated  soil. 

Depth  of  freezing  is  a  fairly  good  indicator,  though  indirect,  of  soil 
temperature.     Gourley^^  records  observations  made  in  New  Hampshire 


WINTER  INJURY  TO  THE  ROOTS  307 

in  March  when  freezing  was  at  its  greatest  depth  for  the  season;  these 
are  shown  in  Table  44.  These  figures  are  of  special  interest  since  they 
show  the  protective  effect  of  increased  cover-crop  growth  induced  by 
fertilizer  applications.  The  "cultivated  with  cover  crop"  plot  had  a 
scanty  growth. 

Table  44. — Depth  of  Freezing  as  Affected  by  Soil  Covering 

Clean  cultivated  (no  cover  crop) 16  inches 

Cultivated,  with  cover  crop 15  inches 

Sod 12  inches 

Fertilizer,  cultivation  and  cover  crop 10  inches 

Fertilizer  (excess  nitrogen)  cultivation  and  cover  crop.  .  .  7  inches 


Sandsten^^^  made  measurements  of  the  depth  of  frost  penetration  in 
early  February  under  different  crops  in  Wisconsin.     Table  45  shows  his 

Table  45. — Frost  Penetration  under  Different  Cover  Cropsi^^ 

Bluegrass  sod 18.0  inches 

Clean  cultivation  (no  cover  crop) 16.0  inches 

Rape 15.0  inches 

Oats 8.0  inches 

Hairy  vetch 7.5  inches 

data.  He  interprets  these  observations  to  emphasize  the  protective 
value  of  an  uncompacted  cover,  the  bluegrass  sod  offering  httle  insulation 
because  of  the  lack  of  dead  air  spaces.  He  also  considers  the  lower 
amount  of  moisture  in  sod  land  to  have  an  important  bearing.  In 
connection  with  the  data  here  cited  from  Gourley  and  from  Sandsten  it 
should  be  recalled  that  the  soil  does  not  freeze  until  its  temperature  is 
several  degrees  below  32°F. 

Oskamp'^2  reports  soil  temperatures  observed  in  Indiana  with  differ- 
ent soil  covers.     Table  46  is  arranged  from  his  data.     It  should  be  noted 

Table  46. — Monthly  Minimum  Soil  Temperatures"* 
(Degrees  Fahrenheit) 


Clean  cultivation 
and  cov«r  crop 

Straw  mulch 

Jan.,  1915 

31.0 

34.0 

Feb.,  1915 

32.0 

34.0 

Dec, 1915 

32.5 

38.0 

Jan.,  1916 

28.5 

35.0 

Feb.,  1916 

32.0 

35.0 

Dec, 1916 

33.0 

35.0 

that  this  comparison  is  between  straw  mulch  and  land  growing  a  cover 
crop,  which  has  been  shown  to  have  higher  minimum  temperatures  than 


308 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


uncultivated  or  cultivated  bare  land  or  sod.  A  direct  comparison  of  the 
extremes  is  not  available,  but  by  comparing  minimum  temperatures  in 
bare  land  with  those  in  sod  (Tables  43  and  44),  then  sod  with  cover  crop 
(Tables  44  and  45)  and  finally  cover  crop  with  straw  mulch,  some  idea  of 
the  superior  protective  qualities  of  the  straw  mulch  can  be  formed.  As 
will  appear  later,  the  difference  between  safe  and  killing  temperatures  for 
roots  is  slight  and  a  few  degrees  are  apparently  more  important  below 
ground  than  above. 

Soil  Type. — Increased  injury  in  sandy  soil  has  been  reported  so 
frequently  that  the  precise  temperature  conditions  existing  in  the  lighter 
soils  should  be  examined  carefully.  Table  47  shows  absolute  minimum 
temperatures  for  certain  months,  recorded  at  a  depth  of  six  inches,  in 
soils  of  different  types. 


Table  47. — Absolute  Minimum  Temperatures  in  Different  Soils 

{After  Bouyoucos'^^) 
(Degrees  Fahrenheit) 


Gravel 

Sand 

Loam 

Clay 

Peat 

Dec,  1912 

Jan.,  1913 

Feb.,  1913 

Dec,  1914 

29.0 
30.8 
21.1 
30.0 
30.5 
32.1 

28.9 

29.7 
29.1 
17.3 
25.3 
27.1 
32.4 

26.8 

30.3 
30.9 
22  3 
31.5 
31.4 
31.3 

29.6 

30.2 
31.2 
23.1 
30.3 
32.0 
31.9 

29.8 

31.4 
31.1 
19.1 
32.6 

Jan.,  1915 

Feb.,  1915 

32.4 
32.2 

Average 

29.8 

These  figures  show  a  sufficient  difference  to  indicate  a  possible  cause 
for  increased  root  killing  in  sandy  soils.  It  should  be  stated,  however, 
that  Bouyoucos  records  a  very  marked  tendency  for  all  soils  to  assume 
a  uniform  temperature  if  air  temperatures  remain  stable  long.  The 
lower  minima  in  sand  are  due  probably  to  more  rapid  conductivity  so 
that  a  cold  spell  of  short  duration,  as  most  cold  waves  are,  would  take 
effect  here  but  be  over  before  it  would  affect  some  of  the  other  soils  to 
the  same  extent.  Thus,  Bouyoucos  states,  ''The  12-inch  depth  of 
gravel  and  sand  froze  Feb.  3,  that  of  loam,  clay  and  peat  on  Feb.  5,  or 
2  days  later;  while  the  18-inch  depth  of  the  various  soils  froze  as  follows: 
gravel,  Feb.  6,  sand,  Feb.  8,  clay,  Feb.  10,  loam,  Feb.  1 1 ,  that  of  peat  did  not 
completely  freeze,  its  temperature  remaining  a  few  tenths  of  a  degree 
above  32°F.  throughout  the  rest  of  the  winter."  As  to  the  effect  of 
organic  matter  in  soil,  he  comments  on  his  investigations  as  follows: 
"The  minimum  temperature  attained  was  highest  in  peat,  slightly  less 
and  about  the  same  in  the  various  soils  treated  with  peat  and  lowest  in 


WINTER  INJURY  TO  THE  ROOTS 


309 


the  untreated  sand."  A  continued  turning  under  in  the  spring  of  cover 
crops  tends  to  raise  the  soil  content  of  organic  matter.  The  cover  crop 
protects,  then,  while  above  ground  by  blanketing  the  soil  and  when 
turned  under  it  affords  some  protection  in  the  following  winter  through 
the  increased  amount  of  organic  matter  it  has  supplied. 

Soil  Moisture. — Another  factor,  possibly  of  equal  importance,  affect- 
ing root-killing  in  sandy  soils,  is  the  amount  of  moisture  present.  No 
evidence  need  be  introduced  here  as  to  the  comparatively  low  moisture 
content  of  the  average  sandy  soil.  Emerson^^  made  some  very  interest- 
ing studies  of  the  effects  of  moisture  on  killing,  in  which  lots  of  25 
young  trees  each  were  exposed  to  a  Nebraska  winter,  in  boxes  of  loam 
soil  with  varying  degrees  of  moisture.  His  tabular  statement  of  results 
is  reproduced  here  as  Table  48. 


Table  48.— Root-killing  of  Apple  Seedlings  as 

Related  to  Soil  Moisture 

Percent- 

Number of  roots 

Box 

Where  kept 

Soil  cover 

age  of  soil 

moisture 

Uninjured 

Injured 

Dead 

1 

Outdoors 

None 

10.4 

0 

5 

20 

2 

Outdoors 

None 

15.2 

0 

6 

10 

3 

Outdoors 

None 

19.8 

12 

10 

3 

4 

Outdoors 

None 

25.6 

13 

4 

8 

5 

Outdoors 

Straw  mulch 

16.0 

18 

7 

0 

6 

Outdoors 

Snow  occasionally 

15.8 

10 

8 

7 

7 

Cool,  dry  cave 

None 

10.0 

25 

0 

0 

Emerson  comments  on  his  results  in  part  as  follows:  "That  the  great  injury 
to  the  seedling  roots  in  the  drier  soils  is  not  due  directly  to  the  dryness  alone  but 
to  dryness  and  cold  combined,  is  evident  from  the  fact  that  the  roots  were 
absolutely  unhurt  in  equally  dry  soil  kept  in  a  cool  dry  cave.  .  .  .  That  dry- 
ness alone  was  not  responsible  is  shown  by  the  comparatively  slight  injury  to 
roots  in  rather  dry  soil  which  was  protected  by  a  4-inch  mulch  of  straw,  while 
roots  in  bare  soil  of  almost  the  same  moisture  content  were  very  badly  hurt. 

"Just  why  severe  freezing  should  injure  roots  worse  in  rather  dry  than  in 
moist  soil  is  not  shown  by  the  test  reported  above.  On  further  investigation  it 
may  be  found  that  roots  are  simply  unable  to  withstand  severe  freezing  or  to 
recover  from  it  unless  surrounded  by  an  abundance  of  moisture.  Be  this  as  it 
may,  it  is  quite  probable  that  one  cause  of  the  great  injury  in  rather  dry  soil  is 
alternate  freezing  and  thawing  .  .  .  the  more  water  a  soil  contains  the  less 
subject  it  is  to  frequent  alternate  freezing  and  thawing. 

"The  fact  that  the  apple  seedlings  were  much  less  seriously  injured  where 
protected  by  a  mulch  of  straw  than  they  were  in  bare  ground  is  to  be  explained 
by  the  effect  of  mulches  on  freezing  and  thawing  of  the  ground.  The  latter  was 
tested  during  the  winter  of  1901-1902.     The  mulch  protected  the  soil  not  only 


310 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


against  severe  freezing  during  cold  nights,  but  also  against  alternate  freezing 
and  thawing.  The  temperature  changes  observed  on  February  2,  3  and  4, 
1902 — a  very  cold  period — are  especially  interesting.  The  surface  of  the  bare 
ground  thawed  during  the  middle  of  the  day  and  froze  severely  each  night.  Two 
inches  lower,  however,  the  soil  did  not  thaw  out  during  this  very  cold  weather, 
though  the  temperature  changes  between  day  and  night  were  great.  The 
temperature  of  the  mulched  ground,  both  at  the  surface  and  2  inches  beneath 
it,  remained  constantly  below  the  freezing  point  and,  moreover,  varied  but  little 
during  the  period." 

Recent  studies  by  Bouyoucos^*  suggest  an  interesting  possibility  in 
this  connection.     He  shows  that  in  practically  all  agricultural  soils  some 
of  the  moisture  remains  unfrozen  at  ordi- 
nary temperatures  and,   indeed,    even   at 

—  78°C.  The  amount  of  unfrozen  water 
varies  with  the  kind  of  soil,  becoming  in 
general  greater  as  the  soils  vary  from  the 
simple  and  non-colloidal  to  the  complex 
and    colloidal.     The    amount   freezing   at 

—  78°C.  is  very  little,  if  any,  greater  than 
that  freezing  at  —  4°C.  It  seems  possible, 
then,  that  the  increased  amount  of  root 
injury  in  sandy  soils  may  be  due,  in  ad- 
dition to  the  lower  amount  of  moisture  in 
such  soils,  as  mentioned  above,  to  the  ex- 
tremely small  amount  of  water  remaining 
unfrozen  at  temperatures  only  slightly 
below  0°C.  while  the  finer  soils  have  a 
reserve  of  capillary  adsorbed  unfrozen 
water  under  such  circumstances. 

It  should  also  be  recognized  that  temperatures  in  the  different  soils 
may  have  been  different.  In  any  case,  however,  the  result  is  the  same; 
damage  is  greater  in  soils  that  are  dry  at  the  time  of  freezing. 

Relation  of  Cover  Crops  to  Root  Killing. — The  effects  of  single  factors 
on  soil  temperatures,  and  therefore  on  root  killing,  have  been  set  forth. 
The  value  of  a  snow  cover  has  been  shown;  the  increase  of  soil  tempera- 
tures with  transition  from  bare  ground  through  sod  to  cover  crops  has 
been  reviewed ;  minima  varying  with  the  character  of  the  soil  have  been 
indicated  and  finally  dryness  of  soil  has  been  shown  to  be  associated 
with  root  killing.  In  orchard  practice,  however,  these  factors  are  rarely 
operative  singly  and  some  rather  complicated  interactions  may  be 
expected. 

Emerson's^^  studies  on  depth  of  freezing  under  two  sets  of  conditions 
are  of  great  importance  since  they  show  the  interactions  referred  to  above. 
Figures  30  and  31,  reproduced  from  his  studies,  indicate  depth  of  freezing 


Fig.  30. — Depth  of  freezing 
under  various  covers,  in  absence 
of  snow.      (After  Emerson^^) 


WINTER  INJURY  TO  THE  ROOTS 


311 


without  snow  covering  and  with  snow  covering  respectively.  Under  both 
sets  of  conditions  the  clean  cultivated  land  froze  deepest.  More  striking, 
however,  is  the  different  position  occupied  by  the  corn  plot  under  different 
conditions.  The  reason  becomes  apparent,  however,  when  the  depth  of 
snow  covering  on  the  several  plots  is  considered.  The  close  relation 
between  depth  of  snow  and  depth  of  freezing,  shown  in  all  plots,  is  of 
interest. 


Fig.  31. — Relation  of  cover   crops   to   depth  of  snow  and   depth  of  frozen  soil. 


(After 


Emerson's  observations  furnish  more  information:  "Early  in  the 
winter  ...  it  was  noted  that  soy  beans  had  very  few  leaves  left  and 
that  the  plants  stood  perfectly  erect,  furnishing  almost  no  protection  to 
the  soil  and  that  cowpeas,  tho  they  still  held  their  leaves,  stood  too 
erect  to  furnish  much  protection.  The  field  peas,  on  the  other  hand,  had 
held  their  leaves  well  and  matted  down  nicely,  forming  a  very  good  mulch. 
Corn  was  also  found  to  have  remained  very  erect  as  was  also  the  case  with 
cane  and  millet.  Later  in  winter  it  was  noted  that  the  snow  was  held 
very  well  by  corn,  cane,  millet,  soy  beans  and  cowpeas,  while  field  peas 
and  rye,  the  good  covers,  laid  too  flat  on  the  ground  to  catch  the 
drifting  snow.  The  almost  bare  stems  of  such  plants  as  soy  beans,  which 
still  stood  erect,  held  the  snow  much  better  than  a  plant  like  field  peas 


312  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

which  retained  its  leaves  but  matted  down  too  close  upon  the  ground. 
The  stalks  left  standing  after  a  crop  of  corn  grown  in  the  ordinary  way  has 
been  harvested  make  a  very  efficient  snow  holder  but  furnish  very  little 
protection  to  the  ground  at  times  of  intense  cold  unaccompanied  by 
snow." 

The  superior  snow-retaining  qualities  mentioned,  particularly  in  the 
case  of  corn,  are  operative  mainly  when  the  snow  fall  is  accompanied  by 
wind. 

Summarizing  the  requirements  for  a  cover  crop  under  Nebraska 
winter  conditions,  Emerson  says:  "It  should  start  growth  promptly  in 
order  to  insure  an  even  stand  and  to  choke  out  weeds.  It  should  grow 
vigorously  to  insure  a  heavy  winter  cover  and  to  dry  the  ground  in  case 
of  late-growing  trees  so  as  to  hasten  their  maturity.  It  should  be  killed 
by  the  early  frosts  so  that  it  will  stop  drying  the  ground  after  danger  of 
late  tree  growth  is  passed  and  help  to  conserve  our  light  rains  so  much 
needed  by  the  trees  in  winter.  ...  A  cover  crop  should  be  heavy 
enough  to  furnish  as  good  direct  protection  as  possible  against  freezing 
and  thawing  and  it  should  stand  sufficiently  erect  to  hold  snow  against 
the  power  of  strong  winds." 

Of  the  crops  tried,  that  which  appeared  to  come  nearest  meeting  these 
requirements  in  Nebraska  was  German  millet. 

Root  Killing  in  Different  Fruits. — There  is  less  latitude  in  the  root 
hardiness  of  the  various  species  than  in  the  hardiness  of  their  tops. 
Nevertheless  there  are  enough  differences  in  many  cases  to  make  the 
choice  of  root  stocks  very  important. 

The  Apple. — Carrick^^  found  that  the  majority  of  dormant  apple  roots 
were  seriously  injured  at  a  temperature  of  —  12°C.,  with  considerable 
injury  at  —  7°C.  He  reports  the  cambium  as  the  most  tender  tissue, 
followed  closely  by  the  phloem,  with  the  cortex  less  tender.  Under 
extreme  conditions  xylem  and  pith  are  said  to  be  killed.  French-grown 
stocks  were  found  substantially  as  hardy  as  the  native-grown  seedlings. 
In  all  cases  there  was  a  considerable  variation,  as  would  be  expected 
among  seedling  plants.  This  difference,  it  may  be  remarked,  is  likely 
to  assume  considerable  importance  under  field  conditions. 

The  Pear. — Studies  on  pear  roots  by  the  same  investigator  indicated 
that  Kieffer  roots  were  more  resistant  than  the  French  stock.  A  tem- 
perature of  —  11°C.  during  the  dormant  period  produced  extensive  injury 
in  both.  In  April  Kieffer  showed  only  slight  injury  at  —  9°C.  while  2-year 
French  roots  were  killed.  Pear  roots  seemed  to  acquire  hardiness  later 
than  those  of  the  apple  and  never  become  quite  so  hardy. 

The  Peach. — The  peach  root  is  relatively  hardier  in  the  zone  of  dis- 
tribution of  this  species  than  is  the  apple  root  along  the  northern  border 
of  apple  growing.  Occasionally,  however,  root  killing  in  peaches  occurs. 
Goff^®  records  that  in  the  freeze  of  1899  peach  tops  suffei;ed  more  than  the 


WINTER  INJURY  TO  THE  ROOTS  313 

roots;  Green  and  Ballou^^  indicate  peach  root  killing  in  Ohio.  Macoun^^^ 
reports  similar  injury  to  thousands  of  peach  trees  in  southern  Ontario 
in  the  winter  of  1898-1899.  However,  root  killing  without  any  appreci- 
able amount  of  injury  to  the  top,  as  occurs  from  time  to  time  in  the  apple, 
is  extremely  rare  in  the  peach;  conditions  severe  enough  to  injure  peach 
roots  generally  will  work  far  greater  damage  to  the  tops. 

Carrick^^  summarizes  the  results  of  laboratory  freezing  of  peach  roots  as 
follows:  "As  a  general  rule  the  order  of  resistance  of  the  various  tissues  in  the 
peach  root  seems  to  be  as  follows:  pith,  cortex,  phloem,  cambium,  xylem.  At 
—  18°C.  or  below,  the  xylem  was  usually  killed  during  the  hardiest  period.  In 
most  cases  during  February  and  March  the  pith  is  the  tissue  most  easily  killed, 
but  in  April  the  cambium  is  the  least  resistant. 

"It  is  not  so  easy,  with  the  data  at  hand,  to  assign  an  arbitrary  hmit  within 
which  the  peach  root  is  injured  by  freezing.  This  is  because  of  the  great  varia- 
tion in  the  root  tissues.  The  peach  cambium  certainly  is  as  hardy  as  the  pear 
cambium,  tho  less  so  than  the  apple.  Regardless  of  the  size  of  the  root,  most 
of  the  peach  material  tested  showed  some  injury  at  —  10°C.,  and,  except  in 
unusual  cases,  serious  injury  occurred  at  —11°.  This  would  then  place  the 
hardiness  of  the  peach  root  very  close  to  that  of  either  pear  seedHng." 

The  Cherry. — Sour  cherries  frequently  suffer  from  root  killing  on  the 
northern  margin  of  their  range,  sometimes  under  conditions  such  that  the 
top  is  uninjured.  Hansen*^  states:  "One  great  difficulty  in  cherry  grow- 
ing in  this  state  is  the  tender  imported  Mahaleb  and  Mazzard  stocks  upon 
which  we  are  compelled  to  bud  and  graft  at  present.  These  root-kill  in 
severe  winters."  Under  some  conditions  the  flower  buds  of  sour  cherry 
may  be  more  resistant  than  the  roots.  Craig^^  reported  on  damage  to 
cherry  stocks  in  Iowa  in  1898-1.899:  "In  nursery,  the  former  [Mazzard] 
was  practically  a  total  loss  of  2-year-olds  and  a  complete  loss  of  1-year-old 
in  the  region  of  the  severe  root  killing.  Mahaleb  suffered  less,  Morello 
stock  and  own-rooted  Morello  trees  generally  escaped  with  slight  injury, 
except  in  exposed  situations.  ...  In  the  college  nurseries  the  practice 
of  root  grafting  the  cherry  received  commendation  by  the  fact  that  the 
only  trees  which  escaped  were  those  which  were  partly  on  their  own  roots." 
Prunus  pennsylva7iica  is  reported  from  several  sources  to  be  hardy  but  is 
difficult  to  work  commercially. 

Carrick^^  places  the  relative  hardiness  in  cherry  stocks  in  descending 
order  as  follows:  Mahaleb,  Prunus  Besseyi,  Prunus  yennsylvanica, 
Mazzard  and  he  finds  the  Mahaleb  generally  much  hardier  than  the  apple 
roots  investigated.  "In  large  Mahaleb  roots  during  their  hardiest 
period,"  he  states,  "little  injury  is  found  under  —  14°C.,  while  at  — 15° the 
injury  is  relatively  small.  .  .  .  The  Mazzard  roots  in  no  instance  with- 
stood — 11°,  but  the  number  of  tests  run  at  —  10°  was  insufficient  to  place 
this  as  its  minimum.  From  these  results  the  Mazzard  cherry  stock  does 
not  appear  hardier  than  Keiffer  pear  stock." 


314  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

The  Plum. — Iowa's  experience  with  plums  in  the  winter  1898-1899  is 
thus  stated  by  Craig :^^  "Plums,  native  or  European,  worked  on  peach 
or  Myrobolan  killed,  on  Marianna  badly  injured,  on  Americana  slightly 
injured,  but  these  recovered  rapidly  except  where  they  were,  in  a  few 
instances,  permanently  inj  ured ....  Americanas  worked  on  peach  roots 
escaped  where  well  rooted  from  the  cion.  Sand  cherry  stock  (Prunus Bes- 
seyi)  has  been  used  to  some  extent  in  the  state.  In  no  case  have  I  found 
these  roots  injured  in  the  slightest  degree.  In  passing  I  may  add  that  ex- 
perience has  not  yet  developed  the  ultimate  effect  of  this  stock  upon  the  cion. 
Thus  far  its  dwarfing  influence  upon  varieties  of  the  Americana  type  is 
satisfactorily  demonstrated.  Domestica  plums  on  own  roots  fared  better 
than  the  same  varieties  on  peach,  Myrobolan  or  Marianna."  Elsewhere: 
"On  the  matter  of  plums  the  sand  cherry  {Prunus  Besseyi)  appears  to  be 
the  hardiest  form  we  know  anything  about.  Native  plums  in  the  college 
orchard  on  this  stock  were  entirely  uninjured  last  winter,  while  the  same 
varieties  on  Americana  stocks  alongside  were  injured  or  killed."  Carrick 
places  Myrobolan  in  the  same  group  as  Mazzard  cherry  and  pear  for 
hardiness. 

The  Grape. — Reports  of  root  killing  in  grapes  are  relatively  rare.  The 
comparatively  deep-rooting  habit,  combined  with  sufficient  tenderness  of 
tops  to  discourage  grape  growing  in  regions  where  root  killing  is  common, 
may  account  for  this  apparent  resistance.  Furthermore,  most  grapes 
of  American  origin  are  in  fact  hardy  varieties  on  their  own  roots  and  if  it 
be  safe  to  reason  from  the  analogy  of  cion-rooted  trees,  the  roots  should 
share  the  hardiness  of  the  tops.  Niagara  has  been  reported  to  be  notor- 
iously tender  in  bud  and  root.^*  Hansen^^  reports  considerable  trouble  in 
parts  of  South  Dakota  from  root  killing;  the  New  York  vineyards  suffered 
extensive  damage  in  the  winter  of  1903-1904.  Hedrick^-  suggests  that 
the  St.  George  (a  variety  of  rupestris)  stock  used  in  some  experimental 
work  at  Geneva,  N.  Y.,  may  be  more  hardy  than  certain  others  and  notes 
that  American  varieties  on  their  own  roots  winter  killed  extensively. 

Carrick  made  numerous  laboratory  freezings  of  six  varieties  of  grapes  to 
compare  their  relative  hardiness.  The  varieties  studied,  representing  several 
species,  fell  readily  into  two  classes,  viz.,  Clinton,  Concord  and  Diamond,  "rather 
resistant  to  cold"  and  Cynthiana,  Lindley  and  Norton,  "relatively  easy  to  kill 
by  freezing."  Within  the  groups  the  differences  in  hardiness  are  not  striking. 
For  the  hardier  group,  "Only  scattering  injury  is  recorded  at  —11°,  —12°,  and 
—  13°C.  At  an  exposure  of  —14.5°,  22  out  of  27  Concord  roots  were  uninjured, 
and  only  a  trace  of  cambium  and  cortex  injury  was  noted  in  the  remainder. 
...  At  —18°,  however,  the  cambium,  phloem,  and  cortex  tissues  were  com- 
pletely injured  in  all  roots,  with  some  xylem  injury  in  the  Diamond  and  the 
Concord.  .  .  .  The  limits  of  this  second  group  (Cynthiana,  Lindley  and 
Norton)  he  between  —10°  and  —  12°C.,  the  roots  usually  undergoing  con- 
siderable injury    at    —11°.     In  relative  hardiness    this  places  these  varieties 


WINTER  INJURY  TO  THE  ROOTS  315 

between  the  Mazzard  cherry  and  the  apple.  The  Chnton,  Concord,  and  Dia- 
mond roots,  even  excluding  the  influence  of  size,  are  considerably  more  resistant 
than  apple  roots,  and  Concord  and  Clinton  seem  equal  if  not  superior  to  the 
Mahaleb  stock. 

"  .  .  .  Vitis  (Bstivalis,  represented  by  Norton  and  Cynthiana,  is  not  adapted 
to  severe  cold,  and  this  may  account  for  the  fact  that  its  range  is  limited  to  the 
South.  The  tenderness  of  Lindley  is  probably  due  in  part  to  the  influence  of 
Vitis  vinifera,  which,  as  is  well  known,  will  not  survive  the  winter  in  the  latitude 
of  New  York  State  without  much  protection.  Concord  and  Diamond  represent 
Vitis  labrusca,  the  Northern  Fox  grape,  which,  while  restricted  in  distribution,  is 
found  in  Maine.  Vitis  vuljmia,  represented  by  Clinton — a  variety  with  extremely 
resistant  roots — has  the  greatest  range  of  any  American  species  of  grape,  it 
having  been  found  in  Canada  north  of  Quebec. "^^ 

The  Sfnall  Fruits. — Among  small  fruits  Carrick  found  a  wide  range 
in  hardiness.  The  blackberry,  dewberry  and  red  raspberry  roots  tested 
appeared  to  rank  with  the  IMyrobolan  plum  and  the  Mazzard  cherry. 
Eldorado  seemed  the  hardiest  of  the  blackberries  under  observation,  but, 
curiously  enough  the  Lucretia  dewberry  seemed  somewhat  more  hardy 
than  Eldorado.  The  roots  of  the  Cuthbert  raspberry  appeared  equal  in 
hardiness  to  the  Eldorado  blackberry.  None  of  the  varieties  studied 
survived  a  temperature  of  —  12°C.,  though  many  of  the  larger  roots  were 
uninjured  at  —  11°C.  On  the  other  hand,  currant  and  gooseberry  roots 
were  extremely  resistant;  a  Downing  gooseberry  root  withstanding 
—  20.5°C.,  though  this  probably  would  be  the  limit  of  hardiness.  On  the 
basis  of  the  material  examined  Carrick  rather  provisionally  rates  the 
gooseberry  roots  as  slightly  more  resistant  than  the  currant. 

Preventive  and  Remedial  Treatments. — Danger  of  root  injury  may  be 
permanent  or  temporary.  If  the  past  history  of  the  locality  shows 
extensive  root  injury  the  grower  should  bear  this  in  mind  as  a  possible 
threat.  If  his  site  is  sandy  or  chronically  dry  or  wind  swept  in  winter  he 
is  threatened  continually  and  may  be  justified  in  accommodating  his 
orchard  practice  accordingly.  A  temporary  condition  of  danger  may 
occur,  such  as  a  dry  autumn,  in  orchards  ordinarily  safe.  Early  winter 
cold  snaps  are  most  to  be  feared,  because  the  roots  are  then  tender  and 
there  is  less  likely  to  be  a  snow  covering.  However,  it  may  be  February 
that  brings  disaster. 

Deep  Planting  and  Mulching. — Preventive  methods  are  more  effi- 
cacious and  generally  cheaper  than  palliative  measures.  Deeper  planting 
than  usual,  if  the  winter  water  table  is  not  too  high,  may  protect  the 
roots,  especially  in  the  first  winter.  Protective  soil  coverings,  either 
mulches  or  cover  crops,  should  be  used  in  very  dry  locations;  the  advan- 
tage of  a  snow  blanket  should  be  remembered  in  choice  of  site  or  in  select- 
ing a  cover  crop. 

The  tendency  of  deep  planted  trees  to  send  out  roots  from  the  cion  is 
well  known.     Some  varieties  do  this  more  freely  than  others.     These 


316  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

roots  when  they  come  from  cions  of  extremely  hardy  varieties  are  gen- 
erally hardier  than  the  stocks  commonly  used.  In  those  of  the  northern 
sections  where  root  killing  is  most  likely  there  is  a  tendency  to  grow  trees 
formed  by  grafting  long  cions  on  short  pieces  of  root  for  the  purpose  of 
inducing  cion  rooting,  thus  securing  increased  hardiness  in  the  roots. 
No  experimental  evidence  is  available  to  show  clearly  whether  cion  roots 
of  hardy  apple  varieties  are  hardier  than  those  of  tender  varieties,  but 
Craig^^  records  numerous  instances  when  cion  roots  proved  more  hardy 
than  the  stocks  on  which  they  were  worked.  Hansen, ^^  writing  in  South 
Dakota,  says:  "  .  .  .in  ordinary  winters  the  roots  emitted  by  the 
scions  of  hardy  varieties  are  sufficiently  hardy  but  .  .  .  they  are  not 
proof  against  such  winters  as  that  of  1898-1899." 

Use  of  Hardy  Stocks. — Top  working  on  stocks  of  known  hardiness  is 
another  method  of  combating  root  killing  in  those  sections  particularly 
subject  to  it.  Pyrus  baccata  is  said  by  Hansen  to  succeed  in  the  Trans- 
baikal  section  of  Siberia  where  the  mean  annual  temperature  is  27'°F. 
and  the  mean  temperature  of  the  coldest  month  —  18.4°F.  and  where 
the  annual  rainfall  is  11.42  inches.  He  reports  young  seedlings  of  this 
species  to  have  wintered  perfectly  despite  a  temperature  of  —  40°F.  with 
no  snow.  The  "Virginia  crab"  is  also  reported  to  be  more  hardy  than 
French  crab.  However,  these  have  more  or  less  dwarfing  effect  and  do 
not  make  an  altogether    satisfactory  union. '^^^ 

Pruning. — After  the  damage  has  occurred,  there  is  little  that  can  be 
done.  If  the  killing  is  complete  or  nearly  so  the  trees  should  be  removed. 
However,  many  times  the  root  destruction  is  incomplete;  some  of  the 
roots  that  start  straight  down  from  the  crown  on  old  trees  will  frequently 
escape.  In  many  of  these  cases  a  heavy  pruning  back,  or,  if  there  is 
also  injury  in  the  top,  a  moderate  pruning  back,  will  enable  the  tree  to 
survive  and  still  have  many  years  of  usefulness.  Very  young  trees 
that  have  suffered  only  partial  destruction  of  the  roots  can  be  restored 
in  many  instances  by  banking  the  trunks  with  earth,  inducing  the  for- 
mation of  additional  cion  roots. 

Handling  Nursery  Stock  in  Cold  Weather. — One  form  of  root  injury 
likely  to  be  encountered  in  regions  remote  from  the  territory  commonly 
subject  to  killing  of  this  type  is  that  occurring  on  nursery  trees.  Root 
growth  in  apple  trees  in  Missouri  has  been  shown  to  continue  long  after 
the  top  has  assumed  a  completely  dormant  appearance,  in  fact  until 
winter  has  well  set  in. 212.  In  a  growing  state,  it  will  be  recalled,  roots 
are  damaged  by  temperatures  only  a  few  degrees  below  freezing  and 
even  in  a  dormant  state  they  will  stand  only  comparatively  high  tem- 
peratures.^^ Chandler  states:  "In  case  of  1-year-old  roots  of  the  French 
crab,  used  as  stock  by  most  of  the  nurserymen,  about  —5  to  —  8°C.  (23  to 
15.8°F.)  is  as  low  a  temperature  as  they  can  be  depended  upon  to  with- 
stand with  no  injury."     Fall  dug  trees,  necessarily  hfted  before  the 


WINTER  INJURY  TO  THE  ROOTS  317 

ground  freezes  and  often  dug  rather  early  must  have  very  tender  roots, 
so  tender  in  fact  that  exposure  to  a  sUght  frost  after  digging  in  this  stage 
is  hkely  to  have  very  serious  consequences.  Extreme  care  in  protecting 
tree  roots  against  any  freezing  from  the  time  they  are  dug  until  they 
are  planted  is  amply  justified. 

Summary. — Root  killing  is  particularly  common  in  sections  with 
low  winter  temperatures  and  little  snowfall.  Minimum  soil  temperatures 
of  24°  to  25°F.  at  a  depth  of  6  inches  are  very  common  in  deciduous  fruit 
sections  and  soil  temperatures  of  7°F.  have  been  recorded  in  Nebraska. 
Freezing  temperatures  are  frequently  registered  to  a  depth  of  2,  and  occa- 
sionally to  a  depth  of  3  feet.  The  critical  temperature  for  the  roots 
of  most  hardy  species  during  their  dormant  season  ranges  from  about 
14°  to  5°F.  During  the  growing  season  it  is  much  higher.  Minimum 
soil  temperature  is  influenced  greatly  by  soil  covering,  being  distinctly 
higher  under  snow  or  a  mulch  formed  by  some  cover  crop  than  under 
bare  ground.  Fertilizers  may  indirectly  protect  roots  against  severe 
freezing  by  promoting  the  growth  of  weeds  or  of  cover  crops.  Frost 
penetrates  more  deeply  in  light  than  in  heavy  soils.  Roots  are  killed 
more  readily  in  dry  than  in  moist  soils.  Considerable  differences  exist 
in  the  relative  resistance  of  the  roots  of  different  species  and  varieties. 
Preventive  measures  include  moderately  deep  planting,  the  use  of  cion- 
rooted  trees  or  trees  on  hardy  stocks,  the  choice  of  locations  not  unduly 
exposed  to  the  wind,  the  use  of  cover  crops  to  hold  the  snow  and  thus 
both  directly  and  indirectly  blanket  the  soil  and  in  some  cases  artificial 
mulching.  Remedial  treatment  consists  chiefly  in  judicious  pruning. 
Care  should  be  taken  in  handling  nursery  stock  that  the  roots  are  not 
exposed  to  freezing  temperatures  in  packing,  unpacking  or  heeling  in 
and  they  should  be  protected  from  freezing  while  in  storage  or  transit. 


CHAPTER  XVIII 
WINTER  INJURY  IN  RELATION  TO  SPECIFIC  FRUITS 

The  discussion  of  winter  killing  to  this  point  has  been  general.  Any 
species  furnishing  convenient  illustrative  material  has  been  drawn  on 
and  most  of  the  types  considered  affect  each  species  more  or  less;  the 
prevailing  conception  has  been  the  tree  in  general  rather  than  any  specific 
kind.  There  are,  however,  differences  in  the  problem  of  hardiness  as 
it  relates  to  the  several  species  and  detailed  points  of  adjustment  to 
these  differences.  These  can  be  considered  more  conveniently  by  dis- 
cussing each  fruit  singly,  evaluating  for  each  the  different  types  of  injury 
to  which  it  is  liable  and  indicating,  wherever  possible,  the  best  means 
of  minimizing  the  difficulties. 

The  Apple. — The  apple  is  the  most  widely  grown  fruit  in  America 
and  is,  at  one  point  or  another,  exposed  to  practically  every  form  which 
winter  injury  can  take;  it  seems,  however,  practically  immune  to  some 
of  them.  Aside  from  sunscald  there  is  little  or  no  evidence  that  the 
apple  suffers  from  those  types  of  injury  that  are  characteristic  of  late 
winter,  i.e.,  from  warm  weather  followed  by  cold.  Though  killing  of 
fruit  buds  sometimes  occurs  it  seems  hardly  probable  that  this  is  a  kill- 
ing of  buds  which  have  broken  the  rest  period.  At  the  time  of  the 
Easter  freeze  of  1920  in  the  lower  Missouri  valley  many  varieties  had 
pushed  their  buds  so  far  along  that  they  showed  pink.  These  varieties 
of  course  suffered  more  or  less  but  their  killing  constitutes  a  case  of 
damage  to  succulent  tissues  rather  than  of  winter  injury.  Late  blossom- 
ing varieties,  though  the  buds  had  swelled  noticeably,  were  not  damaged 
by  the  drop  to  14°F.  Though  this  is  not  conclusive  evidence  it  is  sugges- 
tive. A  February  freeze  of  —  7°F.  in  Georgia  when  some  Japanese  plums 
were  in  bloom,  worked  serious  injury  to  plums  and  peaches  but  caused 
no  damage  to  the  apple. ^^'^ 

Whipple-"^  introduces  clear  evidence  of  fruit  bud  killing  in  Montana 
and  shows  that  little  readily  recognized  evidence  that  the  buds  have  been 
fruit  buds  is  left  after  they  are  killed.  If  the  injury  is  confined  to  the 
floral  parts  as  Whipple  has  shown  to  be  the  case  at  times,  the  vegetative 
parts  grow  and  the  casual  observer  concludes  that  the  tree  has  failed  to 
form  fruit  buds  and  is  going  through  an  off  year.  It  is,  therefore, 
possible  that  this  killing  may  occur  at  times  when  it  is  not  recognized. 
Nevertheless  it  is  safe  to  assume  that  fruit  bud  killing  is  comparatively 
rare  and  that  when  it  does  occur  it  is  not  necessarily  related  to  the 
breaking  of  the  rest  period. 

318 


WINTER  INJURY  IN  RELATION  TO  SPECIFIC  FRUITS 


319 


Injuries  Associated  ivith  Immaiuritij. — Difficulties  due  to  prolongation 
of  the  growing  season  are  far  more  common  in  the  apple.  Indeed,  disre- 
garding the  winter  drought  conditions  in  the  north  prairie  states,  which 
are  not  apple  growing  states  in  a  commercial  sense,  it  is,  in  one  form  or 
another,  the  prevailing  type  of  injury.  A  large  proportion  of  recorded 
cases  of  winter  injury  may  be  traced  to  immatuiity.  This  probably 
accounts  for  the  many  cases  observed  in  which  the  wood  is  killed  while 
the  buds  are  not.  The  various  forms  of  injury  associated  with  imma- 
turity have  been  discussed  and  require  no  elaboration  here. 

There  remain  for  consideration,  however,  some  interesting  differences 
between  varieties  in  hardiness.  Most  European  varieties  were  early 
found  lacking  in  this  respect  along  the  Atlantic  coast  and  the  apples 
developed  in  the  eastern  states  in  turn  proved  tender  when  transplanted 
to  the  northern  prairie  states.  From  available  data  it  is  not  yet  possible 
to  reduce  varietal  differences  from  an  indefinite  empirical  status  to  a 
basis  capable  of  quantitative  expression.  Macoun's  statement,  quoted 
above  under  Immaturity,  that  hardiness  is  merely  an  expression  of 
complete  maturity,  is  undoubtedly  true  in  a  large  measure.  The  winter 
apples  of  southern  latitudes  are  tender  at  the  north  though  there  are 
exceptions,  as  Ben  Davis  which  is  probably  hardier  than  Baldwin,  and 
the  winter  apples  of  the  north,  hardy  there,  are  summer  or  fall  apples  in 
the  south.  The  summer  apple  in  the  north,  finishing  its  active  season 
early,  has  time  to  develop  maturity  such  that  it  withstands  the  winters; 
the  winter  apple  must  grow  longer  to  complete  its  cycle  and  has  less  oppor- 
tunity to  acquire  the  condition  that  makes  it  hardy.  As  an  index  of 
comparative  maturity  Beach  and  Allen^^  report  observations  on  the  date 
of  terminal  bud  formation  in  several  varieties,  which  are  reproduced  here, 
with  some  change  of  arrangement,  as  Table  49.     Despite  some  incon- 

Table  49. — Date  of  Forming  Terminal  Buds'^ 


Variety 


Nursery 
trees 


Orchard 
trees 


Variety 


Nursery 
trees 


Orchard 
trees 


Hibernal 

Oldenburg. . . . , 

Salome 

Soulard 

Virginia 

Wealthy 

Mcintosh 

Silken  Leaf  .  .  . 

Winesap 

Anisim 

Black  Annette. 


July  25 

.July  1 

Aug.  20 

July  1 

Aug.  20 

* 

Aug.  20 

* 

Aug.  20 

* 

Aug.  20 

July  12 

Aug.  28 

* 

Sept.  1 

* 

Sept.  5 

Julv  22 

Sept.  5 

* 

Sept.  20 

* 

Ben  Davis. . . 

Gano 

Jonathan .... 

Patten 

Grimes 

Delicious 

Ingram 

Iowa  Blush. . 
Lansingburg . 

M  inkier 

Roman  Stem. 


Sept.  27 
Sept.  27 
Sept.  27 


July  1 
July  10 
July  22 
July  1 
July  15 
July  22 


'Terminals  not  formed  at  time  of  first  frost,  about  Oct.  1. 


320 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


sistencies,  as,  for  example,  the  relative  positions  of  Winesap,  Ben  Davis 
and  Delicious,  there  is  a  general  correspondence  between  the  date  of  ter- 
minal bud  formation  and  the  generally  accepted  relative  hardiness  of  the 
varieties  reported  upon. 

The  water  content  of  most  tissues  may  be  taken  as  an  index  of  matur- 
ity, diminishing  as  this  condition  is  approached;  the  same  is  true  of  other 
tissues.  This  being  true  a  study  of  the  moisture  contents  of  different 
varieties  ought  to  give  an  index  of  their  relative  maturity. 

Shutt^^°  reports  an  interesting  set  of  moisture  determinations  at  Ottawa, 
reproduced  here  as  Table  50.  These  10  varieties  were  arranged  by  Macoun  in 
groups  in  decreasing  order  of  hardiness,  as  follows:  Group  1  (hardiest),  Olden- 
burg, Yellow  Transparent,  McMahon  White;  Group  II,  Wealthy,  Scott's  Winter; 
Group  III,  Scarlet  Pippin,  Walworth  Pippin;  Group  IV  (least  hardy),  Hebble 
White,  Boy's  Delight,  Blenheim  Pippin. 

Table  50. — Percentage  of  Water  in  Apple  Twigs  Jan.  23,   igOS'^" 


Variety 


Basal  portion 


Terminal 
portion 


Whole  twig 


Yellow  Transparent 
McMahon  White.  .  . 

Oldenlnirg 

Walworth  Pippin .  .  . 

Boy's  Delight 

Wealthy 

Scarlet  Pippin 

Hebble  White 

Scott's  Winter 

Blenheim  Pippin ... 


45.55 
45.45 
45.02 
44.72 
44.74 
46.82 
47.13 
49.09 
47 .  50 
48.93 


45.10 
46.96 
47.51 
47,67 

44.75 
48.72 
49.92 
48.82 
50.36 
51.38 


45.30 
46.14 
46.15 
46.20 
46.25 
47.70 
48.58 
48.91 
48.98 
50.24 


Comparison  of  Macoun's  arrangement  with  Shutt's  figures,  considering 
in  particular  the  terminal  portions  of  the  twigs,  shows  a  correspondence 
that  at  least  suggests  a  relationship.  Shutt  comments  on  these  figures  in 
part  as  follows:  .  .  .  "it  would  seem,  therefore,  that  we  have  direct 
and  definite  proof  that  there  is  a  distinct  relationship  between  the  mois- 
ture content  of  the  twig  and  its  power  to  resist  the  action  of  frost  and 
that  those  trees  whose  new  growth  contains  the  largest  percentage  of 
.water,  as  winter  approaches,  are  in  all  probability  the  most  tender." 

Table  13  shows  the  moisture  content,  at  different  dates,  of  several 
varieties  of  apples.  Of  these  Hibernal  and  Wealthy  are  generally 
recognized  as  the  hardiest.  It  is  significant  that  these  two  varieties 
had  the  least  moisture  in  July  and  that  in  January,  after  a  week  of  cold 
weather,  including  a  minimum  of  —  15°F.,  having  lost  the  smallest 
amounts  of  moisture,  they  had  the  greatest  moisture  contents.  Winesap, 
figures  for  which  were  not  complete,  dropped  in  water  content,  between 


WINTER  INJURY  IN  RELATION  TO  SPECIFIC  FRUITS  321 

July  15  and  Dec.  26,  from  60.4  to  45.7  per  cent.,  having  on  that  date  the 
lowest  water  content.  It  is  also  the  least  hardy  of  the  varieties  under 
consideration.  The  hardier  varieties  were  found  to  lose  less  water 
through  the  bark  in  a  given  time. 

Various  workers  have  studied  the  structure  of  apple  twigs  but  no  one 
has  been  able  to  correlate  definitely  any  structural  differences  with  hardi- 
ness or  its  lack.  There  seems  some  tendency  for  hardier  varieties  to 
have  somewhat  thicker  bark  and  more  starch  in  their  tissues  but  these 
characters  are  by  no  means  constant.  Were  the  starch  content  shown  to 
be  correlated,  it  could  hardly  be  regarded  as  a  causal  agent  but  more 
likely  a  product  of  the  conditions  that  make  the  variety  hardy,  through 
making  it  mature. 

In  short,  then,  the  only  character  that  can  be  linked  definitely  with 
hardiness  in  the  apple  is  maturity.  If  one  variety  is  hardier  than  another 
because  it  matures  better,  the  cultural  practices  that  make  the  tender 
variety  mature  better  make  it  in  effect  more  hardy.  A  well  matured 
tree  of  a  tender  variety  is  undoubtedly  more  hardy  than  an  immature 
tree  of  a  hardy  variety.  This  accounts  for  many  apparent  inconsistencies 
in  field  observations. 

Control  Measures. — Efforts  have  been  made  to  influence  cold  resist- 
ance by  topworking  upon  stocks  of  great  hardiness.  In  so  far  as  root 
killing  is  prevented  this  practice  has  proved  beneficial.  It  is  also  a  wise 
practice  if  the  growing  of  varieties  notoriously  subject  to  crown  rot  or 
crotch  injury  is  to  be  undertaken.  However,  that  hardiness  of  stock 
increases  the  hardiness  of  the  cion  is  not  shown  conclusively  by  any 
evidence  available.  It  is  conceivable  that  an  early  maturing  stock  might 
influence  the  top  slightly  in  the  same  direction  but  any  influence  of  this 
character  is  comparatively  insignificant.  Macoun^^^  reports  top  grafting 
varieties  not  perfectly  hardy  on  stocks  of  very  hardy  varieties  at  Ottawa, 
Ontario;  among  the  cions  used  were  Baldwin,  Benoni,  Esopus,  Fallawater, 
King,  Newtown,  Northern  Spy,  Ontario,  Rhode  Island,  Rome  Beauty, 
Sutton,  Wagener,  Winesap  and  York  Imperial;  the  stocks  used  were 
McMahon,  Gideon,  Haas  and  Hibernal.  The  grafts  endured  several 
winters,  but  "the  test  winter  of  1903-1904  killed  practically  all  of  them," 
though  the  stocks  survived.  It  is,  however,  interesting  to  note  that 
Sorauer^^^  considered  that  grafting  of  weak  growing  varieties  upon 
vigorous  stocks  results  in  an  increased  amount  of  frost  canker,  character- 
istic of  immature  tissues. 

There  is  a  limit  to  the  effects  that  can  be  induced  by  cultivation. 
No  amount  of  cultural  manipulations  can  make  a  variety  mature  its 
fruit  and  its  wood  in  a  situation  where  it  does  not  receive  sufficient  heat 
(where  the  season  is  too  short).  It  is  not  without  significance  that  only 
one  of  the  important  winter  apples  of  the  south  can  be  grown  to  any 
advantage  in  the  north.     Whether  the  cause  be  called  failure  to  mature 

21 


322  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

or  lack  of  constitutional  hardiness,  there  is  a  northern  limit  to  the  culture 
of  every  variety  and  that  limit  is  reached  more  quickly  for  some  varieties 
than  for  others. 

Varietal  Differences. — Out  of  the  vast  and  costly  experiments  in  hardi- 
ness carried  on  by  planting  and  replanting,  the  sieve  of  selection  has  shown 
certain  varieties  to  withstand  winter  cold  in  average  conditions  better  than 
others.  Since  Baldwin  is  perhaps  the  best  known  single  variety  in  most 
sections  where  apple  hardiness  is  important  it  is  used  as  a  standard  of 
reference.  Hardier  than  Baldwin  is  a  quaUty  possessed  by  but  few  varie- 
ties of  extensive  commercial  possibilities  though  this  statement  does  not 
mean  that  Baldwin  is  particularly  hardy.  In  the  list  of  varieties  recom- 
mended by  Hedrick,  Booth  and  Taylor^*  for  the  St.  Lawrence  and 
Champlain  Valleys,  where  Baldwin  does  not  succeed,  are  Fameuse, 
Mcintosh,  Oldenburg,  Wealthy,  Blue  Pearmain,  Jewett  Red,  St. Lawrence, 
Gravenstein,  Red  Astrachan,  Yellow  Transparent,  Canada  Baldwin, 
Longfield  and  numerous  crab  apples. 

For  ''the  most  northerly  district"  of  Quebec,  Macoun^^^  recommends 
Tetofski,  Blushed  Calville,  Lowland  Raspberry,  Duchess,  Charlamoff, 
Antonovka,  Wealthy,  Hibernal,  McMahon,  Longfield,  Patten  Greening, 
Mcintosh,  Milwaukee,  Winter  Rose,  Stone,  Scott  Winter  and  Malinda. 
It  is  stated  that  the  summer  and  autumn  varieties  are  the  hardiest. 

At  the  Northwest  Experiment  Farm,  in  Minnesota,  where  winter  con- 
ditions are  probably  as  severe  as  at  any  point  where  apples  can  be 
expected  to  grow%  the  list  of  approved  varieties  is  limited,  aside  from 
certain  crab  apples,  to  four:  Hibernal,  Oldenburg,  Okabena  and  Patten 
Greening. ^^^ 

If  one  variety  were  to  be  picked  as  the  hardiest  of  all  cultivated 
varieties  of  the  apple  grown  in  America  it  would  probably  be  Hibernal. 

The  Pear. — The  pear  is  like  the  apple  in  its  reactions  to  winter  con- 
ditions. It  is  somewhat  less  hardy  than  the  apple.  Though  apples  are 
grown  at  points  where  the  mean  temperature  of  December,  January  and 
February  is  13°F.,  the  northern  limit  of  the  pear  follows  in  general  the 
mean  temperature  line  of  20°F.'^^  Nevertheless  certain  varieties  possess 
considerable  hardiness.  Though  evidence  as  to  actual  hardiness  in  the 
northern  Mississippi  valley  is  not  available  because  of  the  complications 
introduced  by  fire  blight  prevalence,  some  information  may  be  secured 
from  experience  in  certain  eastern  states  where  blight  is  not  so  serious. 

Pears  suffered  extensive  injuries  in  New  York  during  the  extremely 
severe  winter  of  1903-1904.^^  Young  trees,  though  the  bark  and  wood 
were  discolored,  made  good  recovery,  in  one  case  forming  a  layer  of  5 
millimeters  over  the  old  sap  wood  in  the  first  summer.  Trees  that  had 
been  injured  by  psylla  were  killed  outright  in  many  cases.  Dehorning 
old  trees  that  were  injured  aggravated  their  poor  condition. 

Waite'^^  reports  extensive  damage  to  pears  in  the  Hudson  River 


WINTER  INJURY  IN  RELATION  TO  SPECIFIC  FRUITS         323 

valley  during  the  same  winter.  Pointing  out  that  pear  orchards  are 
planted  customarily  in  low  rich  ground,  in  other  words,  on  sites  more 
inviting  to  winter  injury  than  those  ordinarily  chosen  for  peaches,  he 
states  that  pears  were  as  severely  injured  as  peaches  and  do  not  possess  the 
recuperative  powers  of  the  peach.  Elevation  made  great  difference  in 
the  amount  of  damage.  "The  young  pear  trees  are  rather  less  hurt  than 
the  older  trees,  as  in  the  case  of  the  peach,  but  it  should  be  noted  in  this 
connection  that  young  pear  trees  having  the  wood  blackened,  although 
they  will  push  out  their  wood  and  make  a  start,  are  very  apt  to  decline  or 
else  maintain  their  life  in  a  very  feeble  manner  as  a  result  of  the  dead 
wood  at  the  heart.  They  have  not  the  ability  to  recover  by  depositing  a 
thrifty  layer  of  sap-wood.  Pear  trees  under  3  or  4  years  of  age  which  are 
badly  frozen  and  which  show  blackened  or  discolored  wood,  even  though 
the  bark  may  look  normal  from  the  outside  and  may  appear  to  be  alive 
and  quite  fresh  when  cut  into,  should  be  cut  off  below  the  snow  hne 
and  allowed  to  sprout." 

Injury  to  pears  occurred  in  the  localized  Michigan  freeze  of  October, 
1906.^^2  Though  peaches  were  killed,  it  was  only  in  low  places  and  in 
vigorously  growing  trees  that  pears  were  seriously  injured.  Blackening 
of  the  wood  was  found.  Apples  were  very  little  injured  under  the  same 
conditions.  In  parts  of  Washington  an  early  winter  freeze  caused  split- 
ting of  trunks  on  the  south  side  and  blackening  in  the  wood  of  the  fruit  spurs 
down  to  the  limbs,  with  damage  in  some  sections  to  the  blossom  buds.^^ 
Bailey*  reports  killing  of  fruit  buds  at  Ithaca,  N.  Y.,  with  no  injury  to 
wood,  during  a  dry  cold  winter.  Injury  to  wood  occurred  elsewhere,  he 
states,  at  the  same  time,  but  evidently  he  does  not  consider  this  severe. 

The  following  varieties  have  been  reported  suitable  for  culture  in 
Vermont  and  hence  presumably  hardy :  Vermont  Beauty,  Flemish  Beauty, 
Anjou,  Winter  Nelis,  Onondaga,  Tyson,  Lawrence  and  Sheldon. ^^s  As 
"succeeding  in  many  gardens"  Angouleme,  Bartlett,  Buffum,  Seckel, 
Louise  Bonne  de  Jersey  are  mentioned.  At  Orono,  Maine,  a  little  beyond 
the  northern  limit  of  the  Baldwin  apple,  the  hardier  varieties  have  been 
found  to  be  Clapp  Favorite,  Flemish  Beauty,  Howell,  Lawrence,  Sheldon 
and  Winter  NeUs.^^'  Chandler  states  that  Anjou  is  one  of  the  hardiest 
varieties  at  Ithaca,  N.  Y.,  probably  a  little  more  so  than  Clapp  Favorite 
and  Sheldon,  certainly  less  than  Flemish  Beauty.  Bartlett  is  generally 
conceded  to  be  rather  tender. 

Flemish  Beauty  has  proved  the  hardiest  variety  of  the  better  class  of 
pears  tested  at  Ottawa,  Ont."^  Evidence  elsewhere  corroborates  this 
selection,  though  even  this  varietj^  is  by  no  means  immune  to  winter 
injury  in  regions  of  commercial  fruit  growing.^"^ 

The  Peach. — The  difference  in  the  hardiness  problem  in  peaches 
north  and  south  has  been  discussed,  maturity  being  stated  as  the  leading 
factor  in  the  north,  the  rest  period  in  the  south.     Root  killing  has  been 


324  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

shown  to  be  of  relatively  small  importance  in  the  peach,  though  it  is  by- 
no  means  unknown.  Extensive  killing  occurred  in  the  Michigan  peach  sec- 
tion in  a  freeze  on  Oct.  10,  1906,  while  the  trees  were  still  in  full  foliage. ^^^ 
At  South  Haven  the  temperature  fell  to  17°F.,  and  some  unofficial  ther- 
mometers registered  6°F.  Cambium  and  sap-wood  injuries  extending  to 
the  snow  line  were  common.  Frost  cankers  on  peach  trunks  and  crotches 
are  found  sometimes,  following  winters  of  extreme  cold  or  a  late  growing 
season. ^^  "Gum  pockets  usually  form  under  the  flattened  areas  and  the 
gum  often  oozes  out  during  periods  of  wet  weather.  The  injured  area  is 
usually  rather  indefinite  about  the  margin  and  the  formation  of  a  healthy 
roll  of  callus  is  thereby  much  retarded." 

It  has  been  shown  earlier  that  no  stated  temperature  can  be  assumed 
as  fatal.  However,  fruit  buds  are  generally  more  tender  than  wood. 
When,  therefore,  there  occur  cases  in  which  the  wood  is  killed  and  the 
buds  survive,  they  may  be  considered  good  evidence  of  lack  of  maturity. 
There  is  hardly  a  winter  without  some  killing  back  of  young  twigs  which 
may  be  interpreted  as  indicating  a  lack  of  maturity.  The  care  generally 
exercised  in  selecting  sites  for  peach  orchards  to  secure  freedom  from 
spring  frosts  fortunately  has  another  equally  desirable,  though  seldom 
recognized,  effect  in  that  it  secures  greater  maturity.  There  is  a  remark- 
able uniformity,  throughout  reports  of  various  freezes  in  northern 
states,  in  locating  the  greatest  injury  in  trees  growing  in  moist,  rich  soil 
and  receiving  late  cultivation.  Another  point  of  agreement  is  the  ascrib- 
ing of  great  injury  to  trees  low  in  vitality  from  various  causes  such  as 
San  Jose  scale,  leaf  curl,  low  fertility,  borers  and  poor  drainage.  Green 
and  Ballou^i  mention  an  orchard  in  which  the  San  Jose  scale  spray  was 
omitted  in  1902  on  three  rows  running  through  the  middle.  In  the 
severe  winter  of  1903-1904  these  three  rows  were  killed  while  the  rest 
were  uninjured.  Whether  the  greater  injury  to  weak  trees  is  actual  and 
due  to  some  specific  condition  characteristic  of  weakness  or  whether  it  is 
apparent  and  due  to  their  inferior  recuperative  powers  is  not  clear.  A 
given  degree  of  injury  would  be  more  evident,  certainly,  on  a  weak  than 
on  a  strong  tree. 

Waite,^^^  reporting  on  the  January,  1904,  freeze  in  New  York,  dis- 
tinguished three  classes  of  injury:  "  (1)  In  bearing  peaches  the  trees  most 
injured  by  freezing  show  the  bark  entirely  blackened  and  dead,  more  or 
less  separated  from  the  trunk  and  the  wood  turned  a  very  dark  brown 
color.  The  injury  extends  far  up  onto  the  limbs  although  the  bark 
usually  has  not  separated  on  the  branches.  Such  trees  are  dead  beyond 
all  question.  The  bark  on  such  trees  still  retained  its  vitality.  Some- 
times a  rise  of  10  or  15  feet  resulted  in  trees  being  less  seriously 
injured.  (2)  With  many  peach  trees  the  bark  is  lightly  separated  from 
the  wood  which  is  of  a  dark-walnut  color  next  to  the  cambium  and  brown 
throughout.     Though   still   alive  the   bark   is  somewhat  browned   and 


WINTER  rXJURY  IX  RELATION  TO  SPECIFIC  FRUITS  325 

discolored,  the  youngest  or  outer  layer  of  wood  has  been  frozen  until  it  is 
now  of  a  dark-walnut  color  and  the  wood  is  blackened  throughout. 
Many  of  these  trees  are  of  doubtful  vitality  and  will  probably  succumb. 
Others  have  enough  vitality  to  enable  them  to  pull  through.  Where 
bark  is  adhering  or  only  partially  separated  from  the  trunk  the  chances 
for  recovery  are  good.  The  tops  of  such  trees  are  usually  found  in  fair 
condition,  the  wood  brownish,  but  the  white  cambium  layer  uninjured 
though  lying  immediately  in  contact  with  brown,  dead  wood.  The 
twigs,  especially  the  1-year  wood,  sometimes  have  been  frozen  so  badly 
that  they  will  not  be  able  to  push  out  the  leaf  buds.  In  severe  cases  the 
leaf  buds  themselves  are  killed,  but,  as  a  rule,  they  are  still  alive.  Of 
course  on  all  such  trees  the  fruit  buds  are  killed.  The  most  injured  part 
is  the  trunk  just  above  the  snow  line.  ...  (3)  The  third  class,  which 
may  be  described  as  the  moderately  frozen  trees,  in  which  the  wood  above 
the  snow  line  is  blackened  but  the  bark  not  separated  from  the  wood  and 
with  the  cambium  still  apparently  alive,  although  water-soaked  and 
injured,  frequently  has  minute  brown  streaks  in  the  bark  immediately 
in  contact  with  the  cambium.  Such  trees  will  almost  invariably 
recover.  .  .  .  Nearly  every  tree  in  the  entire  Michigan  fruit  belt 
was  frozen  in  February,  1899,  so  that  the  wood  was  blackened  and  dead 
clear  to  the  bark.  A  new  layer  of  live  white  wood  formed  inward  from 
the  white  bark,  the  trees  made  a  fairly  good  growth,  having  no  fruit  crop 
to  carry,  and  bore  the  year  following  a  record  fruit  crop." 

As  in  the  apple,  the  bark  on  the  trunk  near  the  ground  seems  to 
mature  late  and  is  particularly  liable  to  injury.  After  seasons  favoring 
late  growth  mounding  of  earth  to  cover  this  region  somewhat  has  been 
found  very  profitable  insurance.  In  several  instances  in  Ohio  in  19G3- 
1904  a  few  shovelfuls  of  earth  at  the  crown  made  the  difference  between 
dead  trees  and  uninjured  trees. ^^ 

Chandler^^  records  an  interesting  case  of  mild  injury  associated  with 
immaturity.  After  a  very  rainy  August  in  1914  the  minimum  for 
the  winter,  —  9°F.,  occurred  late  in  December.  In  the  following  spring 
the  blossoms  of  several  varieties  were  at  least  three  weeks  late  in  opening. 
Examination  disclosed  injury  to  the  pith  of  the  bud,  extending  even  as  far 
as  the  pith  of  the  twig.  There  was  very  little  injiny  elsewhere.  Usually 
the  flower  parts  are  less  resistant  than  the  pith  of  the  bud  and  of  the 
twig.  The  temperature  evidently  was  not  low  enough  to  kill  matured 
buds  but  it  did  damage  the  immature  tissues.  The  trees  in  question  bore 
a  normal  crop  that  season.  Similar  cases  have  been  observed  at  other 
times.  ^* 

Treatment  of  damaged  trees  consists  of  the  ordinary  prophylactic 
measures  and  a  moderate  pruning.  Very  heavy  heading  back,  or 
dehorning,  has  proved  decidedly  injurious  when  the  bark  or  the  wood  is 
damaged;   a  fair   amount   of   pruning   is,    however,    beneficial.*^     This 


326  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

should  be  done  before  growth  starts.  There  is  a.  general  tendency  to 
overestimate  damage  and  immediately  after  a  freeze  many  orchards 
have  been  taken  out  which  would  have  recovered  in  time  had  they  been 
allowed  to  remain.  Trees  with  any  considerable  injury  to  the  trunk 
should  by  no  means  be  allowed  to  bear  fruit  in  the  season  following  the 
injury." 

Observations  by  Mer^^^  on  oaks  may  explain  the  injurious  effects 
of  very  heavy  pruning.  Investigating  old  winter  injuries  of  the  "black 
heart"  type,  he  found  considerable  starch  still  in  the  injured  wood  but 
little  in  the  wood  subsequently  laid  down,  indicating  that  the  tree  was 
unable  to  withdraw  starch  from  the  injured  tissue.  This  suggests  that 
if  the  injury  is  extensive  the  tree  will  have  difficulty  the  following  spring 
in  securing  sufficient  carbohydrates  to  sustain  growth  until  a  supply  can 
be  secured  from  the  new  leaves.  If  the  pruning  is  heavy  enough  to 
remove  all  the  buds  which  make  new  growth  most  readily  the  difficulty 
must  be  increased.  If,  however,  no  buds  are  removed  the  scanty  carbo- 
hydrate supply  is  apportioned  to  so  many  growing  points  that  none 
receives  enough  to  sustain  growth  until  it  can  become  self-supporting  and 
the  tree  dies  of  carbohydrate  starvation. 

Hardiness  in  wood  and  in  bud  are  not  always  combined  in  the  same 
variety.  Elberta,  generally  considered  hardy  in  wood,  seems  tender  in 
the  fruit  buds.  Hedrick,^^  reporting  a  questionnaire  of  New  York  and 
Michigan  peach  growers,  states  their  selections  for  wood  hardiness  as 
follows:  For  New  York  in  order  named,  Crosby,  Hill's  Chili,  Stevens' 
Rareripe,  Gold  Drop  and  Elberta;  for  Michigan,  Hill's  ChiH,  Crosby, 
Gold  Drop,  Kalamazoo  and  Barnard.  Jaques  Rareripe,  Wager,  Carman, 
Belle  of  Georgia,  Hale's  Early,  Champion  and  Greensboro  are  listed  as 
hardier  than  the  average  in  this  respect.  Early  Crawford,  Late  Craw- 
ford, Chair's  Choice,  St.  John  and  Niagara  are  rated  as  the  five  most 
tender  in  wood  of  the  varieties  commonly  grown  in  New  York.  Salway 
is  listed  as  tender  in  Michigan. 

In  fruit  buds.  New  York  growers  find  greater  hardiness  in  Crosby, 
Hill's  Chili,  Triumph,  Gold  Drop,  Stevens'  Rareripe  and  Kalamazoo; 
Michigan  growers  find  Hill's  Chili,  Gold  Drop,  Crosby,  Kalamazoo  and 
Barnard  hardiest.  Concerning  the  five  most  tender  varieties  in  bud 
there  is  entire  agreement  in  New  York  and  Michigan  as  to  the  order  of 
their  tenderness:  Early  Crawford,  Late  Crawford,  Chair's  Choice, 
Reeves'  Favorite  and  Elberta.     The  Peento  group  is  extremely  tender. 

The  Cherry. — Sweet  cherries  are  generally  known  to  be  far  more  tender 
than  the  Dukes,  Amarelles  and  Morellos.  As  outlined  by  Finch'^'*  the 
northern  range  of  cherries  is  marked  by  the  mean  winter  temperature  of 
about  16°F.  For  the  three  coldest  of  the  pomological  districts  into 
which  the  United  States  is  divided  in  the  fruit  catalog  of  the  American 
Pomological  Society  only  one  variety  of  sweet  cherry,  Black  Tartarian 


WINTER  INJURY  IN  RELATION  TO  SPECIFIC  FRUITS  327 

is  recommended  and  that  recommendation  is  confined  to  one  district. 
For  the  same  districts  13  varieties  of  Duke  and  Morello  cherries  are 
recommended. ^^^  Of  26  varieties  in  the  catalog,  13  are  recommended 
for  District  1  and  of  these,  10  evidently  are  considered  worth  growing  in 
District  2  which  includes  most  of  the  northeastern  fruit  growing  sections. 
The  three  leading  commercial  varieties,  Early  Richmond,  Montmorency 
and  English  Morello,  are  considerably  hardier  than  the  Baldwin  apple. 
However,  some  of  the  hardiest  apples  appear  to  be  hardier  than  the  hard- 
iest cherries.  Hansen*^  states  that  root  killing  is  the  one  great  difficulty 
in  cherry  growing  in  South  Dakota.  Following  the  February,  1899,  freeze, 
with  a  minimum  of  -27.5°F.,  at  Madison,  Wis.,  some  root  killing  was  rep- 
orted, but  most  varieties  brought  their  fruit  buds  through,  Large  Morello, 
Late  Morello,  Shadow  Amarelle,  Dyehouse  and  Ostheim  having  over 
90  per  cent,  live  buds.^^  Curiously  enough  many  varieties  undamaged 
in  the  1899  freeze  had  their  buds  killed  in  the  winter  of  1896-1897  with  a 
minimum  of  —  23°F.  During  the  summer  of  1896  the  trees  had  been  in 
sod  and  there  was  much  dry  weather.  Considerable  variation  in  the 
hardiness  of  the  embryo  flowers,  not  alone  between  varieties,  but  on  the 
same  tree  and  even  within  the  same  bud,  has  been  reported. ^^  Careful 
study  showed  a  strong  inclination  toward  tenderness  in  varieties  having 
the  greater  number  of  flowers  per  bud  and  a  similar  susceptibility  in 
individual  buds  within  the  variety.  The  periphery  of  the  tree  had  39.9 
per  cent,  live  buds  while  the  central  part  had  69.9  per  cent,  alive.  Goff 
did  not  regard  this  difference  as  due  alone  to  the  greater  number  of  flowers 
in  the  peripheral  buds  but  suggested  that  it  might  be  due  to  the  protection 
afforded  by  the  branches  and  to  conduction  of  heat  along  the  trunk  from 
the  soil.  Roberts, ^^^  also  working  in  Wisconsin,  reported  that  though 
winter  injury  to  cherry  buds  is  frequent  in  that  state,  it  is  rarely  severe 
enough  to  affect  seriously  the  yield  of  fruit.  Frequently  only  one  or  two 
of  the  four  or  five  blossoms  within  the  bud  are  killed.  Studies  made  in 
the  spring  of  1917  are  interesting  in  several  respects.  All  injury  had  been 
confined  to  blossom  buds.  Older  trees  showed  more  injury  than  young 
and  the  exposure  appeared  to  have  little  relation  to  the  amount  of  injury 
during  that  winter.  Trees  which  had  been  partly  defoliated  by  the  shot 
hole  fungus  the  previous  season  received  less  bud  injury  than  normal  trees. 
The  shortest  and  the  longest  spurs  were  less  injured  than  spurs  of  medium 
length  and  on  terminal  shoots  there  was  less  injury  in  the  buds  at  the 
base  and  at  the  tip  than  along  the  central  portion  of  the  shoot.  Larger 
buds  were  most  frequently  injured. 

The  injury  occurred  early  in  December  following  a  temperature  of 
-12°F.  and  could  not  have  been  due  to  development  excited  by  warm 
winter  weather.  Microscopic  study  showed  that  the  buds  most 
damaged  were  the  most  advanced  in  their  development.  Late  maturity 
could  not  have  been  the  factor  involved  as  the  trees  and  parts  of  trees 


328  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

growing  latest  were  the  least  injured.  This  finding  is  in  agreement  with 
Goff's  earlier  report  of  greater  tenderness  in  the  winter  of  1896-1897  when 
the  trees  stood  in  sod  and  the  weather  was  dry,  both  of  which  conditions 
favor  early  formation  and  rapid  development  of  fruit  buds.  It  appears, 
then,  that  cultural  practices  tending  to  promote  vigorous  growth  and 
fairly  late  maturity  would  have  some  effect  in  reducing  injury  of  this  sort, 
though  Roberts  states  that  it  could  not  be  eliminated  altogether. 

In  a  general  way,  it  may  be  said  that  the  cherry  is  not  very  liable  to 
injuries  associated  with  immaturity.  Some  varieties  of  sweet  cherries 
were  shghtly  injured  in  Michigan  in  October,  1906,  when  peach  trees  were 
killed  and  pears  considerably  injured  in  some  places. ^^^  Cherries,  how- 
ever, showed  considerable  injury  in  Washington  in  late  November, 
1896,  at  a  temperature  somewhat  below  0°F.^2 

Bessarabian,  Brusseler  Braun,  Lutovka,  English  Morello  and  Early 
Richmond  appear,  from  the  scant  data  available,  to  be  the  hardiest  of 
the  commonly  grown  varieties. 

The  Plum. — Perhaps  because  of  the  number  of  botanical  species  from 
which  the  cultivated  varieties  have  sprung,  plums  show  a  wide  range  in 
hardiness;  though  some  are  more  tender  than  the  majority  of  peaches, 
others  are  hardier  than  the  hardiest  apples.  Hedrick^^  states  that  the 
Nigra  plums  are  the  hardiest  of  our  tree  fruits  and  are  able  to  resist 
nearly  as  much  cold  as  any  cultivated  plant.  Only  a  little  less  hardy  are 
the  Americanas.  The  relative  hardiness  of  the  other  groups  is  thus 
summarized  by  Hedrick:  "Insititias  as  represented  by  Damsons  come 
next  with  varieties  of  Domestica  as  Arctic,  Lombard  and  Voronesh 
nearly  as  hardy.  The  Domesticas  are  less  hardy  than  the  apple,  ranking 
in  this  respect  with  the  pear.  Of  Domesticas  the  Reine  Claude  plums 
are  as  tender  to  cold  as  any  though  some  consider  Bradshaw  more  tender. 
.  .  .  The  Triflora  (Japanese)  plums  vary  more  in  hardiness  than  any 
other  of  the  cultivated  species.  Speaking  very  generally  they  are  less 
hardy  than  Domesticas,  the  hardiest  sorts,  Burbank  and  Abundance,  being 
somewhat  hardier  than  the  peach,  while  the  tenderest  varieties,  of  which 
Kelsey  is  probably  the  most  tender,  are  distinctly  less  hardy  than  the 
peach.  Of  the  remaining  plums,  the  Hortulana,  Munsoniana  and 
Watsoni  groups,  there  are  great  diversities  in  opinion  as  to  hardiness. 
Probably  all  the  varieties  in  these  last  groups  are  as  hardy  as  the  peach 
with  a  few  sorts  in  each  more  hardy  than  the  peach.  It  is  to  be  expected 
from  the  more  northern  range  of  the  wild  prototypes  that  the  Hortulana 
and  Watsoni  plums  are  somewhat  hardier  than  Primus  Munsoniana.'' 

Waugh^o-*  indicates  distinct  varietal  ranges,  within  the  species: 
"  The  tenderness  of  Bradshaw  seems  to  belong  more  to  the  fruit  buds  than 
to  the  wood  and  correspondents  do  not  seem  to  agree  in  their  reports; 
but  upon  the  basis  of  statistics  received,  we  may  trace  the  northern  limit 
of  the  Bradshaw   .    .    .   which  runs  from  100  to  300  miles  south  of  the 


WINTER  INJURY  IN  RELATION  TO  SPECIFIC  FRUITS  329 

line  traced  for  Lombard.  .  .  .  In  fact  a  majority  of  the  standard  varie- 
ties, such  as  Coe  Golden  Drop,  Italian  Prune,  Jefferson,  Lincoln,  Moore 
Arctic,  Pond,  Shippers'  Pride  and  Washington,  would  probably  be  found 
to  conform  fairly  well  to  the  same  limits  as  Lombard."  Of  the  Japanese 
plums,  "Abundance,  Chabot  (Chase,  Yellow  Japan),  Hale,  Red  June, 
Willard  and  Ogon  seem  to  be  about  as  hardy  as  Burbank.  Satsuma 
stands  about  midway  between  Burbank  and  Kelsey." 

In  North  Dakota,  Waldron-°^  states:  "Only  one  species  of  plum 
(Americana)  can  be  grown  with  any  success  in  the  State.  So  far  as 
tried  here  they  are  all  hardy  though  some  ripen  late  and  most  of  them 
are  vigorous  and  productive.  .  .  .  All  things  considered  they  are  the 
easiest  and  most  profitable  fruit  to  grow  in  North  Dakota.  .  .  .  For 
general  cultivation  the  following  varieties  will  be  likely  to  succeed:  De 
Soto,  Forest  Garden,  Weaver,  Cheney,  Wolf,  Rolling  Stone,  and  Wyatt. " 
In  parts  of  Minnesota  RoUing  Stone,  De  Soto,  and  Surprise  are  too  late  in 
ripening  their  fruit  to  be  satisfactory  in  cultivation,  though  they  are  not 
stated  to  lack  hardiness."  For  the  colder  parts  of  Vermont  several 
varieties  have  been  reported  to  be  as  hardy  as  the  sugar  maple :  Stoddard, 
Hawkeye,  Quaker,  Aitkin,  Surprise,  Cheney,  De  Soto,  Forest  Garden, 
Wolf,  Wyant  and  Weaver,  ^os 

In  Wisconsin  many  varieties  have  brought  their  buds  through  a  tem- 
perature of  —  38°F.  in  one  winter,  though  they  succumbed  to  — 23°  in 
another,  ^^  indicating  that  the  condition  of  the  tree  makes  a  considerable 
difference  in  the  amount  of  cold  that  can  be  endured.  In  view  of  the  work 
of  Chandler  with  peaches  and  Roberts  with  cherries  it  seems  possible  that 
the  advancement  of  the  buds  when  they  enter  the  resting  stage  may 
have  much  to  do  with  their  hardiness.  No  definite  data  are  available, 
unfortunately,  on  this  point,  but  the  superior  hardiness  of  the  Americana 
group,  which  is  late  in  maturing,  appears  to  justif.y  investigation.  It 
would  seem,  since  plum  blossoms  are  injured  more  frequently  than  the 
woody  parts,  that  maturity  might  be  delayed  safely  to  some  extent 
without  unduly  increasing  liability  to  injury  in  other  ways.'*^ 

Recent  investigations  in  Minnesota  indicate  that  some  of  the  injury  to  plum 
blossoms  is  associated  with  early  breaking  of  the  rest  period.  Treatment  to 
increase  hardiness  by  retarding  blossom  formation  and  development  would  tend 
also  to  delay  the  breaking  of  the  rest  period. 

The  Grape. — Winter  killing  is  not  so  prominent  a  factor  in  grape 
growing  as  it  is  with  some  of  the  tree  fruits.  Two  reasons  may  be  assigned 
for  this  comparative  freedom  from  injury.  First,  varieties  grown  com- 
mercially in  the  majority  of  sections  subject  to  winter  killing  are  de- 
scended, at  least  in  part,  from  the  native  species  and  therefore  profit 
from  the  adjustment  of  the  native  species  to  their  environments.  Second, 
the  difficulty  ox  seeming  satisfactory  ripening  of  the  fruit,  because  of 


330  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

the  shorter  growing  season,  tends  to  hmit  the  northward  spread  of  grape 
culture  to  points  with  winter  extremes  well  within  the  adaptation  of 
the  vine. 

Nevertheless,  the  grape  is  far  from  immune  to  winter  injury.  Varie- 
ties with  Vinifera  qualities  predominating  or  from  species  native  to 
regions  of  mild  winters  have  distinct  climatic  limitations  and  even 
the  so-called  hardy  varieties  frequently  suffer.  There  is  little  evidence 
to  connect  winter  drought  with  winter  injury  except  in  so  far  as  a  dry 
soil  freezes  deeper.  Heavy  winter  irrigation  has  proved  of  no  value 
with  Viniferas  in  New  Mexico. '^^  Under  very  severe  conditions  root 
killing  may  occur;  at  times  the  vines  are  killed  to  the  ground  and  there 
are  frequent  instances  of  killing  of  fruit  buds  because  of  imperfect  matu- 
rity. Gladwin''^  records  three  seasons  out  of  eight  at  Fredonia,  N.  Y., 
when  the  vines  did  not  reach  proper  maturity.  Sometimes  heavy  rains 
late  in  the  growing  season  bring  about  this  condition;  again  it  may 
be  due  to  the  ripening  of  a  heavy  crop.  The  light  crop  usually  following 
a  heavy  fruiting  is  commonly  ascribed  to  exhaustion  of  the  vines  but 
it  may  be  due  also,  at  least  in  part,  to  the  killing  of  a  large  number  of 
imperfectly  matured  buds.  Since  the  grape  bud  is  compound  and  mixed, 
the  primary  floral  parts  may  be  killed  and  only  the  secondary  shoot 
develop  the  following  spring.  This  tends  to  obscure  the  kilhng  and  the 
sterility  of  the  shoot  is  attributed  to  exhaustion  following  the  heavy 
crop  of  the  preceding  season.  Gladwin  shows  that  the  three  lightest 
crops  of  the  period  studied  followed  the  seasons  when  the  sugar  content 
of  the  grapes  (an  index  of  maturity)  was  lowest.  However,  since  vines 
which  have  not  borne  are  affected  also  much  of  the  immaturity  must 
come  from  other  causes.  Indeed,  Budd-^  considered  immaturity  and 
tenderness  to  result  from  the  lack  of  a  crop  and  remarked  that  the  wood 
of  Rogers'  hybrids  ripened  well  when  bearing  a  crop  but  without  a  crop 
did  not  mature.  Much  greater  injury  has  been  reported  in  low  ground, 
particularly  in  ground  with  poor  drainage. 

At  times  very  low  temperatures,  even  when  the  vines  are  mature, 
will  cause  a  discoloration  of  the  wood  without  actually  killing  the  vine. 

Anthony^  reports  recent  investigations  of  the  practicability  of 
growing  certain  Vinifera  varieties  in  the  eastern  United  States.  When 
a  moderate  amount  of  winter  protection  is  given,  by  bending  the  vines 
down  and  covering  with  a  few  inches  of  earth,  very  satisfactory  results 
are  obtained.  Indeed,  with  the  varieties  tested,  the  hmiting  factor 
seemed  to  be  the  heat  and  length  of  the  growing  season  rather  than  tender- 
ness to  winter  cold.  Anthony  states:  "A  well  matured  Vinifera  is  seldom 
killed  outright  by  the  winter  even  if  given  no  protection,  but  the  effect  of 
the  first  winter  is  usually  to  decrease  the  plant's  vitahty  to  such  an 
extent  that  it  is  unable  to  reach  proper  maturity  the  next  season  and  so 
is  usually  killed  the  second  winter. " 


WINTER  INJURY  IN  RELATION  TO  SPECIFIC  FRUITS         331 

Mounding  has  been  effective  in  protecting  Vinifera  grapes  in  New 
Mexico"  and  hardy  grapes  in  Iowa  were  satisfactorily  wintered  by  a 
sUght  mounding  about  the  trunks  and  a  slight  covering  of  the  tips  of 
the  canes  with  soil.-'  Straw  protection  has  been  less  satisfactory  on 
Viniferas  in  New  York  than  laying  the  vines  down  and  giving  a  slight 
earth  covering.  Vines  treated  in  this  last  manner  have  proved  hardy 
in  very  trying  climates. 

Severe  freezes  in  grape  growing  regions  damage  all  varieties  so  that 
a  close  estimate  of  hardiness  in  such  places  is  difhcult.  However,  as 
the  culture  extends  into  colder  regions  varietal  differences  become  more 
evident.  The  American  Pomological  Society's  catalog  highly  commends: 
for  Section  I,  Brighton,  Cottage,  Diamond,  Herbert,  Lady,  Lindley, 
Moore  Early,  Moyer,  Niagara  (?),  Victor,  Winchell  (Green  Mountain), 
Woodbury  and  Worden;  for  Section  II,  Janesville  and  Winchell;  for 
Section  XIV,  Diamond  is  the  only  variety  to  receive  even  a  qualified 
recommendation.  ^^^ 

For  Vermont,  Waugh^o^  recommends  Moore  Early,  Worden,  Moyer, 
Brighton,  Wyoming  Red  and  Green  Mountain.  The  Northwest  Minne- 
sota Experiment  Station  for  a  more  trying  situation  recommends  Beta, 
Janesville  and  Campbell  Early.  ^^^  Hansen  in  South  Dakota  expresses 
preference  for  Worden,  Concord  and  Moore  Early  in  favorable  situations 
and  for  unfavorable  locations,  Janesville.  ^^  The  difficulty  with  Concord 
in  Vermont  appears  to  arise,  not  from  its  lack  of  hardiness  but  rather 
from  the  brevity  of  the  growing  season. 

THE  SMALL  FRUITS 

Though  winter  killing  in  cane  fruits  is  common,  more  common, 
perhaps,  than  it  is  among  tree  fruits,  conditions  of  plant  and  environ- 
ment favoring  or  reducing  injury  are  far  less  understood.  This  is  due, 
in  part  to  the  large  number  of  units  involved  so  that  the  loss  of  a  few 
plants  is  hardly  noticed,  in  part  to  the  short  normal  life  of  a  cane  fruit 
plantation  so  that  even  an  extensive  loss  is  not  as  calamitous  as  that  of 
an  orchard  and  in  part  to  the  quick  recovery  of  the  plants  from  the  com- 
mon forms  of  winter  injury.  When  a  tree  trunk  is  severely  injured 
recovery  is  a  matter  of  several  years,  if  indeed  it  is  ever  complete. 
Raspberry  or  blackberry  canes,  on  the  other  hand,  may  kill  to  the  ground 
but  only  one  crop  is  lost  and  the  following  autumn  generally  finds  the 
plants  in  as  good  condition  as  ever. 

The  growing  of  small  fruits  has,  in  most  of  the  northern  sections, 
because  of  these  conditions,  developed  along  two  lines;  in  some  cases  only 
hardy  varieties  are  grown  and  no  winter  protection  is  given  and  in  others 
protection  is  given  and  desirable  varieties  grown  regardless  of  their 
hardiness.  Hence  inquiry  into  hardiness  as  it  relates  to  small  fruits 
generally  has  taken  the  form  of  variety  testing  for  this  quality;  related 


332  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

experimental  data  are  very  meager.  Field  observations  as  recorded  are 
frequently  contradictory  and  puzzling.  A  certain  variety,  for  example, 
half  hardy  in  New  York  would  be  expected  to  be  wholly  adapted  to 
Georgia;  actually  it  may  prove  fully  as  tender  in  the  south  as  in  the  north. 
The  red  raspberry  as  a  group  is  generally  conceded  in  northern  regions  to 
be  hardier  than  the  blackcap  group  yet  the  reverse  condition  obtains  over 
wide  areas. ^^  Though  loganberry  and  other  western  dewberries  are  very 
tender,  in  one  winter  at  Corvallis,  Ore.,  with  a  minimum  of  20°F.,  when 
Cuthbert  raspberries  were  killed  at  the  collar  the  loganberry  was  un- 
harmed. Furthermore,  cane  fruits  frequently  suffer  from  drought  injury 
which  is  doubtless  sometimes  confused  with  winter  injury  and  so  reported. 

Winter  injury  to  cane  fruits  may  take  one  of  several  forms.  Root  kill- 
ing occasionally  occurs,  especially  in  dry,  cold  climates  with  little  snow. 
Where  this  occurs,  covering  the  canes  is  of  no  avail  unless  the  roots 
also  are  covered.  In  other  cases  the  canes  may  kill  to  the  ground,  or 
they  may  kill  part  way  back,  or  the  laterals  may  kill.  Immature  canes 
appear  to  kill  more  easily  at  the  tips  and  close  to  the  ground  and  would 
sometimes  be  benefited  by  mounding.  The  canes  may  be  weakened  only 
and  blossom  but  fail  to  mature  the  crop.  Under  exceptional  conditions 
currant  and  gooseberry  fruit  buds  may  be  killed  while  the  stems  live. 

Immaturity  Most  Important.— It  is  a  generally  accepted  principle  in 
the  growing  of  cane  fruits  that  maturity  is  important  to  hardiness.  Imma- 
ture tips,  laterals  on  canes  pinched  back  and  suckers  that  develop  late  are 
sometimes  injured  by  comparatively  mild  freezing;  a  temperature  of  12°F. 
in  November  has  caused  extensive  damage  to  raspberry  tissues  of  this 
sort  in  Missouri.  Even  in  Virginia  caution  about  late  cultivation, 
inducing  an  immature  and  tender  growth,  appears  necessary.^  That  the 
degree  of  maturity  attained  at  the  onset  of  cold  weather  can  be  modified 
by  cultivation,  irrigation  and  fertilization  is  obvious. 

Relation  of  Summer  Pinching  to  Maturity. — The  effect  of  pinching 
on  raspberries  in  northern  sections  where  maturity  is  clearly  a  factor 
with  tree  fruits  is  well  illustrated  by  Table  51,  which  shows  the  resistance 
to  winter  killing  of  different  varieties  pinched  at  15  to  20  inches  and  of  the 
same  varieties  unpruned.  It  is  evident  that  the  lateral  growth  induced 
by  pinching  is  not  so  hardy  as  the  unbranched  canes;  presumably  this  is 
due    to    immaturity. 

A  statement  of  Michigan  experience  is  not  without  interest. ^^^ 
"Hansell,  King,  Miller  [red  raspberries]  seldom  branch  and  should  not 
be  pinched  back.  When  allowed  to  grow  naturally  the  canes  form  strong 
buds  from  which  the  fruiting  branches  will  be  developed  the  following 
season  while  if  the  ends  are  pinched  the  buds  will  develop  the  first  year 
into  slender  shoots  upon  which  the  fruit  buds  will  be  weak,  .  .  .  [with 
an]  increased  tendency  toward  winter-killing.  Hence,  for  non-branching 
varieties  pinching  back  is  not  to  be  recommended."     However,  Card*^ 


WINTER  INJURY  IN  RELATION   TO  SPECIFIC  FRUITS         333 


Table  51.— Winter  Resistance  of  Pruned  and  Unpruned  Raspberries" 
(10  =  no  injury) 

Pruned 

Unpruned 

Protected 

Unprotected 

Protected 

Unprotected 

9.0 
9.0 
2.0 
7.0 
8.0 
7.0 
8.0 
5.0 
8.0 
8.0 
7.0 
7.0 
8.0 
7.0 
7.0 
9.0 
8.0 

7.3 

4.0 
7.0 
2  0 
5.0 
7.0 
4.0 
4.0 
5.0 
4.0 
6.0 
4.0 
4.0 
6.0 
5.0 
4.0 
6.0 
6.0 

4.9 

10.0 
9.0 
4.0 
9.0 
9.0 
9.0 
8.0 
8.0 
8.0 
9.0 
9.0 
9.0 

10.0 
8.0 
9.0 
9.0 
9.0 

8.6 

5.0 

Springfield              

7.0 

Royal  Church 

Carman     

5.0 

8.0 

Thompson  Early  Prolific .  .  . 

Herstine 

Parnell                  

7.0 
6.0 
5.0 

Golden  Queen 

Reider 

5.0 
4.0 

Brandy  wine 

7.0 
6.0 

Marlboro              

5.0 

Hansen         

7.0 

Clarke  

5.0 

Cuthbert 

7.0 

Turner                              .  .  . 

6.0 

Caroline                

7.0 

6.0 

Average  pruned,       6 .  08 
Average  unpruned,  7 .  29 

reports  instances  in  which  canes  growing  fairly  late  in  the  season  have 
been  hardier  because  they  were  smaller  and  of  more  compact  growth  and 
in  reality  better  matured.  It  is  worthy  of  note,  also,  that  it  is  a  common 
practice  among  dewberry  growers  in  the  South  Atlantic  states,  where 
winter  injury  to  cane  fruits  is  by  no  means  unknown,  to  mow  all  canes 
after  the  fruit  has  been  picked;  evidently  no  serious  winter  killing  to  the 
late  growing  shoots  results. 

Varietal  Differences  from  Year  to  Year. — Phenological  notes  on 
cane  fruits  are  not  sufficiently  extensive  to  indicate  whether  there  is  any 
correlation  between  varietal  behavior  in  regard  to  maturity  and  resistance 
to  cold  weather.  Comparison  of  the  dates  of  ripening  of  fruit  with  the 
recorded  degree  of  winter  killing  fails  to  establish  any  connection;  the 
same  is  true  with  regard  to  the  date  of  blossoming.  There  is,  furthermore, 
some  inconsistency  in  varietal  behavior.  Table  52,  arranged  from  reports 
on  variety  tests  of  blackberry  in  Massachusetts,  shows  a  considerable 
fluctuation  in  the  percentage  of  canes  killed  in  successive  winters,  with  a 
considerable  difference  in  varieties.  Thus  Agawam's  record  is  30-0-0 
while  Erie's  is  20-20-80.     This  indicates  that  more  than  one  factor  must. 


334  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

be  operative  in   determining  hardiness  and  that  though  maturity  is 

frequently  very  important,  it  is  by  no  means  to  be  considered  the  sole 

factor. 

Table  52. — Percentage  of  Blackberry  Canes  Killed  in  Successive  Winters'^^ 

1890  1891  1892 

Agawam 30  0  0 

Early  King 10  12  8 

Erie 20  20  80 

Minnewaski 0  8  5 

Snyder 10  0  0 

Wachusett, 20  0  10 

Western  Triumph 30  8  3 

Wilson 20  5  40 

Injuries  from  Drought  not  Uncommon. — Any  variety  may  be  weak- 
ened from  drought  or  fungous  diseases  and  suffer  unduly  the  following 
winter.  It  is  well  known  that  large  amounts  of  moisture  in  the  soil 
induce  winter  killing  and  that  accumulation  of  ice  on  the  surface  of 
the  soil  has  the  same  effect.  The  relation  of  winter  drought  to  winter 
killing  is  perhaps  less  appreciated.  Some  unpublished  investigations 
by  Emerson  in  Nebraska  on  this  matter  are  of  great  importance, 
pointing  as  they  do  to  the  conclusion  that  "injury  to  raspberries 
in  that  locality  was  apparently  almost  wholly  a  matter  of  winter 
drying.""  Canes  coated  with  paraffin  suffered  no  appreciable  injury 
while  untreated  canes  on  the  same  stools  were  killed  to  the  ground  or  to 
the  snow  line.  Observing  that  when  the  snow  cover  was  deep  enough 
to  keep  the  soil  from  freezing  the  canes  were  not  injured,  even  in  the 
parts  that  projected  above  the  snow,  Emerson  tried  to  secure  the  same 
results  by  mulching.  Various  mulches  were  tried  and  the  ground  was 
in  many  cases  kept  from  freezing  but  the  canes  were  killed  down  to  the 
mulch.  "Temperature  readings  taken  at  various  depths  in  the  mulch 
indicated  that  for  a  period  of  some  weeks  a  portion  of  the  mulch  was 
continuously  below  the  freezing  point.  Of  course,  the  water  absorbed  by 
the  roots  from  the  unfrozen  ground  could  not  pass  through  the  frozen 
part  of  the  cane.  Other  studies  suggested,  though  I  perhaps  did  not 
have  sufficient  data  to  prove  it,  that  the  canes  are  not  frozen  for  any 
length  of  time  when  surrounded  by  snow."^^ 

Card^'^  remarks  that  though  in  Nebraska  covering  of  raspberries 
and  blackberries  is  necessary  the  same  varieties  are  commonly  grown  in 
New  York  without  protection,  despite  the  fact  that  the  winters  in 
Nebraska  are  no  colder.  He  reports  that  during  one  winter  in  Nebraska 
when  the  mercury  fell  below  zero  (Fahrenheit)  but  once,  with  —5°  as  the 
minimum,  unprotected  canes  were  killed.  Plants  in  adjoining  rows 
exactly  alike,  except  that  they  were  laid  down  and  covered,  were  entirely 
uninjured.     The  following  winter  was  much  colder  but  the  soil  was  moist 


WINTER  INJURY  IN  RELATION  TO  SPECIFIC  FRUITS         335 

from  autumn  rains  and  both  raspberries  and  blackberries  came  through 
in  good  condition  without  protection.  Growers  of  raspberries  in  Wyom- 
ing are  advised  to  stop  irrigation  about  Aug.  1  but  to  give  a  heavy  late 
fall  irrigation,  besides  covering  the  plants. ^^  There  is  general  agreement 
that  cane  fruits  suffer  more  in  seasons  and  in  sections  with  little  snow. 

It  is  possible  that  much  of  the  benefit  attendant  upon  covering  canes 
comes  from  the  reduced  drying  out  rather  than  from  actual  protection 
from  cold.  Even  a  trivial  protection  seems  sufficient,  sometimes  just 
enough  to  hold  the  canes  down.  Lying  prostrate  without  covering  they 
escape  most  of  the  drying  effect  of  the  wind;  when  covered  with  earth 
or  snow  they  will  resist  extreme  cold.  Such  protection  is  essential  in 
some  sections,  in  others  the  profit  in  the  operation  depends  on  the 
variety  grown.  Thus,  in  some  experiments  at  Ottawa  it  was  found  that 
the  increased  yield  resulting  from  protection  of  the  hardiest  varieties 
did  not  repay  the  cost  of  the  operation  though  other  less  hardy  varieties 
thus  treated  gave  16  to  22  per  cent,  greater  yields  or  enough  to  leave  a 
profit  for  the  work.*^  Incidentally,  it  was  reported  that  the  plants  thus 
protected  ripened  their  crops  5  to  8  days  ahead  of  those  not  protected. 
In  Colorado  minimum  temperatures  around  zero  ordinarily  do  not  neces- 
sitate covering  raspberry  canes ;^^  in  New  York  unprotected  raspberry 
plantations  stand  considerably  lower  temperatures  without  material 
injury. 

Group  and  Varietal  Characteristics. — The  small  fruits  as  a  class 
exhibit  a  rather  wide  range  of  hardiness.  Currants  probably  are  to  be 
regarded  as  the  hardiest  of  all  cultivated  fruits,  with  gooseberries  only 
slightly  less  so.  Next  in  order,  in  the  north  at  least,  come  the  red  rasp- 
berries descended  from  native  species — those  of  Europe  are  tender — 
followed  by  the  blackcap  raspberries  which  in  turn  are  hardier  than  the 
blackberries.  There  is  some  overlapping;  the  hardier  black  raspberries 
are  hardier  than  the  more  tender  of  the  red  raspberries  and  some  black- 
berries in  turn  are  hardier  than  certain  of  the  raspberries.  Least  hardy 
of  all  are  the  dewberries,  which  are  really  tender  though  their  trailing 
habit  makes  possible  their  culture  much  farther  north  than  their  upright 
hybrids  with  the  blackberry  can  be  grown  without  protection.  The 
dewberry  and  the  blackberry,  like  the  plum,  are  derived  from  several 
native  species  and  their  range  in  hardiness  is  correspondingly  wide.  The 
loganberry.  Phenomenal  berry  and  allied  forms  are  tender  to  tempera- 
tures below  15°F.  and  the  Himalaya  and  Evergreen  blackberries  are 
very  little,  if  any,  hardier.  On  the  one  hand,  then,  is  the  currant,  hardier 
without  protection  than  the  apple  or  the  plum;  on  the  other  is  the  dew- 
berry, rather  less  hardy  than  the  peach  though  it  is  sometimes  grown 
where  the  peach  is  not  grown,  because  it  is  more  easily  protected. 

Among  currants  the  smaller  Red  Dutch  and  Raby  Castle  types  are 
considerably  hardier  than  the  large-fruited  varieties,  the  Fay  and  Cherry 


336  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

types.  12^  Gooseberries  rarely  suffer  from  winter  killing  but  where 
comparison  has  been  possible  Houghton  seems  the  hardiest,  with  Down- 
ing and  Industry  only  slightly  less  resistant.  Turner  seems  for  a  long 
time  to  have  been  considered  generally  the  hardiest  of  the  older  red 
raspberries;  though  the  newer  Sunbeam  and  Ohta  appear  even  hardier, 
a  large  number  of  varieties,  such  as  Hansell,  Marlboro  and  Herbert, 
are  hardy  enough  for  all  but  the  most  trying  climates.  Hardier  than 
many  of  the  red  raspberries,  particularly  those  with  European  ancestry, 
are  the  hardiest  blackcaps,  including  Plum  Farmer  and  Older.  Of  the 
blackberries,  Snyder  is  generally  the  hardiest,  with  Eldorado  and  Agawam 
ranking  close  to  it.  Lucretia  is  perhaps  the  most  widely  grown  dewberry 
in  the  northern  states,  being  grown  successfully  in  Iowa  and  Minnesota 
when  covered  with  soil  through  the  winter. 

Summary. — Though  winter  injury  from  other  causes  sometimes 
occurs,  both  the  apple  and  the  pear  suffer  most  from  those  forms  asso- 
ciated with  immaturity.  Certain  cultural  practices  encourage  earlier 
maturity,  but  in  these  fruits  protection  against  winter  injury  is  most 
readily  secured  by  a  judicious  selection  of  varieties.  The  peach,  plum 
and  cherry  suffer  from  injuries  associated  with  immaturity  and  with 
an  early  breaking  of  the  rest  period,  the  latter  being  the  most  important 
with  the  peach  and  certain  plums  and  the  former  with  other  plum  groups 
and  the  cherry.  Protective  measures  lie  principally  in  controlling  season 
and  degree  of  maturity,  though  something  can  be  accomplished  by  selec- 
tion of  varieties.  Grapes  suffer  mainly  from  those  forms  of  winter 
injurj^  associated  with  immaturity.  Varieties  show  great  differences 
in  their  hardiness.  In  addition  to  the  protective  measures  adapted  to 
the  tree  fruits  protection  by  artificial  covering  of  the  canes  during  the 
winter  is  sometimes  practicable  with  this  fruit.  The  small  fruits  show 
a  wide  range  in  hardiness,  some  of  them,  as  the  currant  and  gooseberry 
being  among  the  hardiest  and  others,  as  the  western  dewberries,  being 
very  tender.  The  bramble  fruits,  in  addition  to  being  subject  to  a 
general  killing  back,  are  particularly  susceptible  to  injury  at  the  crown. 


CHAPTER  XIX 

THE  OCCURRENCE  OF  FROST 

Though  spring  and  autumn  frosts  determine  the  geographic  Hmits 
of  certain  fruits  less  frequently  than  minimum  winter  temperatures, 
they  are  nevertheless  of  no  small  importance  in  fruit  production.  There 
are  some  whole  sections  of  the  country,  as  for  instance  the  high  table 
lands  of  eastern  Oregon,  where  fruit  growing  is  very  uncertain  because 
frost  may  occur  at  almost  any  time  during  the  growing  season.  There 
are  many  other  sections  or  areas  where  spring  frosts  frequently  occur 
so  late  that  certain  fruits  such  as  the  apricot  or  the  almond  cannot  be 
successfully,  or  where  autumn  frosts  are  so  early  that  late  maturing 
fruits  such  as  the  grape  do  not  ripen  properly  and  consequently  are  not 
grown.  Furthermore,  within  regions  or  sections  that  are  suitable  for 
fruit  culture  there  are  many  sites  or  locations  which,  because  of  their 
susceptibility  to  frost,  are  unsuited  for  orchard  purposes  or  where,  if 
fruit  is  planted,  it  requires  expensive  artificial  protection  from  frost. 
Finally,  there  come  years  when  untimely  frosts  levy  a  heavy  toll  on 
the  fruit  crop  in  isolated  places  or  over  wide  areas  generally  considered 
to  be  favorably  located  for  fruit  production.  Early  autumnal  frosts 
seldom  cause  concern  so  far  as  the  season's  crop  is  concerned,  though  in 
grapes  and  some  of  the  late  maturing  or  everbearing  types  of  small 
fruits  they  may  be  responsible  for  considerable  damage.  On  the  other 
hand,  comparatively  few  and  exceptionally  fortunate  are  the  fruit  growers 
who  are  entirely  free,  year  after  year,  from  concern  about  possible  spring 
frosts.  The  cost  of  full  protection  from  spring  frosts  of  certain  pear 
orchards  in  the  Rogue  River  valley  has  amounted  sometimes  to  $40 
per  acre.  It  is  quite  likely,  however,  that  many  crop  failures  arising  from 
other  causes  are  attributed  to  frost  damage  and  it  is  certain  that  much 
can  be  done  to  lessen  this  injury  by  the  careful  selection  of  kinds  and 
varieties  of  fruit  adapted  to  the  particular  situation  or  by  selecting 
a  situation  suitable  to  the  kinds  or  varieties  of  fruit  that  it  is  desired  to 
grow.  Furthermore,  under  favorable  circumstances  much  can  be  accom- 
plished by  palliative  methods,  such  as  heating  the  orchard. 

FROST  FORMATION 

Though  discussion  of  the  nature,  occurrence  and  prediction  of  frosts 

belongs  properly  in  treatises  on  meteorology,  a  brief  outline  of  the 

more  important  facts  concerning  frost  formation,  so  far  as  they  concern 

the  fruit  grower,  seems  necessary  here  because  this  subject  is  not  studied 

22  337 


338  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

SO  widely  as  is  warranted.  It  should  be  understood,  however, 
that  cold  weather  aside  from  frosts  may  damage  fruit  crops  and  it  is 
not  always  necessary  that  the  temperatures  go  below  the  freezing  point. 
Dorsey  shows  that  cold  weather,  though  the  temperature  remains  above 
freezing,  immediately  following  the  pollination  of  certain  plum  varieties, 
results  in  such  a  slow  growth  of  the  pollen  tube  that  abscission  of  the 
style  often  takes  place  before  fertilization,  the  result  being  as  complete 
failure  to  set  fruit  as  though  frost  had  actually  occurred  during  the 
blossoming  period.  Low  temperatures  also  prevent  the  bees  from 
effecting  pollination. 

Frosts  and  Freezes  Distinguished. — Furthermore,  not  all  freezing 
temperatures  are  due  to  frosts.  English  writers  use  the  term  "frost" 
to  designate  freezing  temperature  of  any  kind  but  usage  in  the  United 
States  restricts  ''frost"  to  a  kind  of  cooling  well  recognized  and  limited 
in  its  scope.  A  "freeze,"  as  distinguished  from  a  frost,  is  due  to  the 
importation  of  cold  air  from  other  regions  and  may  be  accompanied  by 
a  high  wind;  a  frost  is  due  to  a  local  cooling  of  air  and  occurs  during 
calm  weather.  A  frost  may  take  the  form  called  a  "hoar"  frost,  with 
a  visible  deposit  of  frozen  moisture,  or  it  may  be  a  "dry"  or  "black  frost" 
with  freezing  temperatures  but  with  no  deposit.  Freezing  temperatures 
may  accompany  snow  squalls.  All  of  these  may  injure  orchard  fruits. 
Against  freezes  the  fruit  grower  is  generally  unable  to  contend  by 
palliative  methods;  against  frost  much  effort  has  been  expended  and  it 
is  upon  frost  that  much  horticultural  thought  has  been  centered. 

Relation  of  Radiation  to  Frost. — Some  knowledge  of  the  nature  of  radiation 
is  necessary  to  a  proper  understanding  of  the  nature  of  frost.  It  is  generally 
considered  by  physicists  that  all  substances  are  constantly  receiving  and  emanat- 
ing heat.  This  radiation  heat  travels  in  straight  lines  through  ether  and  through 
air,  being  absorbed  by  them  little  or  none.  Striking  a  solid  substance  it  is  in 
part  reflected  and  in  part  absorbed,  the  amounts  of  reflection  and  of  absorption 
varying  with  the  substance.  During  a  clear  day  the  heat  received  by  any  sub- 
stance through  radiation  from  the  sun  and  from  other  substances  is  in  excess  of 
the  amount  emitted  through  radiation;  during  a  clear  night  the  heat  lost  by 
radiation  exceeds  that  gained.  On  a  cloudy  day  the  sunlight  is  cut  off  to  a 
great  extent  and  the  substance  is  warmed  less  than  on  a  clear  day;  during  a 
cloudy  night  much  of  the  heat  lost  by  radiation  is  reflected  by  the  clouds  and  the 
substance  is  cooled  less  than  on  a  clear  night.  There  is  some  absorption  of 
radiant  heat  by  the  atmosphere.  Radiant  heat  from  the  earth  is  absorbed  by 
water  vapor,  carbon  dioxide  and  ozone. 

Radiation  is  proportional  to  the  exposed  surface,  and  the  amount  of  heat 
stored  and  available  for  radiation  is  to  a  large  extent  proportional  to  the  volume 
of  the  radiating  substance.  Therefore  vegetation,  which  has  a  large  surface  in 
proportion  to  its  volume,  cools  by  radiation  with  relative  rapidity. 

Though  air  freely  permits  the  passage  of  radiation  heat,  it  radiates  little 
itself  in  comparison  with  other  substances.     There  is,  it  is  true,  an  appreciable 


THE  OCCURRENCE  OF  FROST  339 

amount  of  radiation  from  the  air.  The  rapid  cooling  of  air  after  sunset  is  largely 
a  radiation  effect,  especially  if  the  air  at  higher  elevations  is  rather  free  from 
water  vapor  as  is  usually  the  case  with  a  high  barometer.  However,  in  compari- 
son with  radiation  from  the  earth's  surface  that  from  the  air  is  small.  Coming 
in  contact  with  radiating  and  therefore  cooler  substances,  air  loses  heat  to  them 
by  conduction  and  is  thereby  cooled.  If  the  air  is  in  motion,  the  cooled  air  and 
the  warmer  air  form  a  mixture  which  is  constantly  coming  in  contact  with  the 
radiating  substances  bringing  to  them  fresh  supplies  of  heat.  If,  on  the  other 
hand,  the  air  is  calm,  the  cooling  of  the  radiating  substances  and  therefore  of  the 
adjacent  air  continues  as  long  as  conditions  remain  stable,  frequently  till  the 
sun  rises. 

Temperature  Inversion. — Evidently  the  nocturnal  cooling  of  the 
air  is  largely  dependent  on  the  cooling  of  the  earth's  surface  by  radia- 
tion. The  cooling  effect  is,  therefore,  most  marked  near  the  surface, 
but  since  on  even  the  stillest  night  the  air  becomes  somewhat  mixed  its 
temperature  may  be  affected  for  from  200  to  600  feet  above  the  surface, 
the  effect  becoming  less  with  increasing  height. ^^^  During  the  day  the 
temperature  decreases  at  the  normal  adiabatic  rate  with  increasing 
distance  from  the  earth.  This  relation  is  unchanged  at  night  except  in 
so  far  as  it  is  disturbed,  as  shown  above,  by  radiation  up  to  a  height  of 
200  to  600  feet.  There  is,  then,  at  night,  first  an  increase  in  temperature 
with  distance  above  the  earth,  followed  by  the  normal  adiabatic  decrease. 
This  phenomenon  is  known  to  meteorologists  as  the  temperature  inversion. 

The  extent  of  the  temperature  inversion  is  indicated  by  Table  53,  showing  the 
averages  of  observations  made  throughout  the  year  at  varying  heights  above  a 
thermometer  placed  on  grass  and  fully  exposed  to  the  sky,  expressed  in  relation 
to  the  readings  of  this  thermometer.  The  steepness  of  the  inversion  varies  from 
night  to  night  and  it  is  more  marked  in  some  localities  than  in  others  but  it 

Table  53. — Average  Temperatures  at  Different  Heights  Compared  to  that 

IN  Grass"! 

Distance  above  Grass  Increase  (Degrees  Fahrenheit) 

1  inch  3 

6  inches  6 

1  foot  7 

12  feet  8 

50  feet  10 

150  feet  12 

necessarily  exists  whenever  frost  occurs.  This  temperature  inversion  causes 
frost  but  it  also  makes  possible  the  combatting  of  frosts  by  orchard  heating  as 
shown  later.  Humphreys^^  points  out  another  interesting  relation  of  this  in- 
version to  frost  damage:  " .  .  .  it  is  obvious  that  the  tops  of  open  and  sparsely 
foliaged  trees,  especially  if  rather  tall,  often  are  less  subject  to  frost  and  more 
easily  protected  than  are  the  lower  limbs.  On  the  other  hand,  when  the  tree  is 
low  and  its  outer  foliage  sufficiently  dense  to  produce  a  protecting  canopy  over 
the  under  and  inner  branches,  as  is  generally  the  case  with  orchard  trees,  the 


340  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

difference  between  the  free  radiation  from  the  exposed  fruit  and  the  restricted 
radiation  from  that  which  is  covered  may  usually  be  sufficient,  even  when  there 
is  a  marked  temperature  inversion,  to  subject  the  former  and  not  the  latter  to  the 
greatest  danger  from  frost  and  freeze." 

Radiation  and  Thermometer  Readings. — The  full  importance  of  radia- 
tion to  the  horticulturist  needs  emphasis.  Lack  of  recognition  of  this 
factor  has  diminished  the  value  of  much  investigational  work.  A  ther- 
mometer exposed  to  the  open  air  is  radiating  and  receiving  heat.  During 
a  clear  night  the  outgoing  exceeds  the  incoming  heat  and  the  thermometer 
registers  a  lower  temperature  than  that  of  the  air.  Inside  a  shelter  prac- 
tically all  the  outgoing  radiation  heat  is  reflected  to  the  thermometer 
which  consequently  registers  very  close  to  the  actual  air  temperature. 
During  May  in  cranberry  marshes  in  Wisconsin  there  were  found  differ- 
ences between  sheltered  and  exposed  thermometers  over  bare  soil  averaging 
2.3°F.  for  all  nights  of  record,  including  nights  not  clear.  Occasionally 
the  exposed  thermometers  recorded  as  much  as  5.7  and  6.4°  lower  than 
the  thermometers  in  shelters.*^  Inasmuch  as  these  temperatures  were 
taken  near  the  ground  it  is  possible  that  they  represented  extreme  con- 
ditions and  would  be  of  direct  importance  only  to  the  cranberry  and 
strawberry  grower.  Sheltered  and  unsheltered  thermometers  at  a 
height  of  5.5  feet  from  the  ground  at  Williamstown,  Mass.,  showed  dif- 
ferences at  the  time  of  the  minimum  temperature  averaging  1.6°  and 
a  maximum  difference  of  4°F.^^^  It  is  evident,  then,  that  the  exposed  and 
sheltered,  thermometers  do  not  check  and  that  the  differences  are  not 
constant. 

Radiation  and  Plant  Temperatures. — Plants  as  well  as  thermometers 
lose  heat  by  radiation,  Seeley^^^  working  with  strawberries  found  con- 
siderable difference  between  plant  temperatures  and  air  temperatures. 

He  reports  in  part  on  his  results  as  follows:  "The  plant  thermometer  readings 
were  usually  lower  than  the  air  temperature  in  the  early  morning,  the  minimum 
usually  being  about  3  or  4°[F].  lower  than  the  air,  the  difference  being  greater, 
of  course,  when  the  weather  was  clear  with  but  httle  wind  velocity.  The  plant 
cooled  off  more  rapidly  than  the  air  in  the  early  evening  so  that  at  7  p.  m.  it  was 
usually  3  or  4°[F.]  lower  in  temperature  than  the  surrounding  air."  At  times 
the  temperature  of  the  plant  may  fall  to  8°C.  below  that  of  the  surrounding  air 
and  plants  may  be  frozen  stiff  though  the  thermometer  indicates  one  or  two 
degrees  above  zero  (C.),i"  and  there  are  records  showing  that  occasionally  plants 
are  cooled  by  radiation  to  a  temperature  12  to  15°F.  below  that  of  the  surrounding 
air."2  Tomato  vines  under  apple  trees  sometimes  escape  frost  when  those 
exposed  to  radiation  are  killed  and  the  temperature  on  a  lawn  under  a  tree  may 
be  5°  higher  than  in  the  open.i^'^ 

Observations,  predictions  and  conclusions,  then,  must  be  made  with 
three  standards  in  mind:  the  air  temperature,  the  exposed  thermometer 
temperature  and  the  plant  temperature.     Though  the  exposed  ther- 


THE  OCCURRENCE  OF  FROST  341 

mometer  doubtless  registers  closer  to  the  plant  temperature  than  the 
sheltered  thermometer,  it  must  be  remembered  that  predictions 
are  based  on  and  apply  to  sheltered  thermometer  readings.  The  dif- 
ferences between  the  three  temperatures  maj^  not  be  great  but  they  are  at 
times  great  enough  to  vitiate  conclusions  drawn  from  observations  and 
they  may  conceivably  become  at  times  great  enough  to  have  material 
effects. 

Dewpoint  and  Its  Relation  to  Frost. — Air  is  commonly  known  to 
contain  more  or  less  water  vapor.  Other  things  equal,  the  higher  its 
temperature  the  more  vapor  it  can  contain  and  conversely  the  lower  its 
temperature  the  less  moisture  it  can  hold.  If,  therefore,  any  sample  of  air 
be  cooled  enough  it  will  reach  the  point  where  it  can  no  longer  hold  as 
vapor  all  the  moisture  it  contains  and  some  of  it  is  deposited.  Obviously 
the  drier  the  air  at  a  given  temperature  the  farther  must  its  temperature 
fall  before  the  moisture  is  condensed.  The  dewpoint,  or  temperature 
at  which  condensation  occurs,  varies,  then,  with  the  absolute  amount  of 
moisture  present  in  the  air. 

As  radiation  proceeds  from  soil,  vegetation  and  other  substances 
it  has  been  shown  that  the  temperature  of  the  air  in  the  immediate 
neighborhood  of  these  substances  falls.  In  a  calm  this  cooling  frequently 
proceeds  to  the  point  at  which  moisture  is  condensed;  if  this  point  is  above 
the  freezing  point  dew  is  formed;  if  below,  frost  is  formed  directly.  It 
should  be  observed  that  frost  is  but  an  index  of  a  low  temperature  and  is 
not  of  itself  injurious.  It  should  be  observed  further  that  radiating  sub- 
stances, particularly  in  a  dry  atmosphere,  may  cool  the  air  several 
degrees  below  the  freezing  point  without  any  deposit  of  frost.  This  is 
the  black  or  dry  frost.  It  is  possible,  too,  for  cooling  to  be  extremely 
localized  so  that  frost  forms  when  the  free  air  temperature  is  several 
degrees  above  freezing;  frosts  have  occurred  with  a  free  air  temperature  of 
40°F. 

The  condensation  of  moisture  from  the  air  sets  free  a  certain  amount 
of  heat  and  retards  the  further  fall  in  temperature.  To  that  extent  dew 
or  even  frost  formation  is  beneficial  as  compared  with  low  temperature 
without  moisture  condensation.  It  was  formerly  assumed  that  the 
liberation  of  heat  from  condensation  would  check  any  further  tempera- 
ture fall  and  that  because  of  this  the  dewpoint  as  determined  the  previous 
evening  would  forecast  the  minimum  temperature  of  the  night.  Later 
investigations  have  shown  this  view  to  be  unwarranted. 

Relation  of  Clouds  and  Wind  to  Frost  Occurrence. — Evidently  con- 
ditions favoring  loss  of  heat  by  radiation  and  a  calm  condition  of  the  air 
combine  to  produce  dew  or  frost.  Clouds  reflect  the  heat  lost  by  radiation 
and  even  radiate  some  of  their  own  heat  so  that  the  passage  of  a  cloud  may 
for  a  short  time  raise  the  temperature  a  degree  or  two.  Therefore  cloudy 
nights,  though  still,  are  not  very  likely  to  be  frosty.     A  fair  breeze  does 


342 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


not  prevent  radiation  but  it  mixes  the  air  and  prevents  excessive  cooling 
of  any  small  portion  of  it;  therefore,  windy  nights  are  not  likely  to  be 
frosty.  It  is  the  nights  which  combine  good  radiation  conditions  with 
still  air  that  the  fruit  grower  should  watch  when  his  trees  are  in  bloom. 

INFLUENCE    OF  LOCATION  ON  DANGER  FROM  FROST 

It  has  been  shown  that  in  the  northern  hemisphere  the  blossoming  of 
fruit  trees  begins  early  in  the  south  and,  subject  of  course  to  minor  dif- 
ferences, moves  northward  at  a  rate  of  4  or  5  days  for  each  degree  of  lati- 
tude, though  somewhat  more  rapidly  to  the  west  of  a  given  point  than  to 
the  east.  If  the  date  of  the  last  killing  frost  in  the  spring  moved  north- 
ward at  the  same  rate,  the  calculation  of  the  chances  of  a  given  fruit's 
escaping  frost  at  any  location  would  be  a  simple  matter.     Unfortunately 


Fig.  32. — The  blossoming  season  of  Wildgoose  plum  for  1898.      (After  Waugh'^^*) 


conditions  are  much  more  complicated.  Dates  of  blossoming  and  of 
last  frosts  fluctuate  from  year  to  year.  There  are  local  variations 
particularly  in  the  occurrence  and  severity  of  frosts;  these  are  considered 
later.  The  present  phase  of  the  discussion  is  intended  to  point  out  that 
certain  regions  are  more  subject,  perhaps,  to  late  frosts  at  critical  times 
for  the  fruit  grower  than  other  localities. 

The  Blossoming  Season  and  Latitude. — Figure  32  shows  the  dates  of 
blossoming  for  the  Wildgoose  plum  at  various  points  in  the  United  States 
for  1898,  a  season  that  was,  on  the  whole,  rather  earlier  than  the  average. ^"^ 
Unfortunately  not  enough  data  are  available  for  the  construction  of  a 
map  showing  average  blossoming  seasons  for  any  particular  variety  of 
fruit  and  minor  fluctuations  due  to  varying  weather  in  different  sections 


THE  OCCURRENCE  OF  FROST 


343 


might  change  in  another  season  the  hnes  shown  in  the  figure.  However, 
the  figure  shows  in  a  general  way  tlie  northward  progress  of  the  blossom- 
ing season. 

Unpublished  figures  compiled  by  Phillips  give  average  data  for  several 
kinds  and  varieties  of  fruits  and  show  that  the  blossoming  season  moves 
northward  more  rapidly  in  the  Mississippi  valley  than  along  the  Atlantic 
seaboard  (c/.  Table  54).  Philhps  finds  the  rate  for  each  degree  of  lati- 
tude to  be:  along  the  Atlantic  coast,  5.7  days;  in  the  Mississippi  valley, 
4.8  days  and  for  the  Pacific  region,  3.4  days.  Somewhat  similar  relative 
progress  has  been  found  for  certain  phases  of  insect  life.^^  These  differ- 
ences between  sections  assume  importance  in  connection  with  the  dates 
of  the  last  killing  frosts. 


Table  54. — Avekage  Date  of  P'ull  Bloom  for  Several  Fruits  at  Different 

Latitudes 

{After  Phillips^'-^) 


Latitude 

Pacific 

Mississippi 

Atlantic 

section 

valley 

section 

35° 

Mar.  11 

Mar.  16 

Mar.  19 

36° 

Mar.  14 

Mar.  16 

Mar.  24 

38° 

Mar.  19 

Mar.  30 

Apr.    10 

40° 

Mar.  18 

Apr.    11 

Apr.    19 

41° 

Mar.  22 

Apr.    19 

Apr.  26 

42° 
)aralIol,s 

Mar.  27 

Apr.   27 

May     5 

Average  all  ] 

Mar.  19 

Apr.     4 

Apr.    11 

Avei^age  Date  of  Last  Spring  Frost  and  Latitude. — The  average  dates 
of  the  last  killing  spring  frosts  are  shown  in  Fig.  33.  Though  there  is 
a  general  northward  recession,  local  conditions  evidently  complicate 
this  process  in  the  extreme  so  that  latitude  alone  is  not  a  safe  guide  in 
determining  the  date  of  the  last  frost.  The  date  lines  of  last  frosts  are 
obviously  not  parallel.  As  an  example,  the  last-frost  date  line  for 
June  1  is  worth  consideration.  Barely  dipping  below  the  forty-fifth 
parallel  in  New  England  it  leaves  the  United  States  to  reappear  in 
Minnesota  where  it  remains  well  above  the  forty-fifth  parallel  until  it 
leaves  the  states  at  the  Canadian  boundary.  Entering  the  United 
States  again  in  Montana  it  moves  southward  to  New  Mexico,  almost 
to  the  thirty-fifth  parallel,  embracing  a  wide  range  of  territory  until  it 
leaves  Idaho,  reappearing  again  in  Washington. 

Average  Dates  and  Frost  Danger. — An  average  date,  if  the  data  on 
which  it  is  based  be  suflficient  to  give  it  validity,  means  that  approximately 
50  per  cent,  of  the  occurrences  are  prior  to  this  date  and  50  per  cent. 


344 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


follow  it.  If  the  average  date  of  blossoming  and  the  average  date  of 
the  last  frost  for  a  given  locality  coincide  there  are  possible  four  combi- 
nations of  events:  (1)  blossoming  before  the  average  and  frost  before 
the  average,  a  condition  which  may  or  may  not  be  disastrous  to  fruit 
at  that  point;  (2)  blossoming  before  the  average  and  frost  later  than 
the  average,  very  likely  to  be  a  disastrous  combination;  (3)  blossoming 
after  the  average  date  and  frost  before  the  average  date,  a  safe  condition, 
and  (4)  blossoming  later  than  the  average  and  frost  after  the  average, 
unsafe.  In  cases  1  and  4  the  last  frost  may  or  may  not  precede  the 
blossoming,  with  chances  balancing.     Cases  2  and  3  balance  each  other. 


Fig.  33. — Average  dates  of  last  killing  frost  in  spring.      (After  ReecP^^) 


It  appears,  therefore,  that  locations  where  the  average  blossoming  date 
and  average  last  frost  date  coincide  have  an  even  chance  of  escaping 
frost,  a  margin  of  safety  that  is  rather  small  for  growing  of  the  fruit 
in  question. 

Determining  Frost  Risks  in  Different  Sections  a7id Localities. — Averages, 
of  course,  do  not  indicate  the  range  of  the  figures  that  they  represent. 
The  range  of  last  frost  dates  may  be  considerable  at  one  point  and  limited 
at  another,  with  the  averages  identical.  Table  55  shows  variations  in 
the  last  frost  dates  on  record  for  several  stations  with  identical  average 
date  for  this  event.  Such  averages  have  only  a  limited  significance  for 
the  fruit  grower,  unless  the  fruit  he  grows  generally  blossoms  consider- 
ably later  than  the  average  date  of  the  last  frost. 

The  last  column  in  Table  55  records  standard  deviations  from  the 
average  date  of  the  last  frost,  Apr.  15  in  each  case.  This  standard 
deviation  means,  taking  Roseburg  for  example,  that  over  a  considerable 


THE  OCCURRENCE  OF  FROST  345 

Table  55. — Spring  Frost  Data  for  Selected  Stations^^" 


Station 

Average 
date 

Last  in 
9  to  10  years 

Last  in 
1895  to  1914 

Standard 
deviation 

Keokuk,  Iowa 

Cumberland   Md              .  .  . 

Apr.  15 
Apr.  15 
Apr.  15 
Apr.  15 

Apr.  30 
May    2 
Apr.  28 
Apr.  15 
May  10 

May    4 
May  12 
May    2 
May    1 
May  10 

11.7 
13.0 

New  Bedford,  Mass 

10.0 
12.4 

Roseburg,  Ore 

Apr.  15 

19.7 

period,  in  approximately  half  the  years  the  last  frost  will  occur  between 
20  days  before  Apr.  15  and  20  days  after,  or  between  Mar.  27  and  May 
5;  in  approximately  one-fourth  of  these  years  it  will  occur  before  Mar.  27 
and  in  approximately  one-fourth  of  the  years  it  will  occur  after  May  5. 
The  record  shows  that  the  latest  date  of  last  frost  for  this  station  is 
May  10.  Figure  34  shows  the  rather  considerable  range  of  standard 
deviations  in  dates  of  last  frosts  at  various  points  in  the  United  States. 


Fig.  34. — Standard  de%'iations  of  dates  of  last   killing  frosts  in  spring.      {After  Reed^^^) 

Of  greater  immediate  value  to  the  fruit  grower  is  Fig.  35,  showing 
dates  "  when  the  chance  of  killing  frost  falls  to  1  in  10.  "^^^  If  the  average 
date  of  blossoming  at  a  given  point  is  identical  with  the  date  of  the  1:10 
chance  for  that  point  the  probability  of  damage  is  slight,  being  in  fact 
3^  X  Ko  =  Ho,  or  one  chance  in  20.  This  may  happen  very  frequently 
in  cane  fruits  and  grapes,  though  in  most  cases  the  average  date  for 
orchard  fruits  would  precede  that  of  the  1:10  chance.  Comparison  of 
such  average  blossoming  dates  as  are  available  and  of  real  validity  shows 


346 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


that  very  few  orchard  fruits  have  less  than  one  chance  in  10  of  encoun- 
tering frost. 

The  data  here  presented  arc  introduced  as  suggestive  rather  than 
for  their  absohite  value.  As  pointed  out  elsewhere,  a  frost  recorded  as 
"killing,"  though  damaging  to  tender  vegetation,  may  do  little  or  no 
damage  to  fruit  blossoms;  similar  data  based  on  the  last  occurrence  of 
30°  or  29°F.  would  be  of  more  direct  value  to  the  fruit  grower.  Neverthe- 
less the  general  liability  of  certain  regions  to  frosts  damaging  to  fruits 
holds  true,  whatever  criterion  be  adopted,  and  though  it  would  be  hazard- 
ous to  apply  the  present  data  unreservedly  to  any  one  point  they  serve 


Fig.  35. — Computed  dates  when  the  chance  of  killing  frost  falls  to  1  in  10.      After  these 
dates  killing  frost  will  occur  only   10  years  in  a  century.      {After  Reed^^^) 

adequately  for  comparison  between  different  points.  Arranged  on  a 
slightly  different  basis  and  in  conjunction  with  accurate  blossoming 
charts,  which  are  not  available,  they  would  have  even  greater  value. 
At  present  only  generalizations  are  possible.  The  tendency  of  blossoming 
to  advance  more  rapidly  in  the  central  than  in  the  Atlantic  states  and  the 
irregularity  in  the  recession  of  last  frosts,  with  a  general  tendency  toward 
faster  recession  on  the  Atlantic  seaboard,  makes  a  given  fruit  more 
liable  to  frost  damage  in  the  Mississippi  valley  region  than  on  the 
Atlantic  coast,  if  local  variations  do  not  intervene. 


INFLUENCE  OF  SITE  ON  MINIMUM  TEMPERATURES 

The  air  in  the  neighborhood  of  radiating  surfaces  has  been  shown  to  be 
cooled  by  conduction  and  the  air  temperature  on  a  still  night  to  increase 
with  distance  from  the  surface.     As  the  air  in  contact  with  radiating 


THE  OCCURRENCE  OF  FROST  347 

surfaces  cools  it  becomes  more  dense  and  tends  to  sink.  It  is  then 
replaced  by  air  somewhat  warmer,  probably  for  the  most  part  flowing  in 
from  the  same  level,  which  air  in  turn  cools  and  sinks.  If  the  supply  of 
relatively  warm  air  be  extensive  enough  and  warm  enough,  the  radiating 
surfaces  may  be  kept  from  reaching  the  freezing  point.  This  frequently 
happens  on  hillsides  where  the  coolest  air  is  continuously  being  pushed 
downward  by  air  nearly  as  cool  and  warmer  air  is  flowing  in  from  the  side. 
So  much  cool  air  may  accumulate,  however,  that  it  fills  a  depression  com- 
pletely and  raises  the  level  of  warm  air.  The  warm  air  may  be  raised 
so  high  above  a  given  object  that,  as  radiation  proceeds,  the  replacing 
air  has  little  heat  to  give  up.  It  therefore  fails  to  warm  the  surface 
sufficiently  to  prevent  freezing. ^^2  Little  replacement  can  be  expected 
by  warm  au  from  above  since  it  is  lighter. 

However,  other  things  being  equal,  the  wider  a  valley  the  greater 
its  area  in  proportion  to  its  circumference;  consequently  the  reservoir 
of  free  warmer  air  at  any  level  is  greater  in  proportion  to  the  radiating 
shorehne  at  that  level.  The  higher  levels,  in  a  given  valley,  therefore, 
in  addition  to  having  better  "drainage  facilities"  for  removal  of  cold 
air  have  larger  reservoirs  of  warm  air  on  which  they  can  draw.  For 
the  same  reasons  a  slight  elevation  above  a  wide  valley  may  be  con- 
siderably freer  from  frost  than  a  higher  elevation  above  a  more  restricted 
valley. 

The  term  "air  drainage,"  used  to  signify  the  resemblance  of  the 
flow  of  cold  air  to  the  flow  of  water,  is  more  or  less  unscientific  and 
inexact. ^^^  Nevertheless  it  is  a  convenient  term;  it  suffices  for  practical 
purposes  and  doubtless  will  continue  in  use.  In  many  cases  there  is 
an  actual  flow  of  air,  closely  comparable  to  the  flow  of  water.  This 
flow  of  air  is  frequently  the  salvation  of  orchards  in  narrow  valleys 
which  otherwise  would  fill  quickly  with  cold  air. 

In  the  discussion  of  Sites  the  statement  is  made  that  air  drainage 
insuring  as  much  freedom  from  spring  frosts  as  possible  is  one  of  the 
most  important  considerations  in  picking  the  site  for  an  orchard.  It 
should  be  stated  here  conversely  that  the  best  method  of  insuring  against 
frost  and  against  the  continual  tax  of  frost-fighting  is  the  proper  selec- 
tion of  a  site.  There  are  certain  sections  where  to  secure  proper  soil 
or  plentiful  moisture  it  becomes  necessary  for  the  prospective  fruit 
grower  to  locate  on  low  sites  that  are  subject  to  frost.  He  should  recog- 
nize clearly  that  he  is  exchanging  relative  immunity  from  frost  for  other 
advantages;  the  exchange  may  be  profitable  if  the  frosts  are  not  too 
numerous  and  too  severe.  Over  a  large  part  of  the  country,  however, 
a  considerable  latitude  in  choice  is  available  and  intelligent  discrimi- 
nation in  the  choice  of  site  may  very  easily  make  the  difference  between 
considerable  profit  and  heavy  loss.  The  grower  who  is  forced  to  protect 
his  orchard  may  make  a  profit  in  spite  of  his  heavy  overhead  expense 


348 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


and  annual  tax;  the  grower  whose  location  is  such  that  he  is  comparatively 
immune  from  spring  frosts  is  more  likely  to  be  commercially  successful. 
Sometimes  the  line  that  divides  desirable  and  undesirable  locations  is  very 
finely  drawn.  Table  56  shows  minimum  temperatures  during  the  blossoming 
season  at  two  locations  not  far  apart  and  with  only  25  feet  difference  in  elevation. 
The  dissimilarities  in  average  minima  are  at  once  obvious. 

Table  56. — Minimum  Temperatures  at  State  College,  New  Mexico 

(After  Garcia''^) 

(Station  A  25  feet  higher  than  Station  B) 


March 

1 

April 

Day 

1912 

1913 

1912 

1913 

A             B 

A 

B 

A 

B 

A 

B 

1 

32.0 

24.5 

45.0 

42.0 

2 

38.0 

26.0 

40.0 

35.0 

3 

38.0 

33.0 

40.0 

36.5 

4 

49.0 

46.5 

34.0 

31.5 

5 

44.0 

45.0 

35.0 

31.5 

6 

39.0 

34,0 

51.0 

40.0 

7 

39.0 

36.0 

38.0 

36.0 

8 

40.0 

37.5 

36.0 

33.5 

9 

37,0 

34.5 

33.0 

30.5 

10 

52.0 

45.0 

38.0 

36.5 

11 

39.0 

34.0 

36.0 

35.5 

12 

41.0 

40.0 

29.0 

25.5 

13 

36.0 

33.0 

30.0 

27.0 

14 

32.0 

29.0 

31.0 

28.0 

15 

39.0 

34.0 

39.0 

35.0 

16 

1 

8.0 

13.0 

40.0 

35.5 

38.0 

35.0 

17 

2 

0.0 

16.5 

38.0 

32.5 

44.0 

40.0 

18 

2 

5.0 

20.5 

39.0 

33.0 

49.0 

44.0 

19 

4 

1.0 

35.0 

40.0 

34.0 

39,0 

35.0 

20 

4 

2.0 

38.5 

49.0 

40.0 

59.0 

45.0 

21 

3 

0.0 

27.0 

40.0 

35.0 

46.0 

44.0 

22 

3 

6.0 

31.0 

31.0 

29.0 

53.0 

43.5 

23 

3 

2.0 

26.5 

38.0 

33.0 

43.0 

42.0 

24     3 

0.0   25 

.0   1 

9.0 

17.0 

51.0 

45.0 

31.0 

27,0 

25     3 

6.0   33 

.0   2 

1.0 

19.0 

43.0 

39.0 

32.0 

29.0 

26     4 

5.0   39 

.0   3 

1.0 

26.5 

34.0 

28.5 

36.0 

33.0 

27     3 

5.0   32 

.5   3 

5.0 

31.5 

49.0 

40.0 

39.0 

35.0 

28     3 

5.0   29 

.0 

44.0 

39.0 

40.0 

36.0 

29     3 

4.0   29 

.0 

40.0 

35.5 

44.0 

40.0 

30     3 

3.0   26 

.5 

48.0 

39.0 

44.0 

40.0 

31     4 

1.0   30 

.0 

Average. .   3 

6.1   30 

.5   2 

9.1 

25.2 

40.6 

35.7 

39.7 

35.7 

THE  OCCURRENCE  OF  FROST  349 

More  important,  however,  is  the  consideration  that  Station  B  during  the 
time  covered  by  these  data  registered  temperatures  below  freezing  28  times  as 
compared  with  13  for  Station  A;  Station  B  registered  temperatures  28°F.  or 
less  14  times  while  this  point  was  reached  at  Station  A,  only  five  times.  Ana- 
lyzing the  figures  in  another  way:  in  the  spring  of  1912  Station  B  had  a  minimum 
of  practically  28°F.  as  late  as  Apr.  26  though  .Station  A  did  not  reach  this  figure 
during  the  season.  In  1913  the  last  minimum  of  28°F.  or  less  for  Station  A 
occurred  on  Mar.  26  and  for  Station  B  the  date  was  Apr.  14. 

Similar  variations  were  found  in  Nevada  between  two  points  190  feet  apart 
and  differing  in  elevation  by  13.5  feet.*^  The  average  April  and  May  minimum 
for  the  higher  station  was  42.7°F.;  for  the  lower  jt  was  39.5.°  On  selected  single 
nights  paired  observations  were  29-22,  34-31,  32-24,  39-31,  37-30.  The  diver- 
sity in  the  amount  of  fruit  grown  in  2  years  on  sites  such  as  these,  other 
things  being  equal,  must  necessarily  be  great  and  the  difference  in  expense  of 
orchard  heating  in  the  two  cases  would  be  well  worth  considering. 

In  some  cases  this  effect  is  said  to  be  somewhat  neutralized  by  the 
increased  earliness  of  higher  elevations.  As  a  rule  vegetation  is  later  at 
high  altitudes,  but  this  condition  is  reversed  frequently  between  points 
differing  in  altitude  only  a  few  hundred  feet.  An  interval  of  2  weeks 
between  the  first  blossoming  dates  has  been  reported  at  points  in  Utah 
2  miles  apart  and  with  200  feet  difference  in  elevation. ^  It  is  not,  how- 
ever, clear  that  this  was  due  wholly  to  the  elevation  since  slopes  and 
condition  of  soil  and  of  trees  were  not  stated  and  the  variations  reported 
are  certainly  much  more  marked  than  is  ordinarily  the  case,  making  1 
day's  difference  for  each  14  feet  in  elevation.  Were  the  air  constantly 
still,  during  the  whole  season  up  to  blossoming,  the  moderately  high 
elevations  might  indeed  accumulate  enough  excess  of  heat  to  make  con- 
siderable difference  but  in  nature  this  condition  obtains  only  during  a 
very  small  portion  of  the  time  and  such  differences  as  do  occur  generally 
may  be  attributed  to  other  effects. 

The  steepness  of  slope  necessary  to  effective  freedom  from  frost  varies 
with  the  local  topography.  Young^i^  states:  "From  observations  in 
the  Pomona  Valley,  California,  it  appears  that  there  is  little  if  any  advan- 
tage to  be  gained  by  locating  on  orchard  in  the  upper  portion  of  a  long 
uniform  slope  of  150  feet  or  less  to  the  mile.  However,  in  even  slight 
depressions  of  whatever  shape  or  direction  on  this  slope  the  frost  hazard 
is  likely  to  be  considerably  greater." 

MINOR  FACTORS  AFFECTING  TEMPERATURE 
Of  interest  chiefly  to  growers  of  strawberries  and  cranberries  are 
certain  differences  in  narrowly  restricted  limits,  differences  usually  small 
but  frequently  important.  Included  among  these  are  those  due  to 
elevation,  to  the  character  of  the  soil  covering  and  to  the  state  of  the  soil. 
Minor  Differences  in  Elevation. — Observations  on  three  sets  of  ther- 
mometers at  several  points  in  Williamstown,   Mass.,   with    the  upper 


350 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


thermometers  exposed  at  a  height  of  5.5  feet,  the  lower  at  0.5  feet,  show 
differences  tabulated  in  Table  57,  from  which  it  appears  that  a  strawberry 
plant  may  be  exposed  to  considerably  lower  temperatures  on  a  frosty 
night  than  the  trees  above  it  or  than  the  thermometer  in  the  ordinary 
shelter.  Milham  points  out  that  the  differences  are  greatest  at  the 
time  of  the  minimum  temperature  and  at  the  coldest  station,  in  other 
words  when  conditions  for  frost  are  most  favorable.  Strawberry  growers 
should  bear  this  in  mind  in  interpreting  for  their  own  use  forecasts  issued 
by  the  Weather  Bureau. 

Table  57. — Temperature  Differences  with  Height"'' 
(Degrees  Fahrenheit) 


Station  8 
(8  p.m.) 


station  7   Station  1  (St-,f°"J,  Station  7 


Average  difference . 
Largest  difference. 


0.5 
2.0 


1.5 
4.0 


2.1 

5.0 


0.5 
2.0 


2.0 
4.0 


2.9 
5.0 


On  the  other  hand  Cox^^  found  temperatures  at  5  inches  above  the 
soil  lower  than  those  at  the  surface,  particularly  on  nights  with  good 
radiation  conditions. 


"The  average  depression  of  temperature,"  he  writes,  "at  the  5-inch  height 
below  that  at  the  surface  for  the  season  of  1907  (May  to  October  inclusive)  was 
1°[F.].  The  average  depression  on  clear  cool  nights  probably  reached  4°.  There 
were  several  instances  of  differences  exceeding  6°."  Cox  evidently  was  not 
entirely  satisfied  with  the  possible  explanations  he  advanced  for  this  difference 
though  they  doubtless  explain  it  in  part.  He  states,  "In  a  marsh  grasses  and 
uprights  from  the  vines  interfere  slightly  with  radiation  from  the  thermometers 
placed  on  the  surface  and  it  is  probable  that  a  thermometer  or  leaf  exposed  at  an 
elevation  above  the  surface  loses  its  heat  more  rapidly  by  radiation  than  if  it 
rested  upon  the  surface  because  the  upper  one  is  not  shielded  in  any  way  and 
while  the  radiation  is  going  on  from  the  lower  one,  at  the  same  time  heat  is  being 
conducted  to  it  from  the  ground  beneath.  A  thermometer  resting  upon  the 
surface  of  the  bog  becomes  a  part  of  the  soil  or  vegetation  upon  which  it  rests, 
as  it  were,  and  is  benefited  by  the  free  conduction  of  heat  to  it  from  the  ground, 
while  the  conduction  to  and  through  the  air  is  very  slight  in  comparison ;  because 
of  these  differences  in  radiation  and  conduction,  the  surface  thermometer  usually 
registers  a  higher  temperature  than  the  instrument  a  few  inches  above.  For 
the  same  reason,  the  temperature  of  the  vegetation  at  the  surface  and  5  inches 
above  would  vary  as  these  temperatures  have  varied,  especially  when  the  surface 
vegetation  is  shielded  above.  It  is  a  matter  of  common  knowledge  that  in  the 
bogs  the  cranberries  growing  at  the  tops  of  the  uprights  a  few  inches  above  the 
ground  are  often  damaged  by  frost  while  those  lying  on  or  near  the  ground  escape 
injury." 

Cox  reports  also  two  series  of  observations  on  temperatures  at  various 
heights  up  to  36  inches  above  the  surface.     On  the  bog  the  5-inch  height  had 


THE  OCCURRENCE  OF  FROST 


351 


the  lowest  average  minimum  temperature,  the  surface  averaging  1.7°  higher  than 
the  5-inch  level  and  1.4°  lower  than  the  36-inch  level.  In  a  garden  on  upland 
the  differences  were  less.  Cox  summarizes  his  observations  on  this  point  as 
follows:  "The  temperature  at  2.5  inches  averaged  lowest,  44.5°[F.],  instead  of  at 
5  inches,  as  on  the  bog,  but  the  difference  was  very  slight  between  these  two 
elevations  —  0.1°.  The  surface  thermometer  averaged  highest,  45.5°  but  there 
was  only  1°  difference  on  an  average  between  the  two  extremes  while  the  average 
surface  reading  was  0.6°  higher  than  at  36  inches.  The  average  for  the  entire 
season  fairly  represents  the  conditions  prevailing  each  month,  the  highest  in 
each  case  occurring  at  the  surface  and  the  lowest  at  2.5  inches."  Table  58, 
compiled  from  Cox's  report,  shows  minima  for  nights  selected  because  of  the 
low  temperatures  and  indicates  no  substantial  variation  from  his  averages.^® 


Table  58. 


-Minimum  Temperatures  in  Open  Over  Sandy  Loam 
(Degrees  Fahrenheit) 


Date 

Sur- 

2.5 

5 

7.5 

10 

12 

15 

36 

(1907) 

face 

inches 

inches 

inches 

inches 

inches 

inches 

inches 

May  20 

24.9 

23.7 

23.8 

24.0 

24.8 

24.9 

25.0 

25.9 

May  21 

24.9 

22.9 

23.0 

23.1 

23.1 

23.1 

23.0 

23.8 

June     6 

34.7 

31.4 

31.5 

31.7 

31.7 

31.7 

31.2 

31.4 

Sept.  22 

28.0 

27.8 

27.8 

28.1 

28.3 

28.0 

28.2 

28.6 

Sept.  30 

25 . 0 

24.6 

24.7 

25.0 

25.2 

25.1 

25.2 

25.4 

It  is  evident  that  these  differences  are  not  constant.  Some  light  is 
thrown  on  the  effect  of  radiation  by  data  compiled  from  Greenwich 
observations  showing  that  a  thermometer  on  grass  fully  exposed  to  the 
sk}^  registered  lower  than  a  thermometer  suspended  4  feet  from  the 
ground  :'^^ 

Degrees 
fahrenheit 

On  cloudless  nights 9.3 

Half  cloudy 7.3 

Principally  cloudy 6.8 

Entirely  cloudy 3.4 

Influence  of  Soil. — Reference  is  made  again  to  Cox's  work  for  data 
concerning  the  minimum  temperatures  over  two  different  soils.  Table 
59  shows  minima  for  selected  nights  with  the  average  for  the  month. 
The  difference,  striking  at  the  surface,  becomes  very  slight  at  3  feet.  The 
differences  up  to  5  inches  are,  however,  of  no  little  significance  to  the 
strawberry  grower.  They  are  to  be  regarded  as  due  to  character  of  the 
soils,  since  other  conditions  were  uniform.  Incidentally  it  may  be  stated 
that  Cox  considers  it  possible  for  identical  atmospheric  conditions  to 
cause  a  light  frost  in  the  spring  and  not  in  the  fall  because  of  the  difference 
in  soil  temperatures  at  the  two  seasons.  To  the  extent  that  a  high  day 
temperature  indicates  considerable  heat  furnished  the  soil,  it  diminishes 

23 


352 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Table 

59. — Minimum 

Temperatures  in  Open  over  Two  Soils''^ 

(September,  1906) 

Day  of  month 

Over  peat 

Over  sand 

Differences  between  peat 
and  sand 

Surface 

5 
inches 

36 
inches 

Surface 

5 
inches 

36 
inches 

Surface 

5 
inches 

36 

inches 

5 

38.4 

33.1 

34.8 

45.0 

35.9 

35.9 

-6.6 

-2.8 

-1.1 

14 

35.6 

33.0 

34.7 

43.9 

35.0 

35.1 

-8.3 

-2.0 

-0.4 

24 

35.7 

32.5 

33.4 

41.0 

34.0 

33.5 

-5.3 

-1.5 

-0.  1 

27 

33.9 

31.0 

30.4 

40.3 

30.8 

30.3 

-6.4 

+  0.2 

+  0.1 

28 

39.8 

31.9 

35.7 

43.0 

35.7 

36.1 

-3.2 

-3.8 

-0.4 

30 

34.0 

28.8 

31.4 

39.6 

31.0 

33.0 

-5.6 

-2.2 

-1.6 

Monthly  mean.. 

50.6 

47.0 

48.7 

53.6 

48.6 

49.0 

-3.0 

-1.6 

-0.3 

the  probability  of  frost  the  following  morning.  Furthermore  Cox  states, 
"It  is  practically  impossible  for  frost  to  occur  in  the  bogs  on  the  first  cool 
night  following  a  warm  spell,  but  it  is  likely,  if  conditions  are  favorable, 
on  the  second  night  after  the  soil  has  become  cold." 

The  difference  in  temperature  over  the  two  soils  is  due  probably  to 
their  difference  in  radiating  and  conducting  powers.  Peat  absorbs  and 
radiates  heat  readily  but  of  course  the  heat  lost  by  radiation  warms  the 
air  exceedingly  little;  peat  is  a  poor  conductor  and  cannot  warm  the  air 
greatly  by  conduction.  The  sand,  though  not  as  good  an  absorber  of 
heat  is  a  better  conductor  and  warms  the  air  above  it  at  night. 

Influence  of  Soil  Covering, — A  thick  mat  of  vegetation  covering  the 
soil  prevents  much  heating  during  sunshine.  At  night,  though  it  pre- 
vents conduction  of  heat  from  the  soil,  it  radiates  heat  and  thus  tends  to 
lower  the  air  temperature  further.  It  is  not  strange  therefore  that  lower 
temperatures  are  found  over  vegetation  than  over  bare  ground.     Table 

Table  60. — Temperatures  Over  Sod  and  Over  Bare  Ground 

(After  Seeley^'"') 

(Degrees  Fahrenheit) 


p.m. 

a.m. 

Loss 

Surface,  bare  piround                                            .  .  . 

45.0 
43.0 
46.2 
43.0 

27.3 
23.9 
30.1 
23.9 

,7  7 

Surface,  sod                                                   

19.1 

Half  inch  below  surface,  bare  ground 

16.1 

11.7 

60,  giving  the  means  of  observations  on  18  morning  at  Peoria,  III.,  shows 
the  increase  in  difference  of  surface  temperatures  between  sod  and  bare 
ground  from  afternoon  to  morning.     The  sod  surface  is  2°  cooler  in  the 


THE  OCCURRENCE  OF  FROST 


353 


afternoon  and  3.4°  cooler  in  the  morning.     Below  the  surface,  however, 
the  sod  loses  less. 

In  minimum  temperatures  5  inches  above  the  surface  on  cranberry- 
bogs  considerable  difference,  according  to  the  density  of  the  vegetation, 
is  reported  by  Cox,'*^  from  observations  made  in  September,  1906.  Table 
61,  which  records  his  observations  for  the  coldest  nights,  shows  the  magni- 
tude of  these  variations  attributable  to  the  difference  in  the  amount  of 
vegetation  and  the  effect  it  has  on  soil  temperature.  Similar  inequalities 
may  be  expected  in  very  weedy  and  dense  strawberry  beds.  More  frost 
damage  has  been  observed  in  weed-infested  German  vineyards  than  in 
those  kept  clean. '^^ 

Table  61. — Minimum  Temperatures  with  Thick  and  with  Thin  Vegetation 

(After  Cox''') 
(Degrees  Fahrenheit) 


Day  of  month 

Thinly   vined 

Thickly  vined 

Difference 

5 

33.1 

28.3 

-4.8 

14 

33.0 

28.8 

-4.2 

24 

32.5 

28.9 

-3.6 

27 

31.0 

24.4 

-6.6 

28 

31.9 

28.0 

-3.9 

30 

28.8 

23.0 

-5.8 

Monthly  mean 

47.0 

43.6 

-3.4 

The  effect  of  mulching,  a  common  practice  in  strawberry  growing, 
should  be  mentioned  at  this  point.  As  a  winter  protection  the  value 
of  a  mulch  is  indubitable.  In  early  spring  a  mulch  tends  to  retard 
blossoming,  an  effect  which  may  or  may  not  be  desirable.  Once  the 
plants  are  in  blossom,  however,  a  mulch  may  invite  frost  damage. 

Lazenby'O'  reported  observations  to  this  effect:  "To  compare  temperatures 
over  mulched  and  unmulched  ground  I  took  16  observations  with  a  self-registering 
minimum  thermometer  daily  between  May  17  and  June  1  of  last  year.  The 
average  minimum  over  straw  was  43.2°;  over  bare  ground  46.4.°  The  greatest 
difference  was  7°.  This  year  the  average  minimum  over  straw  was  32.3°;  over 
bare  ground  34°  with  a  maximum  difference  of  3.5°." 

This  effect  is  due  probably  to  the  exclusion  of  sunshine  from  the 
soil  during  the  day  and  to  increased  radiation  at  night.  If  the  mulch 
is  used  to  cover  the  plants  during  frost,  its  effect  is,  of  course,  totally 
different. 

Influence  of  Soil  Moisture. — Observations  on  surface  temperatures 
in  wet  and  in  dry  sanded  bogs  at  Berlin,  Wis.,  in  1906,  indicated  a 
consistent  and  at  times  considerable,  difference.     Table  62,  compiled 


354 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Table  62. — Surface  Minimum  Temperatures  on  Dry  and  on  Wet  Sanded  Bogs 
{Adapted  from  Cox*^) 
(Degrees  Fahrenheit) 


Date 


ry  sand 

Wet  sand 

Difference 

43.9 

37.7 

-6.2 

41.0 

37.4 

-3.6 

40.3 

33.1 

-7.2 

43.0 

38.0 

-5.0 

39.6 

32.3 

-7.3 

35.8 

27.3 

-8.5 

53.6 

51.2 

-2.4 

Sept.  14 

Sept.  24 

Sept.  27 

Sept.  28 

Sept.  30 

Oct.      1 

September  mean 


by  the  selection  of  the  coldest  nights,  shows  that  at  the  very  time  when 
these  differences  are  most  important  they  are  greatest.  It  might  be 
argued  that  the  wet  sand  was  coldest  because  it  had  given  up  more 
heat;  however  it  is  stated  that  on  Oct.  1  cranberries  in  this  bog  were 
frozen,  except  in  the  dry  sanded  section.  The  lower  minimum  on  the 
wet  sand  is  attributed  to  the  heat  lost  in  evaporation  at  the  surface. 
It  should  be  remarked  that  irrigation  with  relatively  warm  water 
at  the  time  of  frost  apparently  has  proved  of  considerable  value  occa- 
sionally but  irrigation  that  merely  wets  the  soil  and  keeps  it  cold  is 
probably  injurious.  An  experimental  investigation  in  Wisconsin  showed 
very  little  difference  in  temperature  over  irrigated  and  over  unirrigated 
blocks. 

King,io2  commenting  on  the  results,  stated:  "Not  only  did  frost  form  after 
the  water  was  brought  to  the  areas  but  some  of  the  rape  leaves  became  stiff 
with  streams  of  water  flowing  both  sides  of  the  row.  It  is  true,  however,  that  a 
very  perceptible  difference  could  be  noted  in  the  degree  of  stiffness  which  foliage 
took  on  above  and  close  to  the  water,  and  that  which  was  more  distant.  For 
close  to  the  water  the  leaves  did  not  become  so  rigid  as  to  break  in  the  hand  while 
at  a  distance  from  the  water  they  did. 

"It  is  quite  possible  that  were  broad  areas  irrigated  at  such  times  the  pro- 
tection would  be  more  marked,  but  it  does  not  look  very  hopeful  for  the  protec- 
tion against  night  frosts  by  this  method,  especially  where  the  temperature  falls 
3  or  4°  below  freezing." 

It  seems  evident  from  the  data  above  that  evaporation  does  not 
interfere  with  radiation  sufficiently  to  offset  its  cooling  effect  and  that 
unless  the  water  actually  imparts  heat  it  is  deleterious.  A  thoroughly 
saturated  soil  is,  however,  likely  to  retard  frost  formation. 

Cox"^  states:  "The  explanation  is  found  in  the  high  specific  heat  of  water. 
A  certain  quantity  of  heat  lost  during  the  night  time  from  relatively  dry  ground 
and  its  vegetable  cover  cools  the  exposed  portions  of  these  poor  heat-conducting 


THE  OCCURRENCE  OF  FROST 


355 


objects  to  a  very  low  temperature.  An  equal  loss  of  heat  from  the  same  sub- 
stances when  they  are  loaded  with  moisture  results  in  only  a  small  lowering  of  the 
temperature  not  only  because  the  water  must  now  be  cooled  in  addition  to  the 
ground  and  vegetation  but,  as  we  know,  water  requires  the  removal  of  consider- 
able heat  to  cool  it  sUghtly.  The  radiation  losses  from  the  saturated  surfaces 
may  also  be  less  than  from  the  dry  surfaces." 

Evidently  looseness  in  application  of  terms  "wet"  and  "dry"  has 
led  to  some  apparently  conflicting  results.  Petit^*^  records  observations 
that  at  first  seem  contradictory  to  those  of  Cox,  since  they  indicate 
higher  temperatures  over  the  wetter  soil  (c/.  Tables,  63  and  64).     Petit 

Table  63. — Temperatures  in  Moist  and  Dry  Soils 

{After  Petit'^'>) 
(Degrees  Centigrade) 


Date  and  time 


Saturated  soil 


Apr.  23,  4.00  p.m 
Apr.  23,  7.15  p.m 
Apr.  24,  5.20  p.m 


21.6 
16.1 
6.5 


states  that  the  chief  cooling  influence  in  wet  soil,  evaporation,  is  inactive 
at  night,  that  the  moist  soil  conducts  heat  more  rapidly  than  the  dry 
and  therefore  can  receive  more  heat  from  below;  he  evidently  considers 
that  these  factors  offset  the  greater  radiation  he  ascribes  to  wet  soil  and 
the  lower  heat  storage  during  the  day.  Curiously  enough  he  finds 
that  dew  forms  earlier  and  is  more  abundant  on  the  moist  soil.  It  is 
possible,  however,  that  Cox  and  Petit  worked  with  soils  of  different 
texture  and  moisture  content  and  that  their  results  are  not  necessarily 
conflicting. 

Table  64. — Surface  Temperatures  Over  Wet  and  Over  Dry  Soils 

(After  Petit^'^) 
(Degrees  Centigrade) 


Date 


Time 

Not  watered 

4.30  p.m. 

18.2 

6.00  p.m. 

14.0 

10.00  p.m. 

6.9 

5.00  a.m. 

2.3 

5.15  p.m. 

10.6 

9.25  p.m. 

5.6 

5.55  a.m. 

4.0 

Watered 


Sept.  23 
Sept.  23 
Sept.  23 
Sept.  24 
Sept.  28 
Sept.  28 
Sept.  29 


15.6 
12.4 
7.3 
3.2 
10.6 
6.9 
5.2 


Efifect  of  Cultivation. — In  a  series  of-  observations  on  the  minimum 
temperatures  over  cultivated  and  uncultivated  soils  at  Peoria,  111.,  it 


356 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


was  found  that  cultivation  apparently  increased  the  temperature  about 
2°.^^^  Cox  states:  "It  is  as  important  to  cultivate  as  it  is  to  practice 
drainage,"  but  adds  that  "it  is  impossible  to  determine  absolutely  the 
advantage  in  exact  degrees  gained  by  cultivation,  draining  or  sanding. " 
It  is  evident  that  his  statement  refers  to  any  attempt  to  make  the 
observed  differences  fit  all  cases. 

Cultivation  is  said  by  Petit  to  increase  the  loss  from  the  surface  of 
the  soil  b}^  radiation,  diminishing  heat  conduction  from  below;  tamping 
the  soil  is  stated  to  lessen  this  danger.  It  should  be  observed  that  the 
temperatures  recorded  are  those  of  the  surface  and  not  of  the  air  above. 

Table  65. — Temperatures  at  Surface  of  Cultivated  and  Packed  Soils 

{After  PetiP^^) 

(Degrees  Centigrade) 


Date  and  time 

Packed 

Stirred 

Lumps 

July  15,  1898—4  30  p.m 

16.8 

37.9 
17.8 
14.2 

37.4 

July  15,  1898— 8. 15  p.m 

15.8 

Aug.    4,  1898 — 8.00  p.m 

12.6 

Increased  surface  of  the  loosened  soil  would  tend  to  increase  the  loss 
of  heat  by  conduction  and  might  easily  raise  the  temperature  of  the  air 
immediately  above  it,  though  the  surface  itself  be  cooled. 

Significance — Particularly  in  Small  Fruit  Culture. — A  saving  of 
2°  or  3°  may  or  may  not  be  an  important  matter  according  to  circum- 
stances and  consequently  any  one  of  the  factors  affecting  temperature 
may  in  itself  be  important.  However,  it  is  frequently  the  case  that 
several  of  them  are  operative  at  once  and  their  combined  effect  is  likely 
to  be  considerable,  particularly  on  nights  when  these  differences  are 
most  important. 

Cox  expresses  this  aptly:  "While  there  is  an  average  difference  of  3.4°  .  .  . 
between  the  minimum  thermometers  in  the  thinly  vined  and  the  heavily  vined 
sections,  a  difference  of  2.4°  .  .  .  between  the  minimum  thermometers  on 
peat  and  sanded  bogs,  both  thinly  vined,  and  a  difference  of  2.2°  between  the 
surface  and  5  inches,  it  is  obvious  why  an  average  difference  of  10°  .  .  .  can 
exist  between  a  minimum  thermometer  exposed  at  the  most  favorable  location 
as  far  as  drainage  and  sanding  and  cultivating  are  concerned  and  another  in  a 
most  unfavorable  location,  an  unsanded  peat  section  with  a  very  dense  growth 
of  vegetation,  and  poor  drainage.  [The  greatest  difference  observed  by  Cox 
was  17.1°F.]  It  is  not  strange  therefore  that  in  a  bog  where  there  is  a  variation 
in  the  conditions  of  sanding,  draining,  and  cultivation,  the  range  in  minimum 
temperatures  is  considerable,  and  that  a  portion  of  a  bog  is  seriously  injured  by 
frost  while  another  portion  completely  escapes. "*« 

These  inequalities  are  extremely  localized;  probably  none  of  them  is 


THE  OCCURRENCE  OF  FROST  357 

effective  at  the  height  of  trees  and  they  are  of  little  importance  to  the 
orchardist.  They  are,  however,  of  extreme  importance  to  the  grower  of 
small  fruits.  His  is  the  most  difficult  problem  in  heating  his  fruit  planta- 
tion but,  on  the  other  hand,  he  can  do  more  than  any  other  fruit  grower  to 
prevent  frost.  Generally  he  has  the  same  freedom  as  the  orchardist  in 
the  selection  of  site;  in  addition  he  can  take  advantage  of  minor  localized 
variations.  In  aiming  to  profit  by  them  he  is  following  cultural  prac- 
tices that  are  beneficial  to  his  fruit  plants  in  other  ways. 

Summary. — Spring  frost  is  important  in  setting  geographic  limits  to 
the  commercial  culture  of  fruits  of  some  kinds  and  in  determining  the 
regularity  of  crops,  yields  and  profits  in  practically  all  deciduous  fruit 
growing  sections.  Frost  formation  depends  to  a  considerable  extent  on 
the  radiation  of  heat  by  exposed  surfaces  during  the  night.  Because  of 
radiation  on  still  clear  nights,  temperatures  close  to  the  earth  are  lower 
than  those  at  somewhat  greater  elevations,  giving  rise  to  the  condition 
known  as  temperature  inversion.  On  account  of  radiation  the  real  tem- 
peratures of  plants  may  be  several  degrees  lower  than  those  registered  by 
sheltered  thermometers.  When  the  dewpoint  is  very  low,  freezing  will 
occur  without  frost  formation.  Clouds  and  wind  both  protect  against 
frost,  the  former  by  reducing  the  total  effect  of  radiation,  the  latter  by 
mixing  warm  air  with  that  which  has  been  cooled.  In  a  general  way 
both  the  blossoming  dates  of  fruits  and  the  average  dates  of  the  last 
killing  frosts  range  later  with  each  increase  in  latitude,  though  the  prog- 
ress of  the  two  is  not  always  parallel.  Study  of  Weather  Bureau  records 
showing  average  last  dates  of  killing  frosts,  together  with  the  standard 
deviations  therefrom,  will  make  possible  an  accurate  determination  of 
frost  danger  beyond  any  particular  date  for  any  given  locality,  though  not 
for  any  site.  Air  drainage  secured  by  suitable  elevation  is  of  considerable 
importance  in  determining  danger  from  frost  in  particular  sites.  Minor 
differences  in  temperature  within  narrow  limits  in  space  are  occasioned  by 
minor  differences  in  elevation,  amount  of  soil  moisture,  character  of  the 
soil  covering,  type  of  soil  and  system  of  cultivation.  These  are  seldom 
important  in  influencing  frost  injury  to  tree  fruits;  however,  they  may  be 
of  considerable  importance  in  small  fruit  culture. 


CHAPTER  XX 

PROTECTION  AGAINST  FROST 

The  fruit  grower  should  have,  not  only  knowledge  of  the  conditions 
under  which  frost  occurs,  but  information  as  to  the  exact  danger  points  for 
his  various  fruits  and  as  to  the  value  of  different  protective  measures  that 
may  be  at  his  disposal. 

CRITICAL  TEMPERATURES 

If  heating  is  to  be  done  it  should  be  delayed  until  the  temperature  is 
near  the  critical  point  to  save  expense  and  exhaustion  of  the  fuel  in  the 
heaters  before  morning.  If  it  is  known  that  the  blossoms  of  one  variety 
or  of  one  species  are  more  tender  than  others  protective  effort  may  be 
concentrated  more  or  less  on  the  tender  plants.  At  times  it  has  been 
assumed  arbitrarily  that  a  certain  temperature  is  fatal  and  that  because 
certain  orchards  had  been  exposed  to  that  temperature  they  would  bear 
no  crop.  Accordingly  the  calyx  spray  was  omitted,  to  save  labor  and 
expense,  only  to  have  it  appear  later  that  a  fair  crop  had  survived  the  freeze 
but  had  become  thoroughly  infested  by  codling  moth,  scab  and  other 
pests.  If,  then,  there  is  a  certain  temperature  that  is  universally  fatal 
to  the  blossoms  of  all  fruits  or  of  one  kind  of  fruit  it  should  be  known. 

A  compilation  of  temperatures  stated  as  dangerous  to  blossoms  of 
various  fruits  is  reproduced  here  as  Table  66. 

The  considerable  difference  in  the  damaging  points  as  stated  by  these 
various  writers  is  significant  and  it  seems  probable  that  the  range  of 
killing  temperatures  is  as  great  if  not  greater  than  indicated  by  the  table; 
West  and  Edlefsen  state  that  there  is  sometimes  a  spread  of  5°''.  The 
variations  in  temperatures  between  sheltered  thermometers,  exposed 
thermometers  and  plant  tissues  make  field  observations  of  only  limited 
value.  Variations  in  radiation  conditions  make  the  correction  of  ther- 
mometer readings  to  plant  temperatures  uncertain.  Furthermore, 
different  blossoms  must  be  exposed  to  radiation  in  varying  degrees  because 
of  diversity  in  their  positions  in  the  cluster  and  on  the  branch. 

Assuming,  however,  that  temperatures  can  be  measured  accurately, 
as  doubtless  has  been  done  in  closely  controlled  work  such  as  that  of 
Chandler  and  of  West  and  Edlefsen,  the  final  result  is  still  a  complex 
involving  several  factors  whose  separate  measurement  is  difficult. 
Several  blossoms,  alike  in  development,  will  show  differences  in  their 

35S 


PROTECTION  AGAINST  FROST 


359 


Table  66. — A  List  of  "Danger  Points"  as  Given  by  Different  Authors 

Degrees  Fahrenheit 

{After  West  and  Edlefsen,-'^''  with  additions) 


Closed  but 

Fruits 

showing 
color 

In  blossom 

Setting 

Authority 

Apples 

27 

29 

30 

1 

27 

29 

30 

2 

27 

29 

30 

3 

25 

28 

28 

4 

25 

28 

28 

5 

25 

28 

29 

6 

Peaches 

20 

25 

28 

1 

29 

30 

30 

3 

29 

30 

30 

2 

22 

28 

28 

4 

25 

27 

27 

5 

25 

26 

28 

6 

Cherries 

22 

28 

29 

1 

29 

30 

30 

2 

22 

28 

28 

4 

25 

28 

30 

6 

Pears 

27 

29 

29 

1 

29 

29 

29 

2 

28 

29 

29 

3 

25 

28 

28 

4 

25 

28 

30 

6 

Plums 

30 

31 

31 

1 

30 

30 

31 

2 

30 

31 

31 

3 

22 

28 

28 

4 

25 

28 

30 

6 

Apricots 

30 

31 

32 

2 

30 

31 

32 

3 

22 

28 

28 

4 

25 

27 

30 

6 

Prunes 

30 

31 

31 

2 

30 

31 

31 

3 

28 

29 

30 

6 

Almonds 

20 

27 

30 

7 

Grapes 

30 

31 

31 

7 

Authorities:  (1)  Wilson,  W.  M.= 
(4)  Paddock  and  Whipple. "^  (5) 
(7)  Young,  Floyd  D.^is 


"     (2)  O'Gara,  P.  J.i 
W.    H.    Chandler.  =8 


1     (3)  W.  H.  Hainmon.  ^1 
(6)    Garcia  and  Rigney.^^ 


resistance  to  the  same  freezing;  different  trees  of  the  same  variety  will 
set  materially  different  crops;  finally,  varieties  are  unequally  susceptible. 
It  is  impossible  at  present  to  state  to  what  extent  fruit  blossoms  are 


360  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

or  can  be  supercooled,  at  what  temperature  ice  formation  occurs  or  at 
what  temperature  damage  results.  General  sudden  freezing  following 
supercooling  is  considered  in  itself  injurious. ^^^  To  what  extent  this 
applies  to  fruit  blossoms  cannot  be  stated  at  present.  Indeed  it  is  possible 
that  under  natural  conditions  supercooling  as  ordinarily  understood 
does  not  occur  in  fruit  blossoms.  The  influence  of  capillarity  on  freezing 
in  these  tissues  cannot  be  stated  now.  It  is,  however,  safe  to  conclude 
that  critical  temperatures  as  determined  by  laboratory  methods  would 
be  somewhat  lower  than  would  appear  from  field  observations  with  ordi- 
nary thermometer  exposures,  because  of  the  differences  between  air 
temperatures  and  plant  temperatures  under  the  radiation  conditions 
accompanying  most  frosts.  For  the  same  reason  precise  determination 
of  killing  points  would  not  be  of  direct  application  in  the  orchard.  Paren- 
thetically it  may  be  remarked  that  the  insufficient  recognition  of  radia- 
tion effects  on  plant  tissues  in  horticultural  investigation  may  account 
for  many  of  the  conflicting  results  secured. 

However,  studies  in  artificial  freezing  are  interesting,  though  the 
high  degree  of  humidity  that  accompanies  them  is  not  invariably  present 
in  nature.  This  high  humidity  may  serve  conceivably  to  inoculate 
the  plants  with  freezing  nuclei  and  cause  freezing  at  higher  temperature 
than  would  be  required  in  a  drier  atmosphere.  Despite  limitations, 
however,  the  tests  by  artificial  freezing  possess  considerable  significance. 
West  and  Edlefsen  have  reported  some  rather  extended  investigations 
of  this  sort. 

In  part,  they  summarize  their  results  as  follows:  "Ben  Davis  apple  buds  in 
full  bloom  have  experienced  temperatures  of  25,  26,  and  27°F.  without  injury, 
but  28°  usually  killed  about  one-fifth.  Twenty-nine  degrees  or  above  are  safe 
temperatures.  Twenty-five  degrees  kills  about  one-half  and  22°  about  nine- 
tenths.  On  several  occasions,  however,  apples  matured  on  branches  that  experi- 
enced 20°  when  the  buds  were  in  full  bloom. 

"With  Elberta  peach  buds  in  full  bloom,  29°F.  or  above  are  the  safe  tem- 
peratures, because  even  though  occasionally  26,  27,  and  28°  do  no  damage,  yet 
on  most  occasions  28°  will  kill  from  one-fourth  to  one-half.  Twenty-six  degrees 
kills  about  one-half  of  them  and  22°  about  nine-tenths.  Temperatures  as  low 
as  18°  have  failed  to  kill  all  of  them. 

"With  sweet  cherry  buds  in  full  bloom,  30°F.  is  the  safe  temperature;  25,  26, 
27,  28°  have  done  no  damage,  but  29°  usually  kills  about  one-fifth.  Twenty- 
five  degrees  usually  kills  about  one-half,  and  when  the  buds  were  showing  color 
22°  killed  only  two-fifths  of  the  buds. 

"Sour  cherries  are  hardier  than  the  sweet  varieties.  When  the  buds  were 
showing  color  23°F.  did  not  harm  them,  and  when  they  were  in  full  bloom  26° 
killed  about  one-fifth  and  22°  only  two-fifths  of  them. 

"With  apricots,  29°F.  is  the  safe  temperature;  26  and  27°  killed  about  one- 
fifth  and  22°  killed  one-half.      .    .    . 

"The  foregoing  figures  refer  to  the  buds  when  in  full  bloom.     Starting  from 


PROTECTION  AGAINST  FROST 


361 


this  stage,  the  earlier  the  stage  of  development  the  hardier  the  buds  are;  and  in 
general,  when  the  fruit  is  setting  the  injury  is  from  5  to  10  per  cent,  more  than 
when  they  are  in  full  bloom. 

"Sour  cherries  are  the  hardiest,  and  then  follow  in  order  apples,  peaches, 
apricots,  and  sweet  cherries. "2°'* 

Field  observations  sometimes  indicate  that  open  peach  blossoms  are 
more  resistant  than  apple  blossoms  at  the  same  stage. 

At  Different  Stages  of  Blossom  Development. — Table  66  indicates 
that  the  difference  in  tenderness  of  blossoms  at  various  stages  in  their 
development  is  well  recognized.  Table  67,  arranged  from  a  similar  table 
by  West  and  Edlefsen,  shows  experimental  data  that  are,  in  general, 
confirmatory. 


Table  67.— Hardiness  of  Jonathan  Apple  Buds 
ficial  cooling^o^ 

TO  Various  Degrees  of  Arti- 

Date 

Stage  of 
blossom 

Duration  of 
freezing, 
miimtes 

Temperature, 

degrees 

Fahrenheit 

Percentage 
damaged 

April  25 

Full  bloom 
Full  bloom 
Full  bloom 
Full  bloom 
Fruit  setting 
Fruit  setting 
Fruit  setting 
Fruit  setting 
Fruit  setting 
Fruit  setting 
F'ruit  setting 

10 

5 

45 

5 

25 

5 

5 

20 

30 

15 

5 

24.5 
26.5 
27.5 
28.5 
28.0 
25.5 
26.5 
26.5 
27.5 
27.5 
27.5 

52  0 

Apra29 

36  0 

April  25 

54  0 

4pril  29 

0  0 

May  9 

46  0 

May  9 

Mav  9            

93.0 
40  0 

May  10 

May  10 

May  9 

May  9 

22.5 
21.0 
59.0 
62.0 

It  should  be  remembered  that  not  all  the  blossoms  on  a  tree  are  going 
through  the  same  stage  of  development  at  any  given  time  and  the  amount 
of  damage  done  by  a  light  to  moderate  frost  will  depend  to  a  considerable 
extent  on  the  number  of  opened  and  of  unopened  buds.  This  is  shown 
in  Table  68. 

Strawberries  that  are  half  grown,  however,  appear  able  to  stand 
more  freezing  than  the  blossoms. 

Coit"  reports  on  this  fruit:  "Blossoms  are  injured  by  temperatures  below 
30°  at  the  ground  but  young  fruit  endures  temperatures  as  low  as  24°  at  the 
ground  and  28°  in  a  government  shelter  without  injury  and  green  fruit  protected 
by  foliage  endures  temperatures  several  degrees  below  this.  Ripening  fruit 
endures  less  cold,  being  injured  by  temperatures  below  25°  at  the  ground.  A 
good  picking  was  taken  from  Excelsior  plants  Dec.  24,  1903,  although  the  mercury 
had  fallen  at  the  ground  to  22  to  26°  during  10  nights  of  the  month.     Some 


362 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Table  68. — Percentage  of  Open  and  of  Unopened  Blossoms  Killed  by  the 

Freeze  of  Apr.  4,  1908  (24°F.) 

(After  Chandler^^) 


Variety 

Buds  open 

Buds  unopened 

Oldmixon  Free 

Oldmixon  Free 

Elberta  

69.9 
25.4 
24.4 
51.1 

36.6 

15.3 

7.1 

Elberta 

11 

green  fruit  well  protected  with  foliage  survived  January,  1904,  the  mercury  falling 
to  14  at  the  ground  one  night,  16  one  night,  17  two  nights,  18  one  night  and  19 
three  nights;  and  a  few  berries  ripened  during  the  early  part  of  the  month." 

Varietal  Differences. — Varietal  differences  in  hardiness  are  sometimes 
apparent  in  apples. 

In  one  case  in  Missouri  the  greatest  injury  in  Jonathan  seemed  to  be  in  the 
stamens  while  in  Oldenburg  the  pistil  was  damaged.  It  may  be  suggested  that 
this  type  of  injury  might  have  some  interesting  bearing  on  the  pollination  of 
mixed  orchards. 

In  Iowa  many  of  the  Russian  varieties  were  hardier  in  blossom  than  standard 
varieties  in  better  locations.  Similarly  among  the  native  plums  a  freeze  that 
killed  the  ovaries  of  several  varieties  such  as  Rollingstone  which,  incidentally, 
is  very  resistant  to  winter  cold,  injured  only  a  part  of  the  blossoms  of  De  Soto, 
Cheney  and  other  varieties.  These  in  turn  were  surpassed  in  resistance  by  the 
Russian  plums  which  were  said  to  have  been  "less  exposed  than  our  native 
plums. "28  The  Bosc  pear  has  been  reported  as  more  tender  in  blossom  than  the 
other  pears. 2*^  Chandler  states  that  among  peaches  "  the  large  flowered  varieties 
seemed  uniformly  to  be  the  most  hardy,  probably  because  the  petals  remained 
closed  over  the  pistils  longer."^'  This  statement  was  in  reference  to  resistance 
to  frosts  at  blossoming  time;  after  that  period  no  determining  factor  could  be 
found.  Elberta,  tender  at  some  other  stages,  seemed  to  resist  very  late  frosts  as 
well  as  most  varieties. 

Some  varieties  of  strawberry  are  more  susceptible  to  frost  injury 
than  others  because  their  flower  stalks  are  longer  and  more  inclined  to 
raise  the  blossoms  above  the  protection  of  the  leaves.^ 

Schuster"'*  reports  on  the  Ettersburg  No.  121  strawberry:  "The  first  blos- 
soms being  below  the  foliage  are  quite  well  protected  from  ordinary  frost.  Foli- 
age protection  is  quite  a  factor  when  comparing  this  variety  with  other  varieties 
of  hght  fohage,  as  the  primary  blossoms  are  very  apt  to  be  fully  protected  during 
the  frost,  while  the  secondary  blossoms  that  extend  beyond  the  foliage  will 
usually  be  frosted.  Due  to  the  extended  blossoming  period,  it  will  take  repeated 
frosts  to  destroy  the  crop  unless  there  is  a  heavy  freeze." 

Some  interesting  studies  have  been  made  in  an  attempt  to  correlate 
varietal  morphological  peculiarities  with  differences  in  hardiness. 


PROTECTION  AGAINST  FROST  363 

Emery ,^2  in  Montana,  found  injury  in  strawberry  varieties  ranging  from  12 
per  cent,  to  zero.  Tlie  date  of  bloom  in  this  case  seems  to  have  had  little  effect, 
since  Warfield,  one  of  the  earhest  blossoming  of  the  58  varieties  under  observa- 
tion, escaped  all  injury.  Wilcox^i^  at  the  same  station  found  the  anthers  of 
certain  varieties  injured  by  frost;  the  tissue  in  which  the  pollen  grains  were 
embedded  ruptured  and  a  small  proportion  of  the  pollen  grains  were  killed.  Some 
injury  was  observed  in  styles  and  stigmas,  probably  enough  to  interfere  with 
their  functioning.  In  blossoms  which  had  been  fertilized  the  injury  was  confined 
to  the  akenes;  in  no  case  was  the  receptacle  injured.  The  akenes  became  dis- 
colored rapidly.  In  resistant  varieties  they  were  so  deeply  imbedded  in  their 
pits  as  to  be  practically  surrounded  by  the  pulp.  Tender  varieties  had  their 
akenes  most  exposed  or  in  very  shallow  depressions.  Between  these  extremes 
there  was  a  regular  gradation.  It  thus  seems  possible  that  a  variety  may  be 
resistant  at  one  stage — before  fertihzation,  for  example — and  yet  be  tender  at 
another  stage,  say,  after  fertilization. 

Vigor  and  Recuperative  Ability. — The  vigor  of  the  tree  is  stated 
frequently  to  be  a  factor  in  the  damage  produced  by  frost.  This  opinion 
may  be  founded  on  observations  of  the  crop  the  weak  trees  bear  and  in 
failure  to  recognize  that,  frost  or  no  frost,  such  trees  fail  often  to  set  a 
large  percentage  of  fruit.  A  series  of  freezings  of  blossoms  from  strong 
and  from  weak  Gano  apple  trees  indicated  no  superior  hardiness  in  blos- 
soms from  the  more  vigorous;  in  fact  the  average  of  the  various  tests 
was  very  slightly  in  favor  of  the  weak  trees.^^  In  herbaceous  plants, 
injury  sometimes  appears  more  pronounced  in  those  making  a  less 
vigorous  growth,  but  in  all  probability  the  observed  difference  is  due 
to  the  superior  recuperative  powers  of  the  more  vigorous  plants.  There 
is  some  indication  that  plants  treated  with  nitrate  of  soda  recover  from 
frost  damage  better  than  others.  This  recovery  is,  however,  in  the  vege- 
tative portions.  There  is,  occasionally,  a  fairly  large  second  bloom  on 
apple  and  pear  trees  following  a  frost,  but  this  is  the  exception  and  ap- 
parently it  is  not  related  to  vegetative  vigor.  Recuperative  power  is  of 
little  immediate  benefit  to  the  grower  once  the  blossoms  are  killed. 

Weather  Conditions  Before  and  After  Freezing. — The  weather  pre- 
ceding and  immediately  following  the  freeze  may  be  factors  of  some 
little  impoi'tance. 

Pf offer'",  speaking  of  plant  tissues  in  general,  says:  "The  resistance  to 
cold  depends  to  a  certain  extent  upon  the  present  and  previous  external 
conditions.  Thus  Haberlandt  found  that  seedUngs  grown  at  18°  to  20°C. 
froze  more  readily  than  those  grown  at  8°C."  Rosa^'^^  found  that  cabbage 
grown  in  a  greenhouse  at  20°C.  killed  when  exposed  to  -4°C.  for  1  hour 
while  plants  grown  in  a  cold  frame  were  uninjured  by  exposure  to  _the  same 
temperature  for  over  2  hours.  It  seems  reasonable  to  suppose  that  the 
same  principle  applies  to  fruit  blossoms.  Garcia''^  records  that  a  temperature 
of  24.75°F.  at  2  a.m.  followed  by  a  rise  to  31°  at  5:30  caused  less  than  3  per 
cent,  injury  to  Alexander  peach  blossoms  which  were  in  full  bloom  at  the  time, 


364  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

though  in  other  instances  considerable  damage  followed  a  temperature  of  25.5°. 
It  should  be  recalled  that  there  is  practical  unanimity  among  investigators  that 
rapid  thawing  is  not  in  itself  injurious,  but  there  is  no  evidence  as  to  the  effects 
of  Hght  on  frozen  tissue.  Light  is  known  to  increase  permeability  and  may  well 
be  conceived  to  prevent  the  return  to  the  cells  of  water  which  has  been  withdrawn 
upon  freezing,  thus  causing  injury  to  tissues  which  otherwise  would  recover 
their  normal  state.  The  common  conviction  among  practical  horticulturists 
that  rapid  thawing  is  injurious  may  be  founded  on  observations  of  the  effect 
of  light  on  frozen  tissue.  Furthermore,  the  effects  of  the  duration  of  exposure  to 
a  given  temperature  have  not  been  established  definitely. 

Signs  of  Damage. — The  thermometer,  evidently,  frequently  fails  to 
give  close  or  reliable  indication  of  the  amount  of  damage  a  frost  has 
inflicted.  A  fairly  close  estimate  may  be  made,  ordinarily,  late  in  the 
forenoon  following  a  freeze,  by  an  examination  of  the  buds  themselves. 

The  pistils  are  the  parts  most  readily  affected  in  the  blossom,  becoming,  when 
damaged,  wilted  and  discolored,  though  the  bud  may  unfold  its  petals  and 
stamens.  Curiously,  in  April,  1920,  at  Columbia,  Mo.,  a  temperature  of  14°F. 
when  Jonathan  apple  blossoms  were  fairly  well  advanced  seemed  to  damage,  not 
the  pistils,  but  the  stamens  which  turned  orange  in  color,  and  the  effects  also  be- 
came evident  on  the  stems  near  the  purse.  A  similar  condition,  though  less 
pronounced,  has  been  observed  in  the  Willamette  valley  in  Oregon.  Sometimes 
the  petals  are  dwarfed  but  the  bud  otherwise  uninjured.  In  peaches  advanced 
beyond  the  blossoming  stage.  Chandler^*  states  that  the  veins  surrounding  the 
seed  are  the  most  tender,  followed  in  order  by  the  kernel  and  the  flesh.  Chandler 
suggests  that  the  greater  tenderness  of  the  seed  may  be  correlated  with  the  differ- 
ence in  sap  density.  The  young  seeds  of  the  apple  seem  particularly  tender  and 
after  a  frost  they  frequently  are  brown  while  the  flesh  is  apparently  undamaged. 

Paddock  and  Whipple^^^  state  that  after  fertihzation  has  occurred  apple 
blossoms  may  survive  some  injury  to  the  seeds  though  blossoms  of  the  stone 
fruits  frozen  to  the  extent  that  the  basal  part  of  the  pistil  is  damaged  rarely  set 
fruit.  When  interior  apple  tissues  outside  the  seed  cavities  are  damaged  the 
fruit  does  not  mature.  In  this  particular  case,  they  say,  the  injury  becomes 
apparent  early,  in  a  yellowing  of  the  tissues  around  the  stem  end  of  the  fruit. 
Seedless  apples,  particularly  of  some  varieties,  frequently  develop  to  maturity 
but  generally  are  somewhat  smaller  than  those  with  seeds.  The  same  writers 
state  that  the  pear  will  mature  fruit  after  showing  still  more  injury  than  the 
apple.  In  the  young  fruit  they  find  much  the  same  conditions  holding,  though 
the  stone  fruits  are  said  not  to  show  injury  which  is  confined  to  the  seed  cavity 
until  the  time  of  the  final  swelling  just  before  ripening,  when  the  injured  fruit 
will  show  gummy  exudations  and  ripen  abnormally  or  it  may  drop  before  ripen- 
ing. When  the  injury  ismoreextensivethey  drop  shortly  after  blossoming.  Apples 
and  pears  survive  injury  to  the  seeds  alone  and  in  most  cases  with  no  other  visible 
evidence  of  damage.  Apples  injured  outside  the  seed  cavity  do  not  mature  but 
pears  so  injured  develop  abnormally  through  enlargement  of  what  would  ordi- 
narily be  the  neck  of  the  fruit.  This  enlargement,  together  with  the  retarded 
development  of  the  parts  surrounding  the  core,  results  in  the  familiar  "  bullneck." 


PROTECTION  AGAINST  FROST  365 

Injury  to  pear  flesh  apparently  must  extend  well  away  from  the  core  to  prevent 
the  development  of  the  fruit,  though  it  conceivably  may  interfere  to  some  extent 
with  the  so-called  "secondary  effect"  of  pollination. 

Impaired  germination  of  pollen  of  pear,  plum,  cherry  and  peach  on 
exposure  for  6  hours  to  a  temperature  of  —  1.5°C.  has  been  reported. ^^^ 
Chandler^*  found  that  pollen  of  the  Jonathan  apple  after  exposure  to 
—  3°C.  showed  a  germination  of  33  per  cent,  as  compared  with  84  per 
cent,  for  unfrozen  pollen,  and  pollen  of  the  Cillagos  apple  frozen  for 
30  minutes  at  —  8°C.  germinated  25  per  cent,  as  compared  with  67  per 
cent,  for  unfrozen. 

Frost  Injury  and  the  Size  of  the  Crop. — Finally  it  must  be  considered 
that  the  damage  from  a  given  frost  is  a  varying  quantity.  Some  peach 
trees  on  which  1,000  peaches  would  be  a  good  crop  bear  20,000  or  more 
fruit  buds.  Obviously,  with  other  conditions  favorable,  a  loss  of  80 
per  cent  of  the  buds  would  not  interfere  with  the  production  of  a  full 
crop  and  in  a  commercial  sense  this  frost  would  not  prove  damaging. 
If,  however,  the  same  trees  were  bearing  only  8,000  buds  a  loss  of  80  per 
cent  might  become  a  serious  matter. 

It  should  be  apparent  that  no  set  rules  of  procedure  as  governed  by 
observed  temperatures  can  be  given.  Probably  the  safest  course  for  the 
grower  when  freezing  occurs  is  to  try  to  keep  the  temperature  above 
29°F.  if  he  is  heating  his  orchard  and  after  a  frost  it  is  best  to  proceed  on 
the  assumption  of  a  full  crop  unless  the  evidence  to  the  contrary  is 
convincing. 

AVOIDING  FROST  THROUGH  LATE  BLOSSOMING  VARIETIES 

The  relatively  wide  range  in  blossoming  dates  of  the  many  kinds  and 
varieties  of  fruits  is  often  important  in  determining  the  relative  danger 
from  frost  to  an  orchard  on  a  given  site.  Conversely,  the  blossoming 
dates  should  have  bearing  on  the  decision  as  to  the  type  of  fruit  to  be 
planted.  On  a  very  large  scale  the  limiting  factor  in  the  growth  of 
apricots  and  almonds  is  not  their  lack  of  hardiness  to  winter  cold,  since 
some  varieties  are  probably  as  hardy  as,  or  even  hardier  than,  the  peach, 
but  rather  their  extremely  early  blooming. 

Blossoming  Range  Varies  with  Earliness. — The  earlier  the  average 
date  of  blossoming  in  any  section  the  longer  is  the  spread  of  the  ordinary 
season  of  bloom.  In  the  north  the  time  between  the  first  peach  and  the 
last  apple  to  blossom  is  frequently  shorter  than  the  interval  in  the  south 
between  the  first  and  the  last  peach.  Consequently  the  relative  earliness 
or  lateness  in  blossoming  of  a  variety  may  be  more  important  in  some 
regions  than  in  others.  Table  69  shows  the  difference  between  peaches 
and  apples  in  the  number  of  times  heating  might  be  necessary  at  various 
places  in  Utah.     The  difference  between  a  total  of  263  heatings  for  the 


366 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Table  69. — Number  of  Heatings  Necessary  to  Protect  Utah  Orchards 
{After  West  and  Edlefsen'^°'') 


County 

Number 
of  years 

Peach 

Apple 

Apricot 

Cherry 

Utah  (Prove) 

16 
16 
14 
16 
13 
16 

93.0 
28.0 
32.0 
36.0 
66.0 
8.0 

46.0 

13.0 

8.0 

15.0 

4.0 

3.0 

45.0 

45.0 
3.2 

Provo  Bench 

Box  Elder  (Corinne) 

Salt  Lake  (Salt  Lake).... 
Weber                      

21.0 

Cache                 

Totals 

263.0 
2.9 

89.0 
0.97 

21.0 

Average  per  year 

1.5 

peaches  and  89  for  the  apples  would  make  a  considerable  item  in  the 
cost  of  production.  In  addition,  the  later  blooming  fruit  is  not  only- 
likely  to  encounter  fewer  frosts  but  such  as  it  does  encounter  are  likely 
to  be  less  severe.  Finally,  it  should  be  recalled  that  the  later  stages  of  a 
blossom's  development  are  the  most  tender;  for  this  reason  also  a  given 
frost  is  likely  to  damage  the  early  variety  more.  This  double  effect  is 
well  shown  in  Table  70. 

Table  70. — Percentage  op  Peach  Blossoms  Killed  by  Temperature  of  28°F. 
(After  Garcia''^) 


Varieties 


Fruits  just 
setting 


Freshly  opened 
flowers 


Buds  about  to 
open 


Elberta 

Crothers 

Salway 

Texas  King .... 
Hynes'  Surprise 
Alexander 


This  table  shows  that  for  blossoms  just  setting  fruit  there  was  not 
enough  difference  to  indicate  any  varietal  superiority  in  hardiness.  How- 
ever, Elberta,  Crothers  and  Salway  blossoms  were  all  at  the  most  ad- 
vanced stage  which  is  very  tender.  The  three  other  varieties  had  a 
considerable  number  of  blossoms  less  advanced  at  the  time  of  the  freeze 
so  that,  despite  a  rather  large  percentage  of  killing,  the  fruit  of  these 
varieties  had  to  be  thinned,  while  the  first  three  varieties  bore  very  little, 
Elberta  in  fact  bearing  none  at  all. 

Table  71is  based  on  the  Mikesell  data,"^  with  additions.  Though  computed 
rather  arbitrarily  it  shows  in  a  general  way  the  relative  susceptibility  to  frost 


PROTECTION  AGAINST  FROST 


367 


Table  71. — Date  of  First  Blossoms  Relative  to  Last  Minimum  of  29°F.  at 
Wauseon,  Ohio,  for  30  Years 


Blossoming  relative 
to  frost 


Apple. 

Pear. 

Peach, 

Plum, 

Cherry, 

Grape, 

Straw- 
berry, 
years 

years 

years 

years 

years 

years 

years 

8 

13 

12 

14 

0 

10 

22 

19 

14 

17 

15 

26 

16 

10 

13 

13 

15 

15 

0 

20 

17 

14 

14 

14 

26 

5 

12 

12 

11 

14 

0 

25 

18 

15 

18 

15 

26 

Red 
rasp- 
berry, 
years 


Type  variety: 

Before 

After 

Early  variety: 

Before 

After 

Late  variety: 

Before 

After 


at  Wauseon  of  the  fruits  under  observation  there  (see  Tj'pe  fruits).  In  addition 
an  attempt  is  made  to  show  how  earher  or  later  blossoming  varieties  of  the  respec- 
tive fruits  would  have  been  affected.  A  somewhat  artificial  method  was 
necessary.  Taking  as  guide  the  average  blossoming  dates  of  various  fruits  at 
Geneva,  N.  Y.,^°  the  varieties  studied  in  Table  70  were  interpolated  and  the 
differences  between  their  average  dates  of  blossoming  at  Geneva  and  that  of  the 
earliest  and  latest  blossoming  common  varieties  grown  there  were  used  in  the 
Wauseon  figures.  Thus  the  apple  was  figured  on  the  basis  of  Gravenstein  being 
2  days  earUer  in  blossoming  than  the  type  variety  (King).  The  Bartlett  pear 
was  fitted  into  the  New  York  tables  on  the  assumption  that  it  blossomed  with 
Clapp  Favorite  and  Angouleme;  Anjou  and  Vermont  Beauty  were  the  extremes, 
2  days  earUer  and  later  respectively.  The  plum  (variety  not  stated)  was  placed 
in  the  middle  of  the  Domestica  group. 

The  table  should  not  be  taken  too  literally  as  it  is  constructed  on  such  arbi- 
trary assumptions  (including  the  temperature  selected  as  injurious).  Neverthe- 
less it  shows  quite  clearly  the  respective  chances  of  frost  damage  to  different 
fruits  at  a  given  spot  in  northern  latitudes  and  in  a  measure  the  relative  import- 
ance of  early  and  late  blossoming  varieties  which  is  much  greater  in  some  fruits 
than  in  others.  Furthermore,  it  should  be  understood  clearly  that  the  blossoming 
dates  of  all  kinds  and  varieties  of  fruits  have  a  much  wider  spread  in  milder 
cUmates  than  that  of  the  northeast  and  these  differences  are  much  greater  and 
more  important  in  these  regions. 

Figure  36  shows  the  blossoming  dates  of  certain  fruits  in  relation  to 
the  last  spring  temperature  of  27°F.  at  a  point  in  southern  Utah.  In  no 
year  did  the  apricot  or  the  almond  blossom  after  the  last  temperature  of 
27°,  and  in  no  case  did  the  Yellow  Transparent,  generally  a  rather  early 
blossoming  apple,  bloom  before.  Between  these  extremes  lie  the  Elberta 
peach,  which  blossomed  after  the  last  27°  temperature  in  2  years  out  of 
the  8  represented,  and  the  German  prune  which  preceded  it  in  1  year 
out  of  6  recorded.  The  likelihood  of  damage  or  safety  from  frost  is  this 
locality  quite  evidently  depends  on  the  kind  of  fruit  chosen,  more  so 


368 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


than  in  sections  where  the  blossoming  season  has  less  spread.  At  Geneva, 
N.  Y.,  the  average  interval  from  the  first  peach  blossom  to  the  last 
apple  tree's  first  bloom  is  15  days.  However,  there  are  unquestionably 
years  in  almost  any  fruit  growing  region  when  the  blossoming  period 
actually  determines  the  difference  between  a  full  or  a  partial  crop — or  a 
crop  failure. 


Fig.  36. — Frost   susceptibility   of   several   fruits   as   determined    by   date    of   blossoming. 
{After  Ballantyne^^) 

Blossoming  Period  and  Fruit  Bud  Position. — In  addition  to  varietal 
difference  in  blossoming  season  there  is  occasionally  some  diversity  within 
the  variety.  There  is  a  tendency,  though  it  is  by  no  means  constant,  for 
vigorous  trees  to  blossom  somewhat  later;  sometimes  the  interval 
between  vigorous  and  weak  trees  is  2  to  3  clays.  Terminal  and  lateral  fruit 
buds  of  apple  frequently  are  several  days  behind  the  spur  fruit  buds  in 
opening;  in  at  least  one  instance  Jonathan  trees  have  lost  practically  all 
the  spur  blossoms  from  frost  and  still  returned  a  partial  crop  from 
their  terminal  buds.  The  outer  buds  on  long  twigs  and  all  buds  on  short 
twigs  in  peaches  are  the  first  to  open  and  the  slight  difference  in  develop- 
ment of  these  and  the  basal  blossoms  on  the  same  trees  has  made  at  times 
a  vast  difference  in  the  crop  borne  in  respective  zones. ^^ 

Retarding  Blossoming. — Attempts  at  retarding  fruit  blossoms  so  they 
will  escape  a  certain  amount  of  exposure  to  frost  have  not  proved  success- 
ful on  a  commercial  scale.  Whitewashing  the  branches  to  reduce  the 
amount  of  heat  absorbed  from  sunlight  has  been  discussed  previously; 
shading  has  been  shown  to  have  only  a  very  limited  application.  Despite 
abundant  evidence  to  the  contrary  the  notion  persists  that  mulching 
retards  the  opening  of  fruit  buds.  Except  for  fruits  whose  tops  are 
covered,  as  strawberries,  it  is  of  no  value. 


PROTECTION  AGAINST  FROST 


369 


If  late  blooming  is  urgently  needed  it  is  best  secured  by  selecting  late 
blossoming  varieties,  planting  them  on  a  north  slope  and  keeping  them 
growing  vigorously.  The  last  two  measures  are  effective  only  within 
comparatively  narrow  limits,  leaving  the  first  as  the  best  method  of 
evading  frost  damage.  In  certain  fruits  the  present  varietal  range  in 
blossoming  season  is  hardly  sufficient  to  secure  protection  through  the 
selection  of  the  later  blooming  sorts,  but  in  others  practical  immunity 
from  damage  may  be  obtained  in  that  way.  There  is  reason  to  believe 
that  late  blooming  varieties  of  many  fruits  may  be  bred  and  the  ultimate 
solution  of  the  frost  problem  lies  in  that  direction. 

Indices  to  Blossoming  Periods  in  New  Location. — Sometimes  in 
considering  locations  where  fruit  has  not  been  grown  it  is  desirable  to 
know  at  what  time  the  trees  may  be  expected  to  bloom.  It  is  possible 
that  phonological  observations  on  native  plants  in  different  sections 
would  show  a  degree  of  correspondence  with  the  various  fruits  so  that 
certain  native  plants  might  serve  as  indicators  of  what  fruit  trees  would 
do  in  the  same  locality. 

Figure  37,  arranged  from  the  Mikesell  Records, '^^  shows  the  overlapping  of 
the  King  apple  in  the  stage  from  first  blossom  to  full  bloom  with  poison  ivy,  a 


1884. 

"IT 

_■_ 

"_. 

TIT 

13= 

E^ 

^^ 







:^T^= 



1886 

_•=: 

=-=: 



. 

._- 

_ 

3^; 

l»8g 









— 

■" 

— 

1890 

_ 

__ 



— ; 

rzir" 

r:_ 











1 

loyi! 





-- 



■=-= 

■=— 









;rr: 



IB  94 





_ 



IBSfa 





__ 

. 



^ 

_ 

_  _ 

1 

_  - 





— 

— 

1898 



'-^-z 

-:3d 

1 — 



poisoh/iv 

Y 

1893 

-T- 



\-~. 

— 

r 

—A 

PP 

-F- 

?0  IZ  24   Z6    ?8    JO    2     4     6     8     10    \Z    14    IG    IS    20    22 
April  f^  a  y 

Fig.  37. — Comparable  phenological  stages  in  apple  and   poison  ivy.      (Apple  from  first 
blossom  to  full  bloom;  poison  ivy  from  starting  of  buds  to  first  fully  formed  leaf). 


fairly  common  wild  plant,  in  the  stage  from  buds  starting  to  the  first  fully  formed 
leaf.  It  will  be  observed  that  the  correspondence,  though  not  invariable,  is 
rather  close.  Some  plants  show  better  correspondence  with  the  King  apple  than 
others;  several  recorded  in  the  Mikesell  records  show  less  than  the  poison  ivy. 
This  instance  is  but  suggestive  of  many  other  parallels  or  overlappings  in 
blossoming  seasons  that  may  be  estabhshed— parallels  that  in  many  cases  would 
repay  careful  study. 


FROST  PREDICTION 

It  is  frequently  important  to  know  a  few  hours  in  advance  whether 
or  not  a  frost  will  occur,  so  that  final  preparations  for  protection  against 

24 


370  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

its  effects  may  be  made.  In  a  general  way  frost  may  be  looked  for  on  a 
clear,  still  night;  clear,  because  it  favors  radiation,  still,  because  the  cooled 
air  is  not  mixed  with  the  warmer  air.  These  conditions  are  associated 
with  high  barometric  pressure.  However,  they  do  not  always  produce 
frost  and  a  closer  estimate  is  desirable. 

Relation  of  Dewpoint  to  Minimum  Temperature. — Until  recently  the 
dewpoint  as  determined  in  late  afternoon  or  early  evening  has  been 
considered  to  mark  the  minimum  temperature  for  the  following  morning. 
Air  contains  varying  percentages  of  moisture;  the  higher  the  tempera- 
ture the  more  it  can  carry  as  vapor.  If  any  given  sample  of  air  is  cooled 
the  point  is  reached  ultimately  where  some  of  the  moisture  is  deposited. 
This  is  the  dewpoint.  The  condensation  of  moisture  releases  heat  to  the 
air  and  it  was  thought  that  the  heat  thus  released  was  sufficient  to  prevent 
any  further  drop  in  temperature  and  that  the  evening  dewpoint  therefore 
marked  the  minimum  for  the  following  morning. 

Careful  comparison  of  indicated  and  actual  temperatures  has  shown, 
however,  that  the  afternoon  or  evening  dewpoint  alone  is  not  a  suffi- 
ciently reliable  indicator  to  be  of  any  great  value  in  predicting  the 
minimum  for  the  following  morning.  In  fact  Cox^^  records  a  slight  degree 
of  frost  with  the  humidity  at  100  per  cent.  Ordinarily,  however,  it  may 
be  assumed  that  when  the  evening  relative  humidity  is  from  40  to  50 
per  cent.,  the  ensuing  minimum  temperature  on  a  characteristic  radiation 
night  will  be  very  close  to  the  evening  dewpoint;  when  the  evening  relative 
humidity  is  below  40  per  cent  the  minimum  will  average  5°  above  the 
evening  dewpoint;  with  evening  relative  humidities  above  50  per  cent 
the  minimum  temperatures  will  be  below  the  evening  dewpoint. 

Little  reliance  can  be  placed  on  the  afternoon  maximum  alone  as  an 
indicator  unless  it  is  very  high  indeed.  No  maximum  below  75  or 
76°F.  should  be  regarded  as  a  guarantee  against  frost  the  following  morning. 

Weather  Bureau  Methods. — At  present  no  one  method  of  predicting 
minimum  temperatures  is  in  use  by  Weather  Bureau  officials  throughout 
the  country.  Local  conditions  apparently  make  a  certain  method  fit 
closely  at  one  point  while  at  another  point  it  gives  less  satisfactory  results. 
It  seems  probable  that  observations  extending  over  at  least  2  years  for 
each  section  should  be  accumulated  and  the  data  studied  to  determine 
which  method  will  give  the  closest  approximation  in  future  predictions. 

Smith^*-  has  devised  several  methods  and  applied  them  to  data  from  different 
points.  The  simplest,  perhaps,  is  the  so-called  median  temperature  method. 
This  is  based  on  the  assumption  that,  in  weather  characteristic  of  most  spring 
frosts,  the  "radiation  nights,"  clear  and  rather  still,  the  temperature  falls  practi- 
cally at  a  uniform  rate  from  a  maximum  in  the  afternoon  to  a  minimum  in  the 
morning  and  that  the  times  of  maximum  and  minimum  temperatures  will  be 
the  same  for  all  such  days.  The  average  time  of  the  median,  half  way  between 
the  times  of  the  maximum  and  of  the  minimum,  is  ascertained  from  previous 


PROTECTION  AGAINST  FROST  371 

records  of  the  particular  station.  A  thermometer  reading  at  this  median  time, 
subtracted  from  the  afternoon  maximum,  gives,  presumably,  half  the  total 
fall  in  temperature  to  be  expected.  Thus  if  the  maximum  were  70°F.,  the 
median  temperature  50°,  the  difference,  20°,  taken  from  the  median  temperature, 
would  indicate  the  expected  minimum  to  be  30°.  Under  conditions  obtaining 
at  some  stations  this  method  seems  the  most  reliable  that  has  been  tried. 
In  general  it  seems  to  give  closer  approximations  to  actual  temperatures  in 
regions  of  very  low  humidity,  not,  perhaps,  because  the  method  works  better 
there  than  elsewhere,  but  possibly  because  the  other  methods  do  not  work  so 
well.  As  indicated  by  Hallinbeck,  with  certain  precautions  in  its  application 
it  seems  to  work  well  at  Roswell,  New  Mexico.  Wherever  compared  with 
the  older  method  of  assuming  identity  between  evening  dewpoint  and  morning 
minimum  it  has  proved  superior. 

Still  more  accurate  predictions  were  found  possible  in  Ohio  by  Smith,  using 
the  equation  y  =  a  -\-  bR,  where  R  is  the  evening  relative  humidity,  y  the  varia- 
tion of  the  morning  minimum  temperature  from  the  evening  dewpoint,  while  a 
and  b  are  constants  derived  from  previous  data  accumulated  at  points  with  like 
conditions.  This  linear  equation,  when  plotted,  fitted  the  Ohio  data  very  satis- 
factorily, but  charts  from  certain  other  points  were  fitted  more  closely  by  a 
parabola  whose  equation  was  modified  by  Smith  to  read  v  =  x  +  by  -\-  cz  in 
which  X,  y  and  z  are  coefficients  to  be  determined  from  previous  data,  b  the  eve- 
ning relative  humidity,  c  the  square  of  the  relative  humidity  and  v  the  variation 
of  the  minimum  temperature  of  the  following  morning  from  the  evening  dew- 
point.  The  value  found  for  v  is  added  to  or  subtracted  from  the  evening  dew- 
point  and  the  minimum  temperature  indicated. 

The  method  of  obtaining  the  constants  is  explained  in  detail  in  Supplement 
16  of  the  Monthly  Weather  Review.  As  has  been  suggested  above,  the  constants 
vary  with  the  locality.  As  samples,  the  following  may  be  cited:  for  the  y  =  a 
+  bR  equation,  at  Lansing,  Mich.,  a  =  —11.2,  b  =  0.727,  at  Grand  Junction, 
Col.,  a  =  —7.01,  b  =  0.53;  for  the  v  =  x  -\-  cz  -\-  by  equation,  Modena,  Utah 
(all  nights,  radiation  or  otherwise),  x  =  7.3,  y  =  0.18,  z  =  0.0057;  for  Montrose, 
Col,  X  =  -22.0,  y  =  0.383,  z  =  0.01167. 

The  first  equation  has  been  found  to  give  satisfactory  results  at  some  places, 
the  second  has  proved  preferable  at  others;  as  stated  above,  the  median  tempera- 
ture method  seems  best  here  and  there,  while  in  some  cases  still  other  me'thods 
are  used.  Sometimes  a  mean  between  results  secured  by  two  methods  has 
proved  more  nearly  accurate  than  either  singly.  One  disadvantage  of  the 
median  temperature  method  as  compared  with  the  others  outlined  here  lies  in 
the  fact  that  the  forecast  cannot  be  made  until  several  hours  later  than  is  possible 
from  the  metheds  based  on  hygrometric  data.  The  fact  that  different  methods 
fit  various  places  is  probably  an  expression  of  the  differences  in  topography  and 
in  humidity,  relation  to  centers  of  high  pressure  and  other  factors  somewhat 
pecuhar  to  particular  locaUties  but  all  combining  in  frost  production. 

It  should  be  borne  in  mind  also  that  the  methods  outlined  fit  only 
radiation  nights  and  that  occasionally  fruit  blossoms  are  damaged  by 
cold  in  other  ways  such  as  high  cold  winds  or  cold  snow  squalls.  To 
forecast  these,  reliance  must  be  placed  in  the  weather  map.     The  problem 


372 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


is,  in  any  case,  sufficiently  complex  to  warrant  the  grower  who  wishes 
reliable  forecasts  in  trying  to  secure  them  from  the  nearest  station  of  the 
Weather  Bureau,  either  directly  or  by  corrections  from  forecasts  made 
for  some  noar])y  point. 

Local  Interpretation  of  "Key  Station"  Predictions. — It  will  be  under- 
stood, considering  the  local  differences  in  temperature,  that  the  general 
forecast  may  require  correction  for  the  grower's  own  site.  The  forecast, 
as  issued,  is  based  upon  observations  from  sheltered  instruments  at 
a  certain  spot;  yet  it  is  given  out  necessarily  to  cover  a  wide  radius  of 
territory  where  local  differences  may  be  considerable.  Districts  that 
are  well  organized  for  frost  fighting  have  several  "key  stations"  for  which 
the  forecasts  are  corrected  individually.  Even  in  such  cases,  however,  it 
may  be  necessary  to  make  discriminating  corrections  if  the  probable 
minimum  for  a  given  spot  is  to  be  determined. 

Table  72  shows  minimum  temperatures  on  cold  spring  mornings  at  5.5 
feet  and  0.5  foot  elevations  at  three  spots  in  the  village  of  Williamstown,  Mass. 
Station  A  is  a  shelter  thermometer  and  may  be  considered  the  "key  station." 
It  is  of  interest  to  see  how  predictions  for  the  key  station  would  apply  to  straw- 
berries at  Station  7.  As  is  shown  in  the  last  column  of  the  table  the  difference  is 
variable  but  always  considerable,  under  conditions  favorable  to  frost.  As 
Milham,!^^  from  whose  data  the  table  is  taken,  states,  it  is  not  a  difference  due 
to  site  alone;  in  adapting  the  forecast  for  Station  A  to  vegetation  at  Station 
7  allowances  must  be  made  as  follows:  2°  for  the  deviation  between  sheltered 
and  exposed  thermometers,  3°  for  the  inequality  in  height  of  the  two  thermome- 
ters above   ground  and  6°  for  the  difference  in  site.     These  together  indicate  a 


Table  72. — Minimum  Temperatures  at 

Williamstown 

,  Mass. 

134 

Date 

Station  A 
(.shelter) 

Station  1 

Station  8 

Station  7 

Difference, 
Station  A 
and  lower  7 

Upper 

Lower 

Upper 

Lower 

Upper 

Lower 

1907 
April  27 

32 
33 
38 
27 
42 
37 
39 
33 
37 

40 
39 
3.5 
42 
46 
39 
42 
40 

29 
36 
25 
41 
35 
38 
31 
36 

38 
37 
33 
30 
45 
39 
40 
39 

30 
28 
34 
24 
40 
35 
38 
30 
36 

38 
36 
33 
30 
44 
39 
40 
39 

30 
28 
32 

39 
34 
36 

34 

37 
35 
31 
28 
43 
38 
38 
39 

27 
25 
32 

36 
32 
34 

32 

36 
32 
30 
27 
39 
37 
36 
37 

27 
25 
31 
18 
33 
34 
36 
25 
31 

35 
31 
31 

28 
40 
38 
36 
36 

23 
21 
27 
15 
31 
31 
33 
20 
31 

34 
28 
27 
24 
35 
38 
34 
34 

9 

May     1 

May    5   

May  11 

May  12 

May  20 

12 
11 
12 

6 

May  21 

6 

May  24             

13 

May  28 

6 

1908 
April  29 

6 

May     1 

May     3    

11 
8 

May    4 

May    5 

May    9            .... 

18 
11 
1 

May  10 

May  14 

8 
6 

PROTECTION  AGAINST  FROST  373 

total  of  11°  which,  it  is  evident  from  the  table,  was  realized  frequently.  Though 
it  is  unsafe  to  generalize  from  a  few  observations,  it  is  interesting  to  note  that 
for  the  lower  temperatures  at  Station  A  the  departures  for  Station  7  averaged 
greater  than  they  did  for  the  higher  temperatures  at  Station  A ;  in  other  words  it 
would  seem  that  as  the  temperature  at  Station  A  came  nearer  to  the  freezing 
point  the  temperature  at  Station  7  was  in  even  greater  measure  more  likely 
to  drop  below  that  point.  Evidently  a  strawberrj^  grower  at  Station  7  should 
deduct  at  least  11°  from  the  minimum  indicated  for  Station  A  to  forecast  the 
probable  temperature  at  his  own  place;  if  apples  were  the  crop  at  the  same  point 
the  deduction  would  be  somewhat  less. 

Even  greater  differences  are  reported  by  Cox''"  between  minima  on  the  bog 
at  Mather,  Wis.,  and  the  minima  at  the  "key  station"  La  Crosse,  55  miles  away. 
Shelter  minimum  temperatures  on  the  upland  at  Mather  for  May,  1907,  averaged 
3.8°  below  those  at  La  Crosse  with  ranges  from  —14°  to  +8°;  minima  at  5 
inches  above  the  bog  at  Mather  averaged  —8.5°  below  those  for  La  Crosse, 
with  ranges  from  —20°  to  +5°.  Cox  states  that  the  average  difference  when  the 
weather  is  clear  and  the  pressure  high  is  about  18°,  so  that  in  such  weather  a 
minimum  of  50°  for  La  Crosse  signifies  a  bog  minimum  at  Mather  of  about  32°. 

The  grower  who  wishes  to  prophesy  with  accuracy  what  the  minimum 
will  be  in  his  own  orchard,  bog  or  field  must  rely  on  the  Weather  Bureau 
to  furnish  information  as  to  the  probable  minimum  at  some  fixed  point 
and  he  must  rely  on  himself  to  adapt  these  indications  to  the  spot  where 
his  own  crop  is  located.  To  do  this  it  will  be  necessary  to  keep  accurate 
records  of  minima  at  his  own  orchard  on  all  clear  nights  during  the  spring 
for  2  or  3  years,  to  compare  them  with  the  records  of  the  Weather  Bureau 
and  from  these  data  to  determine  the  probable  and  the  safe  corrections 
to  be  made. 

FROST  FIGHTING 

The  data  already  discussed  show  that  much  can  be  accomplished  in 
combatting  frost  by  selection  of  site,  fruit  and  variety  and  in  some  cases 
by  cultural  practices.  All  these  measures  may  be  regarded  as  preventive. 
There  remain  for  consideration  the  palliative  measures. 

Smoke  Screens  to  Reduce  Radiation. — In  view  of  the  emphasis  placed 
on  radiation  as  a  factor  under  frost  conditions,  efforts  to  prevent  heat 
loss  through  radiation  might  be  expected  to  be  fruitful.  In  fact  it  is 
rather  generally  assmned  that  a  dense  smoke  will  so  retard  radiation 
losses  that  frost  damage  will  be  checked  or  prevented.  Such  cases  have 
been  recorded.  However,  quantitative  data  available  for  comparison  of 
temperatures  in  smudged  areas  where  the  heating  factor  is  eliminated 
with  those  in  unsmudged  and  unheated  areas  do  not  indicate  a  sufficient 
saving  of  heat  to  make  the  smudge  in  itself  of  any  great  value.  Table  73 
shows  temperatures  in  a  smudged  area  and  in  an  unsmudged  area  adja- 
cent, in  a  German  vineyard.  The  averages  include  some  figures  not 
presented  here. 


374 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Table  73. — Temperatures  in  Smudged  and  Unsmudged  Areas^^s 
(Degrees  Centigrade) 


Hour 

Temperature 

Smudged 

Unsmudged 

10:30 

+2.01 

+  1.87 

11:30 

+  1.53 

+  1.40 

12:30 

+0.78 

+0.62 

1:30 

+0.13 

+0.07 

2:30   * 

-0,73 

-0.50 

3:30 

-0.90 

-0.95 

4:30 

-1.14 

-1.25 

5:30 

-0,05 

-0.03 

0,098 

0.042 

The  differences  are  at  the  most  too  small  to  be  of  practical  impor- 
tance. It  was  suggested  that  the  small  difference  was  due  to  air  move- 
ment and  the  investigator  appears  not  to  have  been  convinced  that 
greater  differences  might  not  be  found  under  other  conditions. 

Kimball  and  Young/"^  using  a  pja-ogeometer,  measured  the  radiation 
in  smudged  and  in  unsmudged  areas  in  California  and  Oregon,  finding 
decreases  by  smudging  from  0.110  and  0.115  calories  per  minute  per 
square  centimeter  to  averages  of  0.098  and  0.103  respectively  in  Cali- 
fornia and  in  Medford,  Oregon,  from  0.109  to  an  average  of  0.099.  Con- 
siderable fluctuation  under  the  smoke  occurred,  the  maximum  decrease 
amounting  to  28  per  cent,  with  averages  respectively  of  11,  10  and  9 
per  cent.  They  conclude  from  their  investigations  that  "the  retardation 
of  nocturnal  radiation  by  the  smoke  cloud  plays  an  insignificant  part  in 
frost  protection." 

The  reflection  of  heat  from  smoke  clouds  is  evidently  very  small. 
Miiller-Thurgau^^^  points  out  that  smoke  differs  in  its  composition  from 
clouds.  It  should  be  recalled  that  radiation  is  constantly  occurring, 
clouds  or  no  clouds,  and  that  they  do  not  prevent  radiation  but  only 
reflect  heat,  and  since  outgoing  and  incoming  heat  approach  equal  value 
on  cloudy  nights  the  net  loss  by  radiation  is  small.  Smoke  differs  from 
water  vapor  in  being  relatively  transparent  to  long  heat  waves.  There 
is  a  relatively  large  difference  in  the  way  violet  (or  blue)  and  yellow  (or 
red)  are  transmitted  through  dust  in  the  air^ — for  example,  the  sun  is 
yellow  or  red  at  horizon,  the  short  waves  not  being  transmitted  as  readily 
as  the  longer  yellow  and  red  waves.  The  sun  looks  red  through  smoke, 
showing  the  same  effect.  The  smoke  screen  appears  opaque  because  the 
eye  uses  the  shorter  waves  but  it  must  be  very  much  less  opaque  to  the 
long  waves  which  the  earth  radiates. 


PROTECTION  AGAINST  FROST  375 

Covering  and  Spraying. — The  protection  of  plants  from  frost  by- 
covering  tliem  with  paper  or  cloth  is  of  course  effected  through  saving 
of  the  heat  otherwise  lost  through  radiation.  The  efficacy  of  this 
method  is  well  known  though  it  is  not  practicable  in  the  orchard.  ^^^  An 
experiment  in  California  showed  that  with  an  outside  minimum  of  19° 
the  lowest  temperature  under  a  paper  covering  spread  over  an  almond 
tree  was  24°,  a  saving  equal  to  the  raise  in  temperature  secured  in  many 
instances  by  orchard  heating. 

The  protective  effects  of  water  spray  were  investigated  in  Utah  by 
keeping  a  block  of  apricots  under  a  continuous  fine  spray  during  a  frost. ^°^ 
Ice  formed  on  the  blossoms  and  it  finally  appeared  that  only  the  sprayed 
trees  were  damaged.  The  injury  was  not  a  mere  failure  to  set  fruit; 
there  was  actual  killing.  In  view  of  the  work  of  Harvey^''  it  seems  prob- 
able that  in  this  case  the  ice  formation  on  the  surfaces  of  the  blossoms 
inoculated  the  inside  tissues  with  ice  crystals  and  actually  hastened  their 
freezing. 

Orchard  Heating. — The  most  successful  results  so  far  achieved  in  pre- 
venting low  temperatures  have  been  realized  by  the  use  of  large  numbers 
of  small  heaters,  warming  the  air  itself.  This  practice  has  become  a 
settled  part  of  orchard  routine  in  some  sections;  in  others  it  has  been  in 
extensive  use  but  is  now  almost  obsolete.  There  can  be  no  doubt  of 
its  efficacy  in  some  cases.  Frequently,  however,  it  has  been  considered 
too  expensive  insurance.  The  heating  capacity  of  a  set  of  heaters  is 
limited  and  sometimes  in  a  severe  freeze  the  temperature  sinks  so  low 
they  are  unable  to  maintain  a  protecting  temperature,  or  in  some  cases 
a  high  cold  wind  renders  them  useless.  On  the  other  hand,  a  few  degrees 
of  freezing  rarely  destroys  a  whole  crop.  The  full  value  of  these  heaters 
is,  then,  realized  only  with  minima  in  a  certain  narrow  range;  with 
minima  outside,  they  are  either  unnecessary  or  useless. 

It  is  probable  that  failure  to  realize  these  limitations  led  to  the  instal- 
lation, during  the  greatest  vogue,  of  orchard  heating  equipment  in  many 
places  where  its  true  usefulness  is  rarely  available  and  that  failure  to 
realize  its  limitations  at  the  outset  caused  unjustifiable  expectations  of 
its  value.  In  either  case  the  reaction  was  bound  to  cloud  the  instances 
and  circumstances  in  which  it  can  be  of  real  worth. 

Furthermore,  orchard  heating  has  been  invoked  at  times  when  the 
difficulty,  supposedly  frost,  was  in  reality  something  entirely  different. 
At  one  time  many  cherry  growers  at  The  Dalles,  in  Oregon,  installed 
extensive  heating  equipment  to  induce  a  proper  setting  of  fruit  when 
their  orchards  were  of  self  sterile  and  inter-sterile  varieties  and  what 
they  actually  needed  was  provision  for  proper  cross  pollination.  Orchard 
heating  cannot  make  weak  trees  set  heavy  crops.  In  view  of  the  equal 
influence  of  freezing  on  blossoms  of  weak  and  of  strong  trees,  as  cited 
previously  in  this  section,  the  increases  sometimes  reported  in  fruit  set 


376  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

after  frost  on  nitrate-fertilized  trees  may  constitute  a  splendid  testimonial 
for  nitrate  fertilization  but  they  do  not  in  themselves  indicate  that 
orchard  heating  without  fertilization  would  have  been  beneficial. 

Heat  Units  in  the  Fuel. — Limits  must  be  recognized  to  the  amount  of 
actual  heating  any  ordinary  equipment  can  secure. 

McAdie^^^  indicates  this  in  some  interesting  calculations.  "At  the  present 
time,"  he  states,  "with  a  hundred  burners  to  the  acre,  using  a  gallon  each  of  oil, 
something  Hke  15,000,000  British  thermal  units  or  3,760,000  [kilogram]  calories 
would  be  given  off,  provided  the  combustion  was  perfect,  which  of  course  is  never 
true.  Now,  to  raise  the  temperature  of  the  air  1°F.  over  an  acre  to  a  height  of  15 
feet  is  practically  heating  653,400  cubic  feet  of  air.  In  practice  it  is  found  that  to 
maintain  the  temperature  on  a  still  night  1°  above  the  freezing  temperature 
requires  0.252  calories  per  hour  per  cubic  foot.  Therefore  for  a  period  of  7 
hours,  which  is  about  the  average  duration  of  a  low  temperature  [McAdie  wrote 
in  California],  although  10  hours  is  a  safer  period,  there  will  be  required  1,138,200 
calories.  And  if  a  raise  of  5°  is  required  it  is  evident  that  more  than  5,500,000 
calories  are  needed  or  more  than  the  full  number  of  heat  units  in  the  fuel  under 
perfect  combustion." 

In  practice  oil  is  burned  generally  at  a  faster  rate  than  that  used  in 
IVIcAdie's  calculations,  but  the  pubhshed  results  of  careful  experiments 
indicate  that  the  actual  heating  achieved  rarely  exceeds  5°  and  that  4° 
is  a  liberal  estimate  of  what  may  be  expected  with  ordinarily  favorable 
conditions.  A  breeze  of  6  miles  an  hour  materially  lowers  the  net  gain 
of  heat;  any  movement  lowers  it  somewhat  and  dead  calms  are  rare. 
According  to  Young,  in  the  lard-pail  type  of  heaters  only  about  40  per 
cent  of  the  heat  in  the  oil  is  actually-  realized  in  combustion  and  even 
in  the  high  stack  type  it  is  doubtful  if  more  than  70  or  80  per  cent  of 
its  fuel  value  is  attained.  A  still  further  loss  is  caused  by  the  height  of 
the  "ceiling  layer"  of  air  which,  though  variable,  permits  in  any  case 
the  accumulation  of  heat  at  a  height  above  the  trees. 

Height  of  the  ''Ceiling  Layer." — The  holding  of  heated  air  within  a 
few  feet  of  the  ground  appears  mysterious  unless  the  inversion  of  tem- 
perature be  considered.  Data  introduced  previously  have  shown  that 
the  normal  adiabatic  cooling  of  the  air  upward  from  the  earth,  charac- 
teristic of  daytime,  is  modified  during  radiation  nights  and  that  the  air 
only  a  few  feet  above  the  ground  is  distinctly  warmer  than  that  at  or 
near  the  surface.  It  is  this  layer  of  warm  air,  acting  as  a  roof  or  ceiling, 
that  makes  possible  the  warming  of  the  air  at  the  level  of  the  trees. 
As  the  warmed  air  ascends  from  the  heaters  it  mixes  with  other  some- 
what cooler  air  and  the  mixture  finally  reaches  a  layer  of  the  same  tem- 
perature; it  then  has  no  impulse  to  rise  further. 

Figure  38,  by  Humphreys,"  shows  a  typical  frosty  morning  tempera- 
ture gradient  and  is  used  by  him  to  indicate  how  heat  may  be  wasted. 
He  shows  that  under  the  given  conditions  any  portion  of  the  surface 


PROTECTION  AGAINST  FROST 


377 


air  warmed  from  32  to  34°F.  would  rise  to  about  30  feet  only,  as  shown 
by  the  adiabatic  curve  from  34°,  until  it  would  reach  the  layer  of  air 
having  a  temperature  equal  to  its  own.  If  it  were  warmed  to  40°, 
however,  it  must  rise  over  250  feet,  cooling  somewhat  by  diminished 
pressure,  until  it  reaches  air  with  an  equal  temperature.  Thus  in  one 
case  the  ceiling  is  about  30  feet  high,  in  the  other  it  is  250  feet  high.  When 
the  gradient  begins  at,  say,  24°  instead  of  32°,  in  other  words  when  the 


900 


.£  500 
c 
o 

P   400 


300 


200 


100 


\ 

\ 

\ 

\ 

\ 

7-> 

TEM 

'PICA 
°ERA1 

L    HO 
URE  1 

RNIh] 
NVER. 

G 
SION 

/ 

\ 

/ 

J 

k 

,«9 

,^ 

f 

■? 

k 

\ 
\ 

\ 

^ 

Mti^ 

% 

ZZ       33        34 


35 


36         2.T 


Temp  era+u  re,d  eg.fohr. 

Fig.  38. — Illustrating  the  physical  possibility  of  protecting  outdoors  from  frost  by  artificial 
heating.      (After  Humphreys^'') 


outside  unheated  surface  air  is  at  24°,  whether  or  not  the  gradient  is 
affected  at  500  feet,  the  ceiling  above  the  34°  mark  is  raised,  meaning 
that  not  only  must  the  air  now  be  heated  from  24  to  34°,  10  degrees 
instead  of  2,  but  a  greater  amount  of  air  must  be  heated.  The  increasing 
difficulty  of  heating  toward  morning  is  due  evidently  to  other  factors 
besides  the  heaters  themselves. 

If  a  few  large  fires  are  employed  the  body  of  warmed  air  rising  from 
them  is  so  great  that  it  does  not  become  mixed  readily  and  rises  farther 


378  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

than  the  heat  from  the  small  fires,  being  thus  rendered  ineffective  in 
warming  the  air  at  lower  levels.  Large  fires  of  course  emit  a  considerable 
amount  of  radiation  heat  which  warms  the  surfaces  exposed,  but  since 
the  intensity  of  heating  by  radiation  diminishes  as  the  square  of  the 
distance  from  the  source  of  heat  it  soon  becomes  ineffective.  In  addi- 
tion the  current  set  up  above  the  large  fire  draws  in  the  colder  surface 
air  to  replace  the  warmed  air  driven  high  aloft  and  it  is  easy  to  conceive 
that  it  may  disturb  ceiling  layers  considerably. 

Effect  of  Wind. — Winds,  besides  carrying  heat  away  directly,  break 
up  the  "ceiling  layer"  of  warm  air  and  unless  the  heated  areas  are  very 
large  and  the  wind  such  that  the  warmed  air  is  "blown  down,"  they 
make  heating  efforts  of  little  avail.  Windbreaks,  therefore,  though  at 
times  they  may  invite  frost  conditions,  may  render  heating  more  effec- 
tive, though  they  cannot  preserve  tjie  ceiling  layer  which  is  necessary 
for  full  realization  of  its  possibilities. 

Humphreys, ^^  assuming  a  radiation  per  minute  per  square  centimeter  of 
0.1  calorie  and  evidently  basing  his  calculations  on  soil  surface  area  alone, 
disregarding  vegetative  surfaces,  concluded  that  for  each  plot  of  ground  10 
meters  by  10  meters  there  would  be  needed  per  hour  6,000,000  calories,  which, 
assigning  a  value  of  8,500  calories  per  gram  of  petroleum,  indicates  the  need  of 
approximately  a  pint  and  a  half  of  oil  per  hour  to  offset  radiation  or  to  hold  the 
temperature  from  falling.  If  a  moderate  air  movement  occur,  new  air  must  be 
warmed  constantly.  Humphreys,  assuming  the  dewpoint  below  32°,  land  sur- 
face horizontal,  temperature  of  air  32°  and  a  wind  of  2K  miles  per  hour  (approxi- 
mately 1  meter  per  second),  with  air  weight  1,290  grams  per  cubic  meter,  makes 
an  interesting  calculation  of  the  amount  of  heat  necessarj'-  to  warm  the  entering 
air  2°C.  to  an  elevation  of  12  meters.  He  states:  "Now  the  specific  heat  of  the 
atmosphere  is  very  approximately  0.24.  Hence  to  warm  1  cubic  meter  of  the 
given  air  1°C.  requires  about  310  calories.  Hence,  to  warm  the  air  2°C.  to  an 
elevation  of  12  meters,  as  it  enters  the  given  area  with  the  given  velocity  of  1 
meter  per  second,  will  require,  per  linear  meter  at  right  angles  to  its  direction, 
approximately  2  X  12  X  310  X  7,440  calories  per  second,  or  the  consumption  of, 
roughly,  3.7  liters  or  6.5  pints  of  oil  per  hour." 

A  considerable  amount  of  the  heat  imparted  to  the  air  as  it  enters  is  retained 
while  the  air  drifts  through  the  orchard;  therefore,  though  radiation  must  be 
fought  equally  at  all  points  the  raising  of  air  temperature  itself  is  moit  jt^roperly 
done  on  the  windward  edge.  With  the  somewhat  idealized  conditions  enumer- 
ated above,  assuming  an  orchard  1  kilometer  square  (about  247  acres)  with  the 
breeze  at  right  angles  to  one  side  the  oil  requirements  are  stated  by  Humphreys : 
to  counteract  radiation  8,600  liters;  to  warm  the  entering  air  3,700  liters.  A  rec- 
tangular orchard  might  require  more  or  less  oil  to  warm  the  entering  air,  accord- 
ing to  the  direction  of  the  breeze  and  if  the  breeze  is  quartering  two  sides  must  be 
warmed,  but  the  amount  to  offset  radiation  alone  is  constant.  In  other  words 
the  oil  necessary  to  offset  radiation  is  determined  by  area  alone ;  the  amount  nec- 
essary to  warm  entering  air  is  determined  by  the  outline  of  the  orchard  and  by 
the  direction  and  velocity  of  the  wind. 


PROTECTION  AGAINST  FROST  379 

Concerning  the  influence  of  wind  velocity  Humphreys  says:  "Of  course  a 
greater  wind  velocity  than  2K  miles  per  hour,  the  velocity  above  assumed,  would 
appear  to  necessitate  a  correspondingly  larger  consumption  of  fuel  for  the  border 
or  entrance  heating.  But  this,  presumably,  is  not  true  in  practice,  since  probably 
even  this  velocity,  certainly  a  greater  one,  would  considerably  mix  the  surface- 
cooled  air  with  the  warmer  air  above,  and  thereby  decrease  the  amount  of 
necessary  heating.  During  a  perfect  calm  the  required  border  heating  is  zero; 
it  is  also  zero  when  there  is  a  fairly  good  breeze  and  hence  has  its  maximum  value 
at  some  quite  moderate  intermediate  velocity." 

It  should  be  noted  that  Humphreys  is  stating  that  the  higher  the 
velocity  of  the  air  movement  the  higher  the  air  temperature  is  likely  to  be. 
This  is  quite  different  from  the  case  of  high  wind  at  a  dangerous  tem- 
perature, for  here  the  heating  required  increases  with  the  wind  velocity 
and  too  many  times  becomes  impossible. 

The  choice  of  heater  types  depends  on  the  nature  of  the  service 
required.  In  some  sections  where  dangerous  temperatures  are  of 
short  duration  the  simple  1-gallon  heaters  will  be  adequate;  in  other 
sections  longer  burning  may  be  required.  Young- '^  points  out  that  the 
size  of  the  temperature  inversion  characteristic  of  many  of  the  California 
frosts  permits  the  use  of  stack  heaters  which,  perhaps,  could  not  be 
employed  in  sections  where  the  temperature  inversion  is  weaker.  No 
one  type  is  best  for  all  sections  or  for  all  occasions  in  one  section. 

Conditions  Determining  Practicability. — No  general  discussion  can 
decide  the  question  whether  orchard  heating  is  profitable.  The  con- 
tinuance of  the  practice  in  certain  sections  over  a  long  period  is  rather 
good  evidence  that  with  conditions  as  they  are  in  those  sections  it  is 
either  profitable  or  necessary  or  both.  The  necessity  of  the  practice, 
if  fruit  is  to  be  grown  in  a  certain  spot,  may  mean  that  it  is  desirable  or  it 
may  mean  that  the  spot  should  be  devoted  to  some  other  crop.  If  the 
value  per  acre  of  the  crop  is  high,  as  with  oranges,  heating  may  be 
economically  sound;  if  the  value  per  acre  of  the  crop  is  low,  heating  is 
of  doubtful  wisdom.  If  a  given  spot  is  exposed  to  several  frosts  a  year 
heating  is  likely  to  pay  as  compared  with  no  heating  but  it  may  be  that 
fruit  growing  should  be  abandoned  at  that  spot. 

The  installation  of  an  orchard  heating  equipment  involves  a  heavy 
overhead  expense.  Each  year  heaters  and  fuel  must  be  distributed  and 
made  ready.  The  chief  difference  in  expense  between  a  frosty  and  a 
frostless  spring  so  far  as  heating  is  concerned  is  in  the  oil  consumed  and  a 
reduction  or  increase  in  the  labor  charge.  The  profits  of  the  frostless 
season  are  taxed  only  somewhat  less  than  those  of  the  frosty  season. 
Frequently  the  yearlj^  expense  has  amounted  to  $20  per  acre;  it  has 
reached  $40.  In  many,  if  not  in  most,  fruit  growing  sections,  $40  per 
acre  added  to  the  initial  price  of  the  land  will  secure  sites  located  advan- 
tageously enough  to  escape  this  tax. 


380  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Orchard  heating  is  not  so  common  as  it  was  some  years  ago.  Certain 
sections  have  abandoned  it  altogether,  in  others  only  a  few  growers 
continue  it.  In  some  instances  too  much  has  been  expected  of  it;  in 
others  the  falling  in  fruit  prices  from  an  artificial  level  has  been  a  con- 
tributing cause,  but  probably  in  the  majority  of  cases  it  has  been  aban- 
doned for  the  excellent  reason  that  it  has  not  paid. 

It  will  be  seen  from  the  Wauseon  figures  that  heating  at  that  point 
would  be  an  expensive  insurance  considering  the  number  of  times  it 
would  be  useful.  If,  in  addition,  the  orchards  are,  as  is  the  case  fre- 
quently, bearing  chiefly  in  alternate  years,  the  likelihood  of  heating  being 
profitable  over  a  long  term  is  further  reduced.  Assuming  a  damaging 
frost  in  half  the  blossoming  seasons,  a  ratio  far  greater  than  that  for  the 
largest  apple  growing  sections,  and  assuming  a  crop  in  alternate  years, 
the  chance  of  heating  being  required  to  save  a  crop  is  3^^  X  M  or  1  in 
4.  If  damaging  frost  occurs  once  in  3  years  the  chance  is  3^^  X  li  or 
1  in  6.  At  Wauseon,  with  very  liberal  allowance,  it  is,  for  the  King 
apple,  2  in  15.  It  is  significant  that  much  of  the  experimental  work  on 
orchard  heating  has  been  done  at  temperatures  above  freezing  because 
there  was  not  enough  frosty  weather  for  all  the  tests.  There  are,  too, 
in  almost  all  sections,  springs  when  the  crop  is  damaged  by  high  cold 
winds,  under  such  conditions  that  heating  fails  to  protect  it  sufficiently. 
If  a  season  of  this  kind  is  added  to  seasons  when  heating  is  unnecessary 
the  number  of  years  when  it  really  pays  is  still  further  reduced. 

The  fruit  grower  is  forced,  sooner  or  later,  consciously  or  uncon- 
sciously, to  consider  the  economic  doctrine  of  marginal  utility.  This 
means,  as  applied  to  the  topic  under  discussion,  that  until  all  the  land 
otherwise  well  adapted  to  fruit  growing  and  free  from  frost  danger  in  a 
given  area  is  in  use  for  that  purpose  it  is  of  doubtful  expediency  to  attempt 
fruit  growing  on  land  that  will  require  heating.  It  means,  too,  that  in 
seasons  when  profits  in  general  run  low  they  are,  other  things  equal, 
wiped  out  first  on  the  land  that  requires  heating. 

In  addition  to  the  doctrine  of  marginal  utility  the  grower  should 
apply  to  his  analysis  the  law  of  the  minimum.  Orchard  heating  is 
not  hkely  to  be  profitable  to  him  if  his  spraying  is  defective,  his  pruning 
poorly  done,  his  land  lacking  in  drainage  or  irrigation,  his  trees  weak  or 
if  his  fruit  is  not  marketed  to  advantage.  "When  he  is  satisfied  that  he  has 
developed  these  essentials  so  that  none  of  them  is  hmiting  his  profits  and 
that  frost  is  the  limiting  factor  he  can  consider  orchard  heating.  In  some 
cases  it  will  be  profitable;  in  more  cases  it  will  not. 

FROST  EFFECTS 
Manifestations  of  frost  injury  aside  from  the  dropping  of  the  fruit 
are  sometimes  found.     The  so-called  bull-necked  pears  previously  men- 
tioned are  rather  common  and  are  sometimes  confused  with  seedless 


PROTECTION  AGAINST  FROST  381 

fruit,  particularly  with  that  arising  from  late  bloom.  Russet  bands, 
generally  extending  more  or  less  completely  around  the  middle  of  the 
fruit,  though  sometimes  near  the  calyx  end,  occur  on  pears  and  occasion- 
ally on  apples.  Similar  russeted  areas,  frequently  somewhat  raised,  but 
less  regular  in  location,  are  found  on  plums.  Apples  and  pears  with  this 
form  of  injury  are  said  to  wilt  rather  rapidly.^"*"* 

In  the  apple  the  outside  leaves  of  a  cluster  sometimes  show  a  form 
of  injury  called  "frost-blister."^'*^  As  observed  in  New  Hampshire  and 
Missouri,  this  injury  does  not  appear  to  reduce  the  size  of  the  affected 
leaves  which  are  normally  small  and  it  apparently  does  not  extend  beyond 
the  first  two  or  three  leaves  to  unfold.  The  injury  evidently  may  occur 
when  the  buds  are  still  verj^  little  advanced.  The  appearance  is  suffi- 
ciently described  by  the  name;  the  "blisters"  are  caused  by  the  separa- 
tion of  the  upper  and  the  lower  surfaces.  The  leaves  tend  to  curl  and 
in  many  cases  drop  off.  Inasmuch  as  those  most  affected  are  of  doubtful 
importance  to  the  growing  spur  this  type  of  injury  is  probably 
unimportant. 

Another  interesting  consequence  of  frost  injury  is  the  so-called 
"secondary  bloom."  When  there  is  extensive  killing  of  fruit  buds  the 
spurs  which  have  bloomed  may  form  new  blossoms,  which  in  some  cases 
have  been  observed  to  mature  fruit,  sometimes  with  and  sometimes 
without  seeds.  The  same  phenomenon  may  occur  independently  of  any 
frost.     It  is  discussed  more  fully  under  Fruiting  Habit. 

Summary. — The  critical  temperature  for  opening  flower  buds  varies 
greatly  with  their  stage  of  development  and  somewhat  with  species  and 
variety.  Some  of  the  fully  expanded  flowers  of  many  fruit  varieties 
will  withstand  an  apparent  temperature  of  25°F.  without  injury,  though 
some  will  be  killed  at  or  above  this  point.  Unopened  flower  buds  are 
considerably  more  frost  resistant.  Plants  in  a  vigorous  condition  are 
apparently  no  more  resistant  to  frost,  but  they  possess  greater  recupera- 
tive ability.  Often  trees  losing  a  considerable  percentage  of  their  blos- 
soms from  frost  still  have  enough  good  buds  to  bear  a  full  crop.  In 
many  cases  danger  from  frost  can  be  avoided  to  a  great  extent  by  the 
selection  of  late  blossoming  varieties.  Relatively  greater  immunity  from 
frost  danger  can  be  secured  in  this  way  with  those  fruits  and  in  those 
sections  showing  a  considerable  range  in  blossoming.  The  blossom- 
ing season  of  many  fruits  may  be  slightly  retarded  by  certain  cultural 
practices,  but,  except  in  the  case  of  fruits  like  the  strawberry  that  can 
be  entirely  covered,  such  methods  of  frost  protection  are  of  secondary 
importance.  In  new  sections  the  probable  blossoming  dates  of  certain 
varieties  of  fruit  may  be  foretold  with  considerable  accuracy  by  com- 
parison with  the  blossoming  season  of  native  plants.  The  probability 
of  frost  occurring  on  any  particular  night  can  be  foretold  fairly  accurately 
by  the  middle  of  the  preceding  afternoon.     Several  methods  are  employed, 


382  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

some  of  them  being  more  reliable  in  certain  districts  than  others.  The  pre- 
dictions for  regular  Weather  Bureau  "key"  stations,  corrected  to  apply  to 
local  conditions  are  of  greatest  general  use.  Several  distinct  methods  of 
preventing  frost  have  been  used  in  fruit  growing  sections.  The  use  of 
smoke  screens  is  of  little  value  in  checking  the  radiation  of  heat  at  night. 
Orchard  heating  is  practicable  under  certain  conditions.  However,  only  a 
limited  protection  is  afforded  by  orchard  heaters,  the  exact  amount  de- 
pending on  the  height  of  the  "ceiling  layer"  of  the  air,  on  the  number  and 
kind  of  heaters  and  on  the  amount  of  wind.  A  protection  of  4  or  5°F.  on 
typical  frosty  nights  is  all  that  can  be  expected  under  average  conditions. 
Before  the  installation  of  orchard  heating  equipment  is  warranted  there 
should  be  reasonable  assurance  that  growing  conditions  during  the  average 
season  and  the  average  margin  of  profit  warrant  it.  Frost  occurring 
after  the  time  of  fruit  setting  may  occasionally  arrest  the  further  develop- 
ment of  seeds  and  still  permit  the  fleshy  tissues  to  develop  and  mature, 
giving  rise  to  fruits  abnormal  in  size  and  shape.  It  may  also  cause  the 
appearance  of  "frost  rings"  or  bands  of  russet  around  the  apical  end  of 
the  fruit.  It  occasionally  leads  to  certain  other  pathological  conditions 
in  fruit  or  foliage. 

Suggested  Collateral  Reading 

Schimper,    A.   F.   W.     Plant   Geography  upon   a   Physiological   Basis.     Pp.   35-51; 

241-259.     Oxford,  1903. 
Chandler,  W.  H.     Hardiness  of  Peach  Buds,  Blossoms  and  Young  Fruit  as  Influenced 

by  the  Care  of  the  Orchard.     Mo.  Agr.  Exp.  Sta.  Cir.  31.     1908. 
Emerson,  R.  A.     Cover  Crops  for  Young  Orchards.     Nebr.  Agr.  Exp.  Sta.  Bui.  92. 

1903. 
Gladwin,  F.  E.     Winter  Injury  in  Grapes.     N.  Y.  Agr.  Exp.  Sta.  Bui.  433.     1917. 
Harvey,  R.  B.     Hardening  Processes  in  Plants.     Jour.  Agr.  Res.  15:  2,  1918. 
Hooker,  H.  D.,  Jr.     Pentosan  Content  in  Relation  to  Winter  Hardiness.     Proc.  Am. 

See.  Hort.  Sci.     17:  204-207.     1920. 
Macoun,  W.  T.     Overcoming  Winter  Injury.     Proc.  Am.  Soc.  Hort.  Sci.     Pp.  15-27. 

1908-9. 
Rosa,  J.  T.,  Jr.     The  Hardening  Process  in  Vegetable  Plants.     Mo.  Agr.  Exp.  Sta. 

Research  Bui.  48.     1921. 
Selby,  A.  D.     Fall  and  Early  Winter  Injuries  to  Orchard  Trees  and  Shrubbery  by 

Freezing.     Ohio  Agr.  Exp.  Sta.  Bui.  192.     1908. 
Waite,  M.  B.     Fruit  Trees  Frozen  in  1904.     U.  S.  D.  A.,     Bur.  PI.  Ind.  Bui.  51  (part 

3).     1905. 
Wiegand,  K.  M.     The  Biology  of  Twigs  in  Winter.     Bot.  Gaz.     41:  373.     1906. 

Literature  Cited 

1.  Abbe,  C.     U.  S.  D.  A.,  Weather  Bur.  No.  342:  168.     1905. 

2.  Alter,  J.  C.     U.  S.  D.  A.,  Mo.  Weather  Rev.     40:  929.     1912. 

3.  Alwood,  W.  B.     Va.  Agr.  Exp.  Sta.  Bui.  147.     1903. 

4.  Anthony,  R.  D.     N.  Y.  Agr.  Exp.  Sta.  Bui.  432.     1917. 

5.  Augur,  P.  M.     Proc.  Am.  Pom.  Soc.     P.  54.     1885. 

6.  Baake,  A.  L.     Proc.  Am.  Soc.  Hort.  Sci.     17:  279.     1920. 


TEMPERATURE  RELATIONS  383 

7.  Bailey,  L.  H.     Mich.  Agr.  Exp.  Sta.  Bui.  40.     1888. 

8.  Bailey,  L.  H.     Cornell  Univ.  Agr.  Exp.  Sta.  Bui.  117.     1896. 

9.  Bailey,  L.  H.     Survival  of  the  Unlike.     P.  297.     New  York,  1901. 

10.  Bailey,  L.  H.  The  Principles  of  Fruit  Growing.     P.  11.     New  York,  1906. 

11.  Ballantyne,  A.  B.     Utah  Agr.  Exp.  Sta.  Bui.  128.     1913. 

12.  Balmer,  J.  A.     Wash.  Agr.  Exp.  Sta.  Bui.  30.     1897. 

13.  Baragiola,  W.  I.  and  Godet,  C.     Landw.  Jahrb.     48:  275.     1914. 

14.  Bartlett,  G.     Horticulturist.     1:549.     1847. 

15.  Bates,  C.  G.     U.  S.  D.  A.,  Forest  Service  Bui.  86.     1911. 

16.  Beach,  S.  A.,  and  Allen,  F.  W.,  Jr.     la.  Agr.  Exp.  Sta.  Res.  Bui.  21.     1915. 

17.  Beach,  S.  A.,  and  Close,  C.  P.     N.  Y.  Agr.  Exp.  Sta.  Ann.  Kept.     15:  408. 

1897. 

18.  Bedford  H.  A.  R.  and  Pickering,  S.  U.     2d  Rept.  Woburn  Exp.  Fruit  Farm. 

P.  242.  London,  1900. 

19.  Bigelow,  F.  H.     U.  S.  D.  A.,  Weather  Bur.  Bui.  R.     1908. 

20.  Blodgett,  L.     Climatology  of  the  U.  S.     P.  437.     1857. 

21.  Bonebright,  J.  E.     Ida.  Agr.  Exp.  Sta.  Bui.  35.     1903. 

22.  Boussingault,  J.  B.     Rural  Economy.     Transl.  by  Law.     P.  255.     New  York, 

1855. 

23.  Bouyoucos,  G.  J.     Mich.  Agr.  Exp.  Sta.  Tech.  Bui.  26.     1916. 

24.  Bouyoucos,  G.  J.     Mich.  Agr.  Exp.  Sta.  Tech.  Bui.  36.     1917. 

25.  Bouyoucos,  G.  J.     J.  Agr.  Res.     20:  267.     1920. 

26.  Bradford,  F.  C.     Thesis  Univ.     Maine.     1911. 

27.  Budd,  J.  L.     la.  Agr.  Exp.  Sta.  Bui.  7.     1889. 

28.  Budd,  J.  L.     la.  Agr.  Exp.  Sta.  Bui.  13.     1891. 

29.  Buffum,  B.  C.     Wyo.  Agr.  Exp.  Sta.  Bui.  34.     1896. 

30.  Cannon,  W.  A.     Plant  World.     20:  361.     1917. 

31.  Card,  F.  W.     Nebr.  Agr.  Exp.  Sta.  Bui.  48.     1897. 

32.  Card,  F.  W.     Bush  Fruits.     P.  24.     New  York,  1917. 

33.  Ibid.     P.  37. 

34.  Carpenter,  L.  G.     Col.  Agr.  Exp.  Sta.  Ann.  Rept.     3:  147.     1890;  4:  75.     1891. 

35.  Carrick,  D.  B.     Cornell  Univ.  Agr.  Exp.  Sta.  Mem.  36.     1920. 

36.  Chandler,  W.  H.     Mo.  Agr.  Exp.  Sta.  Bui.  74.     1907. 

37.  Chandler,  W.  H.     Mo.  Agr.  Exp.  Sta.  Cir.  31.     1908. 

38.  Chandler,  W.  H.     Mo.  Agr.  Exp.  Sta.  Res.  Bui.  8.     1913. 

39.  Chandler,  W.  H.     Proc.  Am.  Soc.  Hort.  Sci.     12:  118.     1915. 

40.  Chandler,  W.  H.     Correspondence,  1921. 

41.  Chapman,  H.  H.     Minn.  Agr.  Exp.  Sta.  Bui.  81.     1903. 

42.  Church,  J.  L.,  Jr.,  and  Ferguson,  S.  P.     Nev.  Agr.  Exp.  Sta.  Bui.  79.     1912. 

43.  Coit,  J.  E.     Ariz.  Agr.  Exp.  Sta.  Bui.  61.     1909. 

44.  Conley,  J.  D.,  and  Ridgaway,  C.  B.     Wyo.  Agr.  Exp.  Sta.   Bui.  23.     1896. 

Met.  Repts.     1898,  1899. 

45.  Coulter,  J.  M.,  Barnes,  C.  R.,  and  Cowles,  H.  C.     Textbook  of  Botany.     2:  585. 

New  York.     1911. 

46.  Cox,  H.  J.     U.  S.  D.  A.,  Weather  Bur.  Bui.  T.     1910. 

47.  Cox,  H.  J.     U.  S.  D.  A.,  Weather  Bur.  No.  583:177.     1916. 

48.  Craig,  J.     Cent.  (Can.)  Exp.  Farms  Bui.  22.     1895. 

49.  Craig,  J.     Cent.  (Can.)  Exp.  Farms  .\nn.  Rept.     10:  119.     1896. 

50.  Ibid.     10:  147.     1896. 

51.  Craig,  J.     la.  Agr.  Exp.  Sta.  Bui.  44.     1900. 

52.  Crandall,  C.  S.     Col.  Agr.  Exp.  Sta.  Bui.  41.     1898. 

53.  DeCandolle,  A.     Geog.  bot.  raison.     Paris,  1855. 

54.  Downing,  A.  J.     Horticulturist.     1 :  58.     1846. 


384  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

55.  Ibid.     2:  339.     1847. 

56.  Ibid.     2:416.     1847.. 

57.  Duchartre,  P.     Compt.  rend.     60:  754.     1865. 

58.  Emerson,  R.  A.     Nebr.  Agr.  Exp.  Sta.  Bui.  79.     1903. 

59.  Emerson,  R.  A.     Nebr.  Agr.  Exp.  Sta.  Bui.  92.     1906. 

60.  Emerson,  R.  A.     Nebr.  Agr.  Exp.  Sta.  Ann.  Rept.     19:  101.     1906. 

61.  Emerson,  R.  A.     Correspondence,  Dec.  14,  1920. 

62.  Emery,  S.  M.     Mont.  Agr.  Exp.  Sta.  Bui.  16.     1898. 

63.  Emery,  S.  M.     Mont.  Agr.  Exp.  Sta.  Bui.  24.     1899. 

64.  Eustace,  H.  J.     N.  Y.  Agr.  Exp.  Sta.  Bui.  269.     1905. 

65.  Fernow,  B.  E.     U.S.D.A.,  Forestry  Div.  Bui.  7.     1893. 

66.  Finch,  V.  C,  and  Baker,  D.  O.     Geography  of  the  World's  Agriculture.     P.  77. 

Washington,  1917. 

67.  Fisher,  W.  R.     Schlich's  Manual  of  Forestry.     4:  505.     1907. 

68.  Ibid.     4:  522. 

69.  Frank,  A.  B.     Die  Krankheiten  der  Pflanzen.     2:  204.     Breslau,  1895. 

70.  Friedrich,  J.     Ueber  den  Einfluss  der  Witterung  auf  den  Baumwachs.     P.  155. 

Vienna,  1897. 

71.  Garcia,  F.,  and  Rigney,  J.  W.     N:  Mex.  Agr.  Exp.  Sta.  Bui.  89.     1914. 

72.  Ibid.     Bui.  100.     1916. 

73.  Gladwin,  F.  E.     N.  Y.  Agr.  Exp.  Sta.  Bui.  433.     1917. 

74.  Goff,  E.  S.     Wis.  Agr.  Exp.  Sta.  Ann.  Rept.     15:  220.     1898. 

75.  Ibid.     16:  283.     1899. 

76.  Goff,  E.  S.     Wis.  Agr.  Exp.  Sta.  Bui.  77.     1899. 

77.  Gould,  H.  P.     Peach  Growing.     P.  354.     New  York,  1918. 

78.  Gourley,  J.  H.     N.  H.  Agr.  Exp.  Sta.  Tech.  Bui.  12.     1917. 

79.  Greene,  L.     Purdue  Univ.  Agr.  Exp.  Sta.  Ann.  Rept.     31:  46.     1918. 

80.  Green,  S.  B.     Minn.  Agr.  Exp.  Sta.  Bui.  32.     1893. 

81.  Green,  W.  J.,  and  Ballou,  F.  H.     Ohio  Agr.  Exp.  Sta.  Bui.  157.     1904. 

82.  Grossenbacher,  J.  G.     N.  Y.  Agr.  Exp.  Sta.  Tech.  Bui.  23.     1912. 

83.  Gunderson,  A.  J.     111.  Agr.  Exp.  Sta.  Bui.  218.     1919. 

84.  Hammon,  W.  H.     Cited  by  71. 

85.  Hansen,  N.  E.     S.  D.  Agr.  Exp.  Sta.  Bui.  50.     1897. 

86.  Ibid.     Bui.  65.     1899. 

87.  Harvey,  R.  B.     J.  Agr.  Res.     15:  2.     1918. 

88.  Hedrick,  U.  P.,  Booth,  N.  O.,  and  Taylor,  O.  M.     N.  Y.  Agr.  Exp.  Sta.  Bui.  275. 

1906. 

89.  Hedrick,  U.  P.     Hort.  Soc.  of  N.  Y.  Mem.     2:  119.     1907. 

90.  Hedrick,  U.  P.     N.  Y.  Agr.  Exp.  Sta.  Bui.  299.     1908. 

91.  Hedrick,  U.  P.     Plums  of  New  York.     P.  103.     Albany,  1911. 

92.  Hedrick,  U.  P.     N.  Y.  Agr.  Exp.  Sta.  Bui.  355.     1912. 

93.  Herrick,  R.  S.,  and  Bennett,  E.  R.     Col.  Agr.  Exp.  Sta.  Bui.  171.     1910. 

94.  Hooker,  H.  D.,  Jr.     Proc.  Am.  Soc.  Hort.  Sci.     17:  204-207.     1920. 

95.  Hopkins,  A.  D.     U.S.D.A.,  Mo.  Weather  Rev.  Sup.  9.     1918. 

96.  Howard,  A.,  and  Howard,  G.  L.  C.     Sci.  Rept.  Agr.  Inst.  Pusa.  48.     1916-1917. 

97.  Humphreys,  W.  J.     U.S.D.A,  Mo.  Weather  Rev.     42:  562.     1914. 

98.  Jehle,  R.  A.     Cornell  Univ.  Agr.  Exp.  Sta.  Cir.  26.     1914. 

99.  Johnston,  E.  S.     Am.  J.  Bot.     6:  373-379.     1919. 

100.  Jones,  C.  H.,     Edson,  A.  W.,  and  Morse,  W.  J.     Vt.  Agr.  Exp.  Sta.  Bui.  103. 

1903. 

101.  Kimball,  H.  K.,  and  Young,   F.  D.     U.S.D.A.,   Mo.  Weather  Rev.     48:  461. 

1920. 

102.  King,  F.  H.     Wis.  Agr.  Exp.  Sta.  Ann.  Rept.     13:  207.     1896. 


TEMPERATURE   RELATIONS  385 

103.  Lazenby,  W.  R.     Proc.  Am.  Pom.  Soc.     P.  54.     1885. 

104.  Lindley,  J.     The  Theory  and  Practice  of  Horticulture.     P.  150.     London,  1855. 

105.  Ibid.     P.  155. 

106.  Linsser,  C.     Cited  by  Bailey,  L.  H.     Survival  of  the  Unlike.     P.  292.     New 

York,  1901. 

107.  Lippincott,  J.  B.     U.S.D.A.,  Ann.  Rept.     P.  200.     1862. 

108.  Livingston,  B.  E.     Physiol.  Res.     1:8.     1916. 

109.  Livingston,  B.  E.,  and  Livingston,  G.  J.     Bot.  Gaz.     56:  5.     1913. 

110.  Lloyd,  F.  E.     Plant  World.     20:  121.     1917. 

111.  Loomis,  E.     Treatise  on  Meteorology.     P.  91.     New  York,  1892. 

112.  Ibid.      P.  93. 

113.  MacDougal,  D.  T.     Hydration  and  Growth,     ('arn.   Inst.   Wash.   Publ.  297. 

P.  167.      1920. 

114.  Macoun,  W.  T.     Rept.  Cent.  (Can.)  Exp.  Farms.     12:  99.     1899. 

115.  Ibid.      13:  73.     1900. 

116.  Ibid.      13:  92.     1900. 

117.  Macoun,  W.  T.     Cent.  (Can.)  Exp.  Farms  Bui.  38.     1901. 

118.  Macoun,  W.  T.     Proc.  Am.  Soc.  Hort.  Sci.     3:  7.     1906. 

119.  Macoun,  W.  T.     Cent.  (Can.)  Exp.  Farms  Bui.  38.     2d  ed.     1907. 

120.  Macoun,  W.  T.     Proc.  Am.  Soc.  Hort.  Sci.     6:  15.     1909. 

121.  Macoun,  W.  T.     Trans.  Mass.  Hort.  Soc.  Pt.  1.     P.  39.     1916. 

122.  Marvin,  C.  F.     U.S.D.A.,  Mo.  Weather  Rev.     42:  583.     1914. 

123.  Mason,  S.  C.     U.S.D.A.,  Bur.  PI.  Ind.  Bui.  192.     1911. 

124.  Maynard,  S.  T.     Agriculture  of  Massachusetts.     P.  348.     Boston,  1884. 

125.  Maynard,  S.  T.     Mass.  Agr.  Exp.  Sta.  Buls.  10.     1890;  15.     1891;  21.     1893. 

126.  McAdie,  G.     U.S.D.A,  Mo.  Weather  Rev.     40:  282.     1912. 

127.  Ibid.      40:  618. 

128.  McCall,  F.  E.     Amer.  Fruit  Grower.     39:  7.     July,  1920. 

129.  McLean,  F.  T.     Physiol.  Res.     2:  129.     1917. 

130.  Mell,  P.  H.     Ala.  Agr.  Exp.  Sta.  Bui.  8.     1890. 

131.  Mer,  E.     Compt.  rend.      114:242.     1892. 

132.  Ibid.      124:  nil.      1897. 

133.  Mikesell,  T.     U.S.D.A.,  Mo.  Weather  Rev.  Sup.  2.     1915. 

134.  Milham,  W.  I.     U.S.D.A.,  Mo.  Weather  Rev.     36:  250.     1908. 

135.  MLx,  A.  J.      Cornell  Univ.  Agr.  Exp.  Sta.  Bui.  382.     1916. 

136.  Moore,  W.  L.     Descriptive  Meteorology.     P.  82.     New  York,  1911. 

137.  Mosier,  J.  G.      111.  Agr.  Exp.  Sta.  Bui.  208.     1918. 

138.  MuUer-Thurgau,  H.     Landw.  Jahrb.     45:  453.     1886. 

139.  Munson,  W.  M.     Me.  Agr.  Exp.  Sta.  Ann.  Rept.     7:  96.     1893. 

140.  N.  Y.  Agr.  Exp.  Sta.  Ann.  Rept.      37:  468.     1919. 

141.  O'Gara,  P.  J.     U.S.D.A.,  Farmers'  Bui.  401.     1910. 

142.  Oskamp,  J.     Proc.  Am.  Soc.  Hort.  Sci.     14:  118.     1917. 

143.  Paddock,  W.,  and  Whipple,  O.  B.     Fruit  Growing  in  Arid  Regions.     P.  325. 

New  York,  1911. 

144.  Ibid.     P.  326. 

145.  Ibid.     P.  327. 

146.  Ibid.     P.  353. 

147.  Pantanelli,  E.     Atti.  accad.  Lincei.     27(1):  126-130;  148-153.     1918. 

148.  Pa.  Agr.  Exp.  Sta.  Ann.  Repts.     1892,  1893,  1894,  1895,  1896. 

149.  Petit,  A.     Rev.  hort.  13(N.S.):  206.     1913. 

150.  Pfeffer,  W.     Physiology  of  Plants.  Transl.  by  Ewart.     2:  236.     Oxford,  1903. 

151.  Ibid.     2:  237. 

152.  Ibid.     2:  246. 

25 


386  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

153.  Philips,  H.  A.     Thesis.  Cornell  Univ.     1920. 

154.  Porter,  E.  D.     Minn.  Agr.  Exp.  Sta.  Bui.  7.     1889. 

155.  Price,   H.  L.     Va.  Agr.  Exp.  Sta.  Ann.  Rept.     P.  206.     1909-1910. 

156.  Prillieux,  E.     Compt.  rend.      74:  1344.     1872. 

157.  Quaintance,  A.  L.     Ga.  Agr.  Exp.  Sta.  Ann.  Rept.     11:  123.     1899. 

158.  Ragan,  W.  H.     U.S.D.A.,  Div.  Pom.  Bui.  8.     1899. 

159.  Reed,  W.  G.     Proc.  2d  Pan-Amer.  Sci.  Cong.     P.  625.     1917. 

160.  Reed,    W.    G.,    and   ToUey,    H.    R.     U.S.D.A.,    Mo.    Weather    Rev.     44:  354. 

1916. 

161.  Roberts,  R.  H.     Proc.  Am.  Soc.  Hort.  Sci.     14:  105.     1917. 

162.  Rosa,  J.  T.  Jr.     Proc.  Am.  Soc.  Hort.  Sci.     16:  190.     1919. 

163.  Ibid.      17:  207-210.     1920. 

164.  Rosa,  J.  T.  Jr.     Mo.  Agr.  Exp.  Sta.  Res.  Bui.  48.     1921. 

165.  Sandsten,  E.  P.     Wis.  Agr.  Exp.  Sta.  Ann.  Rept.     21:258.     1904. 

166.  Sandsten,  E.  P.     Wis.  Agr.  Exp.  Sta.  Bui.  137.     1906. 

167.  Sandsten,  E.  P.     Wis.  Agr.  Exp.  Sta.  Res.  Bui.  4.     1910. 

168.  Schimper,   A.   F.   W.     Plant  Geography  upon  a  Physiological  Basis.     P.  34. 

Oxford,  1903. 

169.  Ibid.     P.  37. 

170.  Ibid.     P.  45. 

171.  Ibid.     P.  47. 

172.  Schneider,  Numa.  Rev.  hort.     11(N.S.):  21.     1911. 

173.  Schubler,  G.     Poggendorf's  Annal.  Phys.  u.  Chem.     10:  581.     1827. 

174.  Schuster,  C.  E.     Ore.  Agr.  Exp.  Sta.  Bien.  Crop  Pest  and  Hort.  Rept.     3:  44. 

1920. 

175.  Seeley,  D.  A.     U.S.D.A.,  Mo.  Weather  Rev.     36:  259.     1908. 

176.  Ibid.     45:  354.     1917. 

177.  Selby,  A.  D.     Ohio  Agr.  Exp.  Sta.  Bui.  192.     1908. 

178.  Selvig,  C.  G.     Rept.  Exp.  Farm,  Crookston,  Minn.     1917-18. 

179.  Shaw,  J.  K.     Mass.  Agr.  Exp.  Sta.  Ann.  Rept.     23:  177.     1911. 

180.  Shutt,  F.  T.     Trans.  Roy.  Soc.  Can.      (Ser.  2.)     9(4):  149.     1903. 

181.  Smith,  A.  M.     Ann.  Roy.  Bot.  Gar.  Peradeniya.     (Abs.  in  Bot.  Gaz.     44:  6. 

1917.) 

182.  Smith,  J.  W.     U.S.D.A,  Mo.  Weather  Rev.  Sup.  16.     1920. 

183.  Sorauer,   P.     Schutz   der  Obstbatime  gegen   Krankheiten.     P.   42.     Stuttgart, 

1900. 

184.  Ibid.     P.  46. 

185.  Squires,  R.  W.     Minn.  Bot.  Studies.     1 :  452.     1894-8. 

186.  Stevens,  N.  E.     Am.  J.  Bot.     4:  1.     1917. 

187.  Ibid.     4:  112. 

188.  Stockman,  W.  B.     U.S.D.A.,  Mo.  Weather  Rev.     32:  125.     1904. 

189.  Strausbaugh,  P.  D.     Bot.  Gaz.     71:  337.      1921. 

190.  Swezey,  G.  D.     Nebr.  Agr.  Exp.  Sta.  Ann.  Rept.     16:  95.     1903. 

191.  Swingle,  W.  T.     U.S.D.A.,  Bur.  PL  Ind.  Bui.  53.     1904. 

192.  Taft,  L.  R.      Mich.  Agr.  Exp.  Sta.  Sp.  Bui.  11.     1898. 

193.  Ibid.     Sp.  Bui.  40.     1907. 

194.  Ibid.     Sp.  Bui.  46.      1908. 

195.  Taft,  L.  R.,  and  Lyon,  T.  T.     Mich.  Agr.  Exp.  Sta.  Bui.  169.     1899. 

196.  Tufts,  W.  P.     Correspondence,  1921. 

197.  Von  Mohl,  C.     Bot.  Ztg.     6:  6.     1848 

198.  Waite,  M.  B.     U.S.D.A.,  Bur.  PI.  Ind.  Bui.  51.     1905. 

199.  Waldron,  C.  B.     N.  D.  Agr.  Exp.  Sta.  Bui.  25.     1896. 

200.  Ibid.  Bui.  49.     1901. 


TEMPERATURE  RELATIONS  387 

201.  Ward,  H.  W.     The  Book  of  the  Peach.     P.  27.     London,  1903. 

202.  Waugh,  F.  A.     Vt.  Agr.  Exp.  Sta.  Bui.  62.     1898. 

203.  Waugh,  F.  A.     Vt.  Agr.  Exp.  Sta.  Ann.  Kept.     11:270.     1898. 

204.  Ibid.     11:  273. 

205.  Waugh,  F.  A.     Vt.  Agr.  Exp.  Sta.  Bui.  74.     1899. 

206.  Webber,  H.  J.  et  al.     Cal.  Agr.  Exp.  Sta.  Bui.  304.     1919. 

207.  West,  F.  L.,  and  Edlefsen,  N.  E.     Utah  Agr.  Exp.  Sta.  Bui.  151.     1917. 

208.  West,  F.  L.,  and  Edlefsen,  N.  E.     J.  Agr.  Res.     20:  8.     1921. 

209.  Whipple,  O.  B.     Mont.  Agr.  Exp.  Sta.  Bui.  91.     1912. 

210.  Whitten,  J.  C.     Mo.  Agr.  Exp.  Sta.  Bui.  38.     1897 

211.  Ibid.     Bui.  49.     1900. 

212.  Whitten,  J.  C.     Mo.  Agr.  Exp.  Sta.  Res.  Bui.  33.     1919. 

213.  Wiegand,  K.  M.     Bot.  Gaz.     41:373.     1906. 

214.  Wiegand,  K.  M.     Plant  World.     9:  2.     1906. 

215.  Wilcox,  E.  V.     Mont.  Agr.  Exp.  Sta.  Bui.  22.     1899. 

216.  Wilson,  W.  M.     Standard  Cyclopedia  of  Horticulture.     3:  1282.     1915. 

217.  Winkler,  H.     Jahrb.  f.  Wiss.  Bot.     52:  467.     1913. 

218.  Young,  F.  D.     U.S.D.A.,  Farmers'  Bui.  1096.     1920. 

219.  Young,  F.  D.     U.S.D.A.,  Mo.  Weather  Rev.     48:  463.     1920. 


SECTION  IV 
PRUNING 

Fruit  production  by  the  trees,  shrubs  and  vines  that  yield  edible 
fruits  is  dependent  on  (1)  the  possession  of  the  mechanism  or  machinery 
for  fruit  production  that  is  characteristic  of  the  species  or  variety  in 
question  and  (2)  its  proper  and  more  or  less  efficient  functioning.  Thus 
it  is  characteristic  of  most  varieties  of  the  brambles  to  bear  fruit  clusters 
terminally  on  short  shoots  developing  from  lateral  buds  on  year-old 
canes.  If  the  plant  is  so  handled  as  to  prevent  or  reduce  the  formation 
of  lateral  shoots  of  this  type,  fruiting  is  correspondingly  limited.  It  is 
characteristic  of  certain  varieties  of  the  walnut  to  bear  terminally  only 
on  short  shoots  developing  from  terminal  buds  on  the  growth  of  the  previ- 
ous season.  Obviously  then  the  production  and  preservation  of  terminal 
buds  is  a  prerequisite  to  fruit  production  in  those  varieties.  The  peach 
bears  fruit  on  shoots  of  the  past  season  but  only  at  nodes  from  which  no 
lateral  branches  arise. 

However,  some  of  the  lateral  buds  on  last  year's  raspberry  and  black- 
berry canes  do  not  produce  fruiting  shoots;  some  of  the  shoots  from  ter- 
minal buds  of  the  walnut  are  barren  and  many  nodes  on  the  unbranched 
primary  peach  shoot  do  not  have  fruit  buds.  The  framework,  the 
machinery,  for  fruit  bud  formation  is  apparently  there,  but  no  fruit  buds 
are  formed.  The  mechanism  does  not  function  in  the  way  it  is  desired. 
This  functioning  or  non-functioning  of  the  fruiting  machinery  is  to  be 
regarded  as  a  definite  response  to  varying  conditions  within  the  tree — 
primarily  conditions  of  nutrition,  which  in  turn  may  be  influenced  by 
age,  vigor,  food  supply,  temperature,  humidity  and  many  other  factors. 

In  some  cases  production  is  limited  by  the  amount  of  fruiting  machin- 
ery, or,  as  the  grower  would  say,  the  amount  of  bearing  surface.  In 
others  the  limiting  factor  to  production  is  the  irregular,  imperfect  or 
inefficient  functioning  of  the  fruiting  mechanism.  For  the  grower  the 
ideal  condition  is  to  have  the  plant  well  equipped  with  fruit  producing 
machinery  and  to  have  that  machinery  working  efficiently.  One  or  two 
further  parallels  may  be  drawn  at  this  point  between  the  living  plant  and 
the  hypothetical  manufacturing  establishment  with  which  it  has  been 
compared.  Good  equipment  with  fruit  producing  machinery  does  not 
mean  the  maximum  amount  that  can  be  crowded  into  the  available  room 
any  more  than  an  amount  plainly  inadequate  for  the  establishment.  Too 
much  fruiting  wood  unduly  taxes  the  tree  for  its  maintenance.     On  the 

388 


PRUNING  389 

other  hand  maximum  production  cannot  be  expected  from  a  half-equipped 
plant.  An  efficiently  working  machine  is  not  one  that  is  carrying  an  over- 
load any  more  than  it  is  one  carrying  half  or  a  third  of  a  load.  Regular, 
steady,  annual  production  of  large  but  not  maximum  amounts  is  desirable. 

Perhaps  in  certain  species  the  problem  of  securing  heavy  and  regular  fruit 
production  is  somewhat  simpler  than  has  been  indicated.  In  the  jaboticaba 
whose  blossoms  and  fruits  come  out  indiscriminately  anywhere  on  the  bark, 
from  the  crown  or  even  exposed  roots  to  the  tips  of  the  youngest  branches,  the 
question  of  developing  a  special  fruit  producing  mechanism  never  arises.  The 
plant  cannot  grow  without  developing  its  fruit  machinery  and  it  is  only  the 
proper  functioning  of  this  bark  that  is  a  limiting  factor  to  production.  Certain 
other  tropical  and  subtropical  fruits  present  other  apparent  exceptions  to  the 
general  statements  that  have  been  made,  but  they  need  not  be  given  serious  con- 
sideration here,  for  they  do  not  alter  materially  the  general  principles  involved 
or  their  application  in  deciduous  fruit  production. 

Therefore  it  is  desirable  to  determine  as  nearly  as  possible  the  exact 
nature  of  the  fruiting  habits  of  the  different  species  and  the  methods  by 
which  they  can  be  modified  and  controlled.  What  is  the  fruiting  mechan- 
ism of  the  various  fruits?  What  constitutes  an  adequate  equipment  for 
plants  of  different  sizes  or  ages?  How  can  the  amount  best  be  increased 
or  limited?  How  does  it  usually  function  under  varying  conditions? 
What  methods  can  be  employed  to  make  it  work  at  full  efficiency,  carry  a 
full  load,  year  after  year?  How  long  does  the  machinery  last?  What  are 
the  best  means  of  getting  rid  of  useless  or  inefficient  machinery  and  of 
securing  new  equipment?  When  is  it  best  to  attempt  to  repair  and  speed 
up  equipment  that  is  working  poorly  and  when  is  it  best  to  discard  it  and 
obtain  new?  The  answers  to  these  and  many  other  related  questions  are 
of  first  importance  to  the  grower,  for  profitable  production  depends  on 
them  to  no  small  degree. 


CHAPTER  XXI 
GROWING  AND  FRUITING  HABITS 

Left  to  themselves  the  plants  of  each  species,  or  even  of  each  variety 
show  more  or  less  distinctive  growing  and  fruiting  characteristics.  The 
former  are  partly  under  the  control  of  the  grower,  so  that  it  is  possible 
for  him  to  make  plants  of  quite  different  growing  habits  assume  a  nearly 
uniform  shape  in  the  orchard  or  to  train  two  of  the  same  kind  so  that  they 
appear  very  unlike.  His  control  over  bearing  habits  is  less  complete 
though  much  can  be  done  to  modify  them  in  certain  directions.  Both  are 
influenced  directly  or  indirectly  by  nearly  every  cultural  practice.  Prun- 
ing, however,  using  that  term  in  its  broader  sense,  is  the  most  direct  and 
most  important  of  these  practices. 

Some  growers  prune  their  trees;  some  do  not.  Others  prune  some  of 
their  fruit  trees,  but  leave  other  kinds  unpruned.  The  trees  or  plants  of 
certain  species  are  quite  generally  given  some  kind  of  pruning  treatment ; 
those  of  certain  other  species  are  almost  as  generally  let  alone.  In  some 
orchards  pruning  is  a  regular  annual  operation;  in  others  it  is  done  bienni- 
ally or  at  long  irregular  intervals.  There  is  no  horticultural  practice  con- 
cerning which  there  is  a  greater  diversity  of  opinion  or  in  the  application 
of  which  there  is  a  greater  diversity  of  procedure.  If  the  average  grower 
is  asked  why  he  prunes  or  why  he  does  not  his  answer  is  likely  to  be  that  he 
believes  it  is  good  for  the  tree  or  that  it  is  not  good  for  it.  Seldom  does  he 
give  specific  objects  that  he  has  in  mind  or  that  he  beheves  may  be  accom- 
plished by  means  of  pruning.  If  specific  objects  are  mentioned  they  are 
likely  to  be  among  the  following:  (1)  to  open  the  tree  so  that  the  fruit 
will  color  more  satisfactorily,  (2)  to  train  it  to  some  desired  form,  (3)  to 
remove  dead  or  diseased  limbs,  (4)  to  remove  water  sprouts,  (5)  to  thin 
the  fruit. 

All  of  these  are  accomplished  by  pruning  if  the  work  is  done  properly; 
nevertheless  they  are  not  its  primary  objects.  Fundamentally,  pruning, 
in  common  with  other  cultural  practices,  should  be  directed  to  encourage 
the  production  of  larger  quantities  of  fruit,  the  production  of  fruit  of 
better  grade,  or  to  lower  the  cost  of  production ;  its  value,  like  that  of 
any  other  orchard  operation,  may  be  determined  by  the  extent  to  which 
it  contributes  in  any  one  or  more  of  these  three  directions. 

Pruning  may  be  considered  from  many  points  of  view  and  subdivided 
in  many  ways.     In  the  following  discussion  it  is  considered  briefly  as  a 

390 


GROWING  AND  FRUITING  HABITS  391 

means  of  modifying  shape  and  in  more  detail  as  it  influences  development, 
location  and  functioning  of  the  fruiting  machinerj^  of  the  tree. 

PRUNING  FOR  FORM— TRAINING 

There  is  frequent  failure  to  distinguish  clearly  between  pruning  and 
training.  The  two  practices  are  often  regarded  as  one  and  the  same  or 
at  least  as  inseparable.  Training  concerns  form  primarily;  pruning 
affects  function  primarily.  Training  determines  the  general  character 
and  even  the  details  of  the  plant's  outline  and  of  its  branching  and  frame- 
work; pruning  is  meant  to  assist  more  in  determining  what  the  tree 
does  in  respect  to  fruiting.  Training  may  be  illustrated  by  reference 
to  what  may  be  done  easily  with  the  grape.  Without  cutting  off  or 
cutting  back  a  single  cane,  it  is  possible  to  train  a  vine  on  a  one-wire 
trellis,  a  two-wire  trellis,  a  three-wire  vertical  trellis,  a  three-wire  hori- 
zontal trellis,  an  arbor,  or  in  any  one  of  a  dozen  other  ways.  The 
training  simply  gives  the  vine  its  form  and  has  comparatively  little  to 
do  with  the  number  or  size  of  the  bunches  of  fruit  it  produces.  Similarly, 
fruit  trees  are  made  to  assume  one  form  or  another — for  example,  high- 
headed  or  low-headed,  open-centered  or  closed-centered,  flat-topped  or 
pyramidal — and  production  is  influenced  comparatively  little  by  these 
shapes.  It  is  true  that  the  pruning  saw  and  shears  are  generally  used  in 
forcing  the  trees  into  the  one  shape  or  the  other,  and  hence,  perhaps  the 
operation  should  be  spoken  of  as  "pruning  for  form."  Nevertheless 
the  operation  affects  form  principally  and  consequently  is  here  discussed 
under  the  heading  of  training,  even  though  strictly  speaking  the  use  of 
that  term  should  be  limited  to  such  changes  in  form  as  are  effected  with- 
out the  removal  of  parts.  If  parts  are  removed  at  such  a  time  and  in 
such  a  way  as  to  modify  materially  the  functioning  of  the  whole  tree  or  of 
some  of  its  parts,  even  though  its  general  shape  is  left  unchanged,  the 
operation  should  be  considered  pruning.  Many  times  both  shape  and 
function  are  modified  by  a  single  operation,  which  then  is  to  be  regarded 
as  both  pruning  and  training;  often,  however,  it  is  chiefly  one  feature  of 
the  tree's  growth  that  is  influenced. 

General  Objects. — In  general,  training  has  little  direct  effect  on 
the  amount  of  fruit  borne.  Some  of  the  pruning  practices  that  accom- 
pany certain  methods  of  training  may  affect  yields  profoundly,  but  the 
training  in  itself  is  of  only  secondary  importance  in  this  connection.  On 
the  other  hand  training  may  be  a  factor  in  determining  grade,  or  what 
is  frequently  referred  to  as  "  quality. "  Its  influence  on  grade  is  produced 
largely  through  making  it  difficult  or  easy  to  spray  thoroughly  and 
consequently  in  aiding  or  hindering  the  control  of  insects  and  diseases. 
Standard  control  measures  for  certain  pests  may  lose  half  of  their  effi- 
ciency if  the  plants  have  been  untrained  or  poorly  trained.  This  influ- 
ence is  distinct  from  and  additional  to  the  direct  control  of  certain  pests 


392  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

by  cutting  out  and  destroying  infected  parts.  In  certain  fruits  the 
shape  and  openness  of  the  tree  is  important  in  influencing  the  colora- 
tion. Training  is  important  also  in  reducing  certain  production  costs. 
Tillage  and  other  soil  treatments,  spraying,  thinning,  propping,  trellising 
and  harvesting  all  may  be  greatly  facilitated  by  proper  training. 

In  a  general  way  training  should  tend  so  to  distribute  the  fruiting 
wood  and  the  fruit  that  all  orchard  or  vineyard  operations  may  be  con- 
ducted with  greatest  facility  and  lowest  cost.  It  should  eliminate  or 
minimize  the  necessity  and  cost  of  trellising,  propping,  or  artificially 
supporting  the  plant  and  its  fruit.  It  should  provide  the  leaves  and 
developing  fruits  with  as  nearly  as  possible  optimum  conditions  for 
coloration  without  danger  from  sunscald  and,  wherever  feasible,  it 
should  aim  to  provide  those  conditions  least  favorable  for  the  work  of 
injurious  insects  and  diseases.  In  view  of  all  these  possible  effects  of 
training  and  of  the  widely  varying  conditions  under  which  plants  of  even 
the  same  variety  are  grown,  it  is  evident  that  the  best  method  of  training 
a  plant  in  one  situation  may  be  quite  distinct  from  what  is  best  in 
another  and  it  often  happens  that  two  fruits  or  two  varieties  of  the  same 
fruit  should  be  trained  differently  when  grown  in  the  same  environment. 

Since  the  training  of  trees  presents  certain  problems  quite  distinct 
from  those  of  pruning  it  seems  desirable  to  consider  them  separately 
from  their  possible  influence  on  function. 

Details  in  Training. — A  comparatively  large  part  of  the  training 
that  trees  are  to  receive  should  be  given  during  the  first  few  years  of 
their  growth.  It  is  during  this  period  that  they  are  building  their  frame- 
work and  taking  on  the  general  form  that  the  grower  has  decided  shall 
be  theirs  during  the  rest  of  their  lives.  During  later  years  efforts  are 
directed  mainly  to  preserve  the  form  already  given  the  tree  and  attention 
is  given  to  its  pruning  as  distinguished  from  training. 

Height  of  Head. — By  height  of  head  is  meant  the  distance  from  the 
ground  at  which  the  main  or  scaffold  limbs  branch  from  the  trunk. 
Trees  in  which  the  scaffold  limbs  come  out  within  23^^  or  3  feet  from  the 
ground  are  spoken  of  as  low-headed;  those  in  which  they  come  out  from 
the  trunk  4  feet  or  more  from  the  ground  are  high-headed.  The  height 
of  head  generally  is  established  at  the  time  of  setting  by  the  distance 
from  the  ground  at  which  the  top  is  cut  off  though  it  is  possible  to  raise 
the  head  or  sometimes  to  lower  it  by  later  treatment.  In  the  older 
orchards  high-headed  trees  are  the  rule.  It  was  thought  that  high- 
heading  facihtated  cultivation  and  other  orchard  operations  and  perhaps 
was  better  for  the  tree.  More  recent  tendencies  have  been  in  the 
direction  of  lower  heads.  If  properly  handled  it  is  no  more  difficult  to 
cultivate  around  and  under  such  trees  and  pruning,  spraying,  thinning 
and  picking  are  greatly  facilitated.  Furthermore,  low-headed  trees  are 
less  subject  to  sunscald  and  suffer  less  from  high  winds. 


GROWING  AND  FRUITING  HABITS  393 

Number  of  Scaffold  Limbs. — The  number  of  scaffold  limbs  found  in 
orchard  trees  varies  from  2  to  15  or  20.  Neither  extreme  is  desirable. 
If  there  are  only  two  or  three  main  scaffold  limbs  they  are  almost  certain 
to  form  crotches  that  are  likely  to  split  and  allow  one  or  both  parts  to 
break  down.  A  large  percentage  of  the  injury  resulting  from  trees  break- 
ing when  heavily  loaded  with  fruit  or  when  subjected  to  severe  winds 
is  due  indirectly  to  sharp  crotches  that  could  have  been  avoided  by  the 
use  of  more  and  better  spaced  scaffold  limbs.  Should  one  limb  of  a 
group  of  three  split  down,  a  third  of  the  tree  is  gone;  should  one  of  eight 
be  lost,  most  of  the  tree  still  remains  and  the  injury,  which  is  much  less 
likely  to  happen,  is  more  readily  repaired.  On  the  other  hand  too  many 
scaffold  limbs,  as  10  to  12,  give  rise  to  thick,  brushy  tops  that  make 
work  in  them  difficult.  A  moderate  number,  five  to  eight,  makes  a 
tree  that  is  mechanically  strong  and  at  the  same  time  open  enough  to 
facilitate  necessary  orchard  operations. 

Distribution  of  Scaffold  Limbs. — Of  still  greater  importance  than  the 
number  of  scaffold  limbs  is  their  distribution.  When  they  come  out  from 
the  trunk  at  points  close  together,  as  for  instance,  when  the  upper  one  of 
five  is  onl}^  8  or  10  inches  above  the  lowest  they  form  bad  crotches  much 
sooner  than  if  they  are  distributed  over  a  longer  distance  on  the  trunk. 
When  they  are  distributed  over  11^  or  2  feet  of  the  trunk  each  limb  has 
a  chance  to  make  more  or  less  "  shoulder;"  weak  crotches  with  subsequent 
splitting  are  avoided.  It  may  require  a  little  attention  to  select  and 
develop  scaffold  limbs  that  are  separated  well  from  one  another,  on 
account  of  the  tendencj^  of  the  tree  to  make  its  most  vigorous  growth 
from  buds  near  the  end  of  the  trunk  or  near  the  extremities  of  its  branches 
but  it  is  well  worth  while.  Furthermore,  it  should  be  remembered  that 
the  distribution  of  these  limbs  is  determined  once  and  for  all  by  the  first 
two  or  three  prunings  and  no  amount  of  later  work  will  entirely  correct 
a  mistake  made  then.  If  a  tree  is  headed  at  a  height  of  33  to  36  inches 
it  is  possible  to  have  a  good  number  of  well-distributed  limbs  and  at  the 
same  time  have  a  low-headed  tree.  One  of  the  main  advantages  of  the 
"modified  leader"  type  of  training  is  the  opportunity  for  a  wide  spacing 
of  the  scaffold  limbs. 

Ope7i  and  Closed-centered  Trees. — There  has  been  much  discussion  over 
the  relative  merits  of  open-centered  or  vase-shaped  and  close-centered 
or  leader  trees.  Both  forms  have  their  advocates.  Both  are  extensively 
used  and  both  are  successful — good  evidence  that  the  exact  form  in  which 
trees  are  trained  is  a  matter  of  secondary  importance  from  the  standpoint 
of  production.  Theoretically  at  least,  the  open-centered  method  of 
training  admits  more  sunlight  and  thus  enables  the  fruit  to  attain  a 
higher  color  than  is  possible  in  the  closed-centered  tree,  though  in  reality 
the  tree  that  is  started  with  the  open  center  is  often  allowed  to  become 
more  thick-topped  than  many   "leader"  trees.     Obviously,   this  is  a 


394  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

matter  that  can  be  of  no  real  importance  in  fruits  where  coloration  does 
not  depend  on  the  light  reaching  the  fruit  itself.  From  the  very  nature  of 
the  case  the  central-leader  type  of  tree  forms  more  scaffold  limbs  than  the 
open-centered  tree  and  consequently  it  is  less  likely  to  split  at  the  crotches. 
It   is   often   more   bushy-topped   but  this   condition   is  not  necessary. 

It  has  become  a  generally  accepted  practice  to  train  certain  fruits  in 
certain  styles.  For  instance,  peaches  are  almost  always  grown  in  the 
vase  form  and  pears  are  trained  with  a  central  leader.  In  some  cases 
whole  sections  use  a  certain  style  for  practically  all  their  tree  fruits.  To 
what  extent  these  practices  are  based  on  careful  comparisons  of  different 
methods  of  training  for  the  fruit  or  the  locality  in  question  and  to  what 
extent  they  are  followed  simply  because  the  custom  has  become  estab- 
lished is  often  difficult  to  say.  A  careful  study  of  training  methods  might 
lead  in  many  cases  to  some  change  that  would  be  of  considerable  com- 
mercial importance  to  the  particular  district  or  for  the  particular  variety. 

The  general  method  of  procedure  in  training  a  tree  to  the  central- 
leader  type  is  each  year  to  prune  back  the  central  and  upper  shoot  or 
leader  less  severely  than  the  lateral  shoots  or  hmbs  surrounding  it.  If  an 
open-centered  tree  is  desired  the  opposite  method  should  be  followed. 
It  is  a  mistake  in  attempting  to  train  a  tree  to  the  open-centered  type 
to  cut  out  entirely  the  interior  and  central  limbs.  This  merely  provokes 
the  production  of  water  sprouts  to  take  their  place  and  more  cutting  out 
must  be  done.  By  cutting  back  the  interior  and  upper  shoots  and  limbs 
more  severely  than  the  outer,  the  former  are  subordinated  and  the  latter 
are  made  the  dominant  limbs  in  the  tree.  In  other  words,  it  is  easier 
and  better  to  grow  an  open-centered  tree  with  a  comparatively  open 
center — with  only  a  few,  small,  subordinate,  fruiting  branches  in  the 
interior — than  one  with  a  completely  open  or  hollow  center. 

A  different  type  of  training  that  is  coming  into  favor  is  known  as 
the  "modified  leader."  As  the  name  suggests,  it  is  intermediate  between 
the  open-centered  and  the  leader  tree.  It  is  developed  by  training  to  the 
leader  type  for  the  first  4  or  5  years  and  from  then  on  as  an  open-centered 
tree.  This  results  in  a  tree  with  a  central  leader  extending  some  3  to  5 
feet  above  the  point  where  it  was  originally  headed  and  then  an  open 
center  above  that.  It  possesses  practically  all  the  advantages  of  the  two 
other  types  and  few  or  none  of  their  disadvantages. 

Trees  of  Different  Shape. — Less  attention  need  be  devoted  to  the 
general  shape  of  the  tree  than  to  certain  other  features  of  its  training. 
Nevertheless,  there  are  occasional  arguments  for  flat-topped  or  round- 
topped  trees  or  other  forms.  In  general,  little  emphasis  should  be  placed 
on  these  particular  shapes.  It  is  not  a  bad  plan  to  allow  the  tree  con- 
siderable freedom  in  assuming  the  general  shape  that  is  natural.  Training 
for  form  should  be  limited  to  correcting  minor  defects  rather  than  altering 
profoundly  the  shape. 


GBOWING  AND  FRUITING  HABITS  395 

Lowering  the  Tops  of  Trees. — In  the  course  of  time  the  trees  of  many 
species  become  so  tall  that  the  added  cost  of  gathering  the  fruit  from  the 
topmost  branches  reduces  the  margin  of  profit  to  the  vanishing  point. 
Furthermore  the  higher  branches  shade  the  lower  and  reduce  their  effi- 
ciency as  fruit  producers.  The  increased  difficulty  in  controlling  insects 
and  diseases  in  the  tops  of  very  tall  trees,  even  with  the  aid  of  the  best  of 
the  present  power  spraying  outfits,  makes  those  portions  of  doubtful 
value  to  the  grower  even  though  it  should  be  possible  to  harvest  the 
fruit  economically.  One  investigator  sets  25  feet  as  about  the  limit 
in  height  for  profitable  apple  production '^  ^nd  with  the  smaller  spraying 
outfits  the  limit  is  probably  well  below  that  figure.  The  problem  of 
controlling  the  height  of  trees  and  keeping  their  lower  branches  actively 
producing  a  good  grade  of  fruit  is  thus  very  real. 

Many  growers  wait  until  the  trees  get  much  too  tall  for  profit  and  then 
"dehorn;"  that  is,  they  cut  back  the  limbs  severely,  leaving  large  stubs 
that  promptly  send  out  an  abundance  of  strong  vigorous  watersprouts. 
Eventually  new  fruiting  wood  is  developed  from  this  new  growth,  but  in 
the  meantime  crowding  is  likely  to  force  this  new  growth  up,  so  that  by 
the  time  the  top  has  been  bearing  a  few  years  it  is  too  high  again  and 
another  dehorning  becomes  necessary. 

A  much  better  method  of  lowering  the  tops  of  tall  trees  is  to  cut  back 
into  2-,  3-,  or  4-year-old  wood,  always  to  a  lateral  branch.  The  more 
nearly  horizontal  this  side  limb,  the  better.  By  thus  cutting  to  a  lateral 
the  flow  of  sap  is  utilized  in  a  somewhat  increased  growth  and  few  or  no 
watersprouts  develop.  A  year  or  two  later  this  lateral  can  be  cut  back 
to  one  of  its  side  branches,  or  perhaps  the  whole  structure  can  be  removed, 
the  cut  being  to  a  still  lower  side  limb  on  the  main  branch  that  in  the  mean- 
time has  been  strengthened  by  the  heading  back  of  the  season  before. 

This,  it  will  be  recognized,  is  a  procedure  aiming  constantly  to  keep 
the  tree  within  bounds  rather  than  permitting  it  first  to  become  far  too 
tall  and  then  greatly  reducing  its  height.  To  be  most  successful  it 
should  begin  when  the  tree  reaches  about  the  desired  height  and  from 
then  on  it  should  constitute  a  part  of  the  regular  annual  treatment  that 
the  tree  receives.  It  will  not  be  necessary  to  lower  every  part  or  limb 
of  every  tree  each  year;  only  the  tallest,  those  getting  too  high,  need  be 
cut  back.  This  practice  not  onlj^  results  in  the  production  of  fewer 
watersprouts  but  it  keeps  the  lower  part  of  the  tree  in  a  better  producing 
condition  than  is  possible  with  occasional  dehorning.  It  is  a  heading 
back  in  name  mainly — really  resulting  in  more  thinning  than  cutting 
back — and  is  followed  by  the  kind  of  a  response  that  attends  thinning 
out. 

Eliminating  and  Subordinating  Limbs. — It  has  just  been  stated  that 
in  the  training  of  open-centered  trees  it  is  usually  better  to  suppress  or 
subordinate  the  interior  limbs  than  to  attempt  their  total  elimination. 


396  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

This  last  can  be  done  by  cutting  them  out  and  then  repeatedly  removing 
watersprouts  that  take  their  place,  but  this  involves  much  labor.  If 
they  are  subordinated  the  water  sprout  problem  is  largely  eliminated 
and  they  may  serve  as  fruit-producing  branches  for  many  years.  In 
apples,  pears  and  other  spur-bearing  fruits,  their  retention  may  also  aid 
materially  in  bringing  the  trees  into  bearing  earlier,  because  if  properly 
handled  they  develop  fruit  spurs  and  fruit  buds  freely  at  a  period  when 
heavy  pruning  back  for  proper  form  may  prevent  to  a  great  extent 
formation  of  spurs  on  the  more  permanent  framework  of  the  tree.  Often 
one  of  the  best  ways  to  subordinate  and  make  fruiting  branches  from 
these  interior  limbs  is  to  let  them  remain  with  no  heading  back  at  the 
beginning  of  their  second  season.  They  then  produce  short  vegetative 
growths  from  their  terminal  buds,  with  few  or  no  lateral  shoots  but  with 
many  lateral  spurs.  After  their  second  season's  growth  they  are  headed 
back  into  2-year-old  wood.  Treated  in  this  way  they  make  but  little 
further  shoot  growth  and  little  difficulty  is  experienced  in  keeping  them 
as  subordinate  fruit-bearing  limbs. 

Preventing  the  Formation  of  Crotches. — It  is  a  principle  of  rather  gen- 
eral application  that  the  unequal  cutting  back  of  two  parts  in  the  same 
tree  or  plant  tends  to  subordinate  that  part  pruned  more  severely  and 
to  give  the  advantage  to  the  other.  Equal  cutting  of  two  shoots  or 
limbs  of  about  the  same  length  results  in  their  equal  subsequent  develop- 
ment into  a  fork  or  crotch  that  is  a  point  of  weakness  in  the  framework  of 
the  tree.  Crotches  can  be  largely  avoided  and  the  framework  corre- 
spondingly strengthened  by  pruning  with  the  idea  of  making  one  of  two 
equal  branches  a  leader  and  the  other  a  lateral  subordinate  to  it. 

BEARING  HABITS 

There  is  reason  to  believe  that  with  proper  nutritive  conditions  in  the 
plant,  particularly  with  an  accumulation  of  certain  carbohydrates,  any 
partly  developed  bud  may  undergo  differentiation,  form  flower  parts 
and  develop  as  a  fruit  bud.  This  assumes  that  other  limiting  factors, 
such  as  moisture  and  temperature,  are  favorable.  It  is  conceivable  that 
in  the  developing  buds  of  some  plants  a  stage  is  finally  reached  when 
such  a  differentiation  cannot  take  place  except  by  the  unfolding  of  the 
bud  into  a  leafy  structure  and  the  subsequent  formation  of  the  fruit  bud 
at  a  new  growing  point.  In  general,  though,  every  bud  is  to  be  regarded 
as  a  potential  flower  bud.  In  every  kind  of  plant,  however,  most  of  the 
flower  buds  are  formed  in  certain  definite  positions,  probably  because  it 
is  only  in  those  positions  that  nutritive  and  other  conditions  favorable 
for  flower  bud  formation  ordinarily  occur.  It  is  therefore  possible  to 
speak  of  the  bearing  or  fruiting  habit  of  a  plant,  though  the  use  of  this 
term  does  not  mean  that  other  types  of  bearing,  other  fruiting  habits, 
may  not  be  found  on  the  same  plant  under  unusual  conditions.     Not 


GROWING  AND  FRUITING  HABITS  397 

infrequently  the  crop  borne  from  flowers  appearing  in  such  an  unusual 
place  exceeds  that  produced  by  those  considered  characteristic.  For 
instance,  the  nectarine  would  be  classed  generally  as  a  tree  bearing  its 
fruit  buds  laterally  on  shoots,  but  the  Stanwick  variety  is  as  typical  a 
spur  bearer  as  the  Montmorency  cherry. 

Since  all  buds  are  to  be  regarded  as  potential  flower  buds,  flowers  or 
inflorescences  and  hence  fruits,  may  be  borne  wherever  buds  are  borne — 
usually  (1)  terminally  on  long  or  short  growths,  or  (2)  laterally  in  the 
axils  of  the  current  or  past  season's  leaves  and  now  and  then  (3)  adven- 
titiously from  any  point  on  the  exposed  bark  of  limbs,  trunks  or  roots. 
As  a  rule  the  position  of  the  flower  or  inflorescence  on  the  shoot  relative 
to  the  growth  of  the  current  season  is  characteristic  of  the  species  or 
variety  and  is  subject  to  but  little  change.  The  inflorescences  of  the 
raspberry  and  blackberry  are  always  terminal  to  the  growth  of  the  current 
season  and  the  flowers  or  inflorescences  of  the  persimmon  are  always 
lateral.  Flower-bearing  shoots  may  arise  from  either  terminal  or  lateral 
buds  on  either  long  or  short  growths  (spurs),  or  they  may  arise  from 
adventitious  buds.  There  is  often  considerable  variation  within  the 
species,  variety,  or  even  individual  plant  in  this  respect. 

Relation  of  Growth  Habits  to  Position  of  Fruit  Buds. — Within  limits 
certain  habits  of  growth  are  necessitated  by  or  at  least  are  associated  with, 
particular  fruiting  habits.  In  general,  plants  with  terminal  fruit  buds 
have  a  somewhat  restricted  habit  of  growth.  Terminal  bearing  tends  to 
promote  greater  compactness  of  tree  or  plant  than  bearing  from  lateral 
fruit  buds,  because  it  forces  the  development  of  laterals  from  below, 
rather  than  beyond,  the  flowers  or  flower  clusters.  Plants  whose  fruit 
buds  are  borne  either  terminally  (apple)  or  laterally  (sweet  cherry)  on 
short  growths  or  spurs  are  generally  more  compact  than  those  like  the 
peach  or  grape  whose  fruit  buds  are  borne  on  long  shoots  and  the  problem 
of  preventing  their  bearing  areas  from  getting  too  far  away  from  the 
trunk  or  head  of  the  plant  is  less  serious.  If  fruit  buds  are  borne  later- 
ally on  long  shoots  there  may  be  a  distinct  difference  in  the  general  man- 
ner of  growth,  depending  on  whether  they  are  found  principally  on  the 
basal,  median  or  distal  portion  and  the  grower  will  employ  a  "short," 
"medium"  or  "long"  pruning  system,  as  the  case  may  be. 

Different  Kinds  of  Flower-bearing  Shoots. — Regardless  of  the  location 
of  the  fruit  bud — that  is,  whether  terminal  or  lateral — when  it  unfolds  it 
may  give  rise  to  any  one  of  three  distinct  types  of  flower-bearing  struc- 
tures: (1)  it  may  contain  flower  parts  only  and  develop  a  single  flower 
(as  in  the  peach)  or  a  flower  cluster  (as  in  the  cherry)  without  leaves,  (2) 
it  may  be  a  mixed  bud  and  develop  a  short  or  long  leafy  shoot  terminating 
in  an  inflorescence  (as  in  the  apple),  (3)  it  may  be  mixed  and  develop  a 
short  or  long  leafy  shoot  bearing  flowers  or  flower  clusters  in  some  of  its 
leaf  axils  (as  in  the  persimmon). 


398  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Classification  of  Fruits  According  to  Fruiting  Habits 


Fruit  buds  terminal 

Fruit  buds  lateral 

I 

IV 

Flower  bud  containing 

Loquat 

Peach 

flower  parts  only 

Mango 

Plum 

Apricot 

Cherry 

Almond 

Plumcot 

Currant 

Gooseberry 

Kumquat 

Northern  papaw 

Walnut  (staminate  catkins) 

Hickory  (staminate  catkins) 

Pecan  (staminate  catkins) 

II 

V 

Flower  bud  mixed 

Apple  (principally) 

Blackberry 

Flowering    shoot     with 

Pear     (principally) 

Raspberry 

terminal  inflorescences 

Quince 

Dewberry 

Medlar 

Grape 

Hawthorn 

Filbert 

Haw 

Blueberry 

Elder 

Cranberry  (European) 

Juneberry 

Cashew  nut 

Walnut  (pistillate  flowers) 

Brazil  nut 

Hickory  (pistillate  flowers) 

Pond-apple      (and      various 

Pecan  (pistillate  flowers) 

other  anonaceous  fruits) 
Apple  (occasionally) 
Pear  (occasionally) 

III 

VI 

Flower  bud  mixed 

Guava 

Persimmon 

Flowering    shoot    with 

Tropical  almond 

Mulberry 

lateral  inflorescences 

Rose-apple  (.and  other  species 

Fig 

of  Eugenia) 

Cranberry  (American) 

Olive  (partly) 

Chestnut 

Chinquapin 

Oak 

Beech 

Pistachio 

Star-apple 

Jujube 

Avocado 

Olive  (partly) 

GROWING  AND  FRUITING  HABITS  399 

A  Classification  of  Plants  According  to  Bearing  Habits. — Since  the 
flower  bud  itself  is  either  terminal  or  lateral,  there  are  six  main  types  of 
fruiting,  six  distinct  bearing  habits,  the  classification  being  based  upon 
the  location  of  the  fruit  buds  and  the  type  of  flower-bearing  structure  to 
which  they  give  rise.  These  six  main  groups  together  with  the  more 
important  of  the  fruits  they  include  are  shown  in  the  accompanying 
diagram. 

There  are  endless  variations  within  these  main  groups;  certain 
species  or  varieties  sometimes  bear  in  one  way  and  sometimes  in  another, 
or  in  two  or  more  ways  at  the  same  time. 

The  following  discussion  points  out  some  of  the  peculiarities  of  the 
more  important  fruits.  Several  special  groups  also  are  included  to  bring 
together  those  fruits  having  in  their  bearing  habits  certain  peculiarities 
that  make  it  desirable  to  consider  them  separately  from  the  main  groups 
to  which  they  might  be  referred. 

Group  I. — Fruit  buds  borne  terminally,  containing  flower  parts  only 
and  giving  rise  to  inflorescences  without  leaves. 

None  of  the  common  deciduous  fruits  has  this  bearing  habit.  It  is  best 
illustrated  perhaps  by  the  loquat  and  the  mango  (see  Fig.  39).  Growth  is  con- 
tinued by  branches  rising  from  lateral  buds  below  the  inflorescence;  some  of  these 
branches  form  terminal  buds  for  a  succeeding  crop.  The  indications  are  that  in 
the  mango  fruit  bud  differentiation  does  not  take  place  long  before  the  flowering 
season  and  sometimes  two,  three  or  even  four  crops  of  flowers  are  formed  during 
the  year,  though  this  is  not  hkely  if  there  is  a  good  set  of  fruit  which  is  carried 
through  to  maturity.  In  case  some  accident  happens  to  the  terminal  flower  bud 
of  the  mango,  some  of  the  a.xillary  buds  may  differentiate  flower  parts  and  thus 
form  fruit  buds. 

Group  II. — Fruit  buds  borne  terminally,  unfolding  to  produce 
leafy  shoots  that  terminate  in  flower  clusters. 

This  bearing  habit  is  characteristic  of  most  of  the  pome  fruits  and  is 
found  likewise  in  a  few  others  of  minor  economic  importance. 

In  the  apple  and  pear  most  of  the  terminal  fruit  buds  are  on  spurs, 
(see  Fig.  40)  though  in  young  vigorous  trees  of  certain  varieties  many 
of  the  long  shoots  form  terminal  flower  buds.  Seldom,  however,  is  any 
considerable  percentage  of  the  crop  borne  in  this  latter  way.  The  fruit 
buds  of  these  plants  are  mixed  and  invariably  give  rise  to  very  short 
growths  with  a  few  short  internodes,  leaves  of  ordinary  size  and  a  lateral 
branch  (sometimes  two  or  more)  arising  in  the  axil  of  one  of  the  leaves;  this 
branch  may  bear  fruit  the  following  season,  though  usually  fruit  bud 
formation  is  delayed  a  year  or  more.  The  spur  may  live  a  great  many 
years  and  bear  repeatedly.  The  actual  records  of  individual  spurs 
generally  show  an  irregularly  alternate  bearing  habit.  New  spurs  origi- 
nate from  lateral  buds  on  shoots  of  the  preceding  season  and  occasionally 
from  latent  or  adventitious  buds  on  the    trunk  or  older  limbs.     The 


400  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

continued  bearing  of  the  individual  spurs  makes  for  a  comparatively 
compact  type  of  tree  growth. 

The  juneberrj^  or  shadbush  (Amelanchier)  and  hawthorn  or  azarole  {Cratoe- 
gus)  have  bearing  habits  practically  identical  with  those  of  the  apple  and  pear 
just  described. 

Mention  should  be  made  that  both  the  apple  and  pear  occasionally  bear 
lateral  fruit  buds  on  long  shoots.  Certain  varieties,  like  Wagener,  are  particu- 
larly given  to  this  habit.  It  is  found  more  frequently  in  young  vigorous  trees 
than  in  those  with  a  settled  bearing  habit.  However,  the  fact  that  it  may  occur 
on  almost  any  variety  and  that  occasionally  a  considerable  percentage  of  the 
crop  may  be  borne  in  this  way,  is  evidence  that  this  habit  is  a  response  to  unusual 
nutritive  conditions.  The  special  treatment  that  should  be  accorded  trees 
fruiting  in  this  manner  is  discussed  under  Pruning  of  the  Apple  and  Pear. 


/ 
Figs.  39-42. — Diagrams  showing  (from  left  to  right)  bearing  habits  of  loquat,  apple 
olive  and  peach.     F  equals  fruit;  B  equals  flower  bud;  L  equals  leaf  bud.     One-year-old 
wood  shown  by  solid  line,  two-year-old  wood  by  broken  line. 

The  bearing  habit  of  the  quince  and  the  medlar  is  similar  to  that  of  the 
apple  and  pear,  except  that  when  the  terminal  (mixed)  fruit  bud  unfolds 
it  gives  rise  to  a  leafy  shoot  of  medium  length,  with  medium  long  instead 
of  short  internodes  and  the  flowers  are  borne  terminally  on  this  shoot. 
Fruit  buds  for  the  following  season's  production  are  borne  terminally  on 
shoots  springing  from  lateral  buds  on  either  flowering  or  non-flowering 
shoots,  or  from  terminal  buds  on  older  shoots  that  the  year  before  did  not 
differentiate  flower  buds.  These  fruits  consequently  are  not  such  com- 
pact growers  as  the  apple  or  pear,  though  the  shorter  growth  of  their 
purely  vegetative  shoots  and  the  greater  tendency  for  their  lateral  buds  to 
grow  rather  than  remain  latent  may  give  them  a  very  thick  and  brushy 
appearance. 

The  haw  {Viburnum),  elder  (Sambunis),  and  clove  (Caryophyllus  aromaticus) 
have  bearing  habits  similar  to  the  quince  and  medlar,  though  occasionally  they 
differentiate  flower  buds  terminally,  like  the  apple  and  pear  on  short  growths, 
which  are  essentially  spurs.  All  these  fruits  are  opposite-leaved  and  it  fre- 
quently happens  that  the  lateral  buds  in  the  axils  of  the  upper  leaves  differenti- 
ate flower  parts.  This  is  more  likely  to  happen  if  the  terminal  bud  is  injured  or 
destroved. 


GROWING  AND  FRUITING  HABITS  401 

Group  III. — Fruit  buds  borne  terminally,  unfolding  to  produce 
leafy  shoots  with  flowers  or  flower  clusters  in  the  leaf  axils. 

This  might  be  called  an  incomplete  terminal  bearing  habit,  for  the 
fruit  itself  is  not  borne  terminally,  but  is  lateral  to  the  growths  upon  which 
it  appears.  However,  the  flower  buds  are  terminal.  The  terminal  buds 
of  the  flowering  shoots  may  differentiate  flower  parts  for  the  following 
year's  production  or  new  buds  may  develop  from  lateral  leaf  buds. 

None  of  the  common  deciduous  fruits  has  this  bearing  habit.  It  is  found  in 
the  pomegranate,  the  tropical  ahnond  {Terminalia  catappa),  the  guavas  {Psidium 
spp.),  the  olive,  and  in  a  number  of  the  species  of  Eugenia.  In  the  pomegranate, 
guava  and  in  the  Eugenias  the  fruit  buds  are  formed  on  short  shoots  or  spurs 
and  the  flowers  and  fruits  in  the  axils  of  the  outermost  leaves.  In  the  oUve  the 
inflorescences  are  generaUy  found  in  the  axils  of  the  shoot's  lower  leaves  and 
flowering  shoots  sometimes  spring  from  lateral  as  well  as  terminal  buds  (see  Fig. 
41).  The  tropical  almond  {Terminalia)  has  a  somewhat  })eculiar  growing  and 
fruiting  habit,  the  terminal  mixed  flower  buds  being  formed  on  the  ends  of  long 
shoots.  When  these  unfold  they  give  rise  to  short  growths  or  spurs,  in  the  axils 
of  whose  upper  leaves  flowers  and  fruits  are  borne.  The  long  growths  or  shoots 
originate  from  lateral  buds. 

Group  IV. — Fruit  buds  borne  laterally,  containing  flower  parts  only 
and  giving  rise  to  inflorescences  without  leaves  or  if  leaves  are  present 
they  are  much  reduced  in  size. 

In  the  peach,  lateral  fruit  buds  are  formed  on  the  long  shoots  (see 
Fig.  42).  Two  additional  or  supernumerary  leaves  commonly  appear 
at  many  nodes  as  the  season  progresses  and  fruit  buds  develop  in  their 
axils.  The  bud  in  the  axil  of  the  original  leaf  generally  remains  a  leaf 
bud;  rarely  it  too  differentiates  flower  parts.  This  whole  structure  may 
possibly  be  considered  a  much  reduced  secondary  growth.  Often  only  a 
single  extra  leaf  develops  at  the  node,  in  which  case  only  one  fruit  bud 
forms  at  that  point,  that  in  the  axil  of  the  supernumerary  leaf.  The 
peach  also  forms  fruit  buds  on  secondary  or  even  on  tertiary  lateral 
branches.  As  a  rule  when  the  fruit  buds  occur  on  the  upper  or  outer 
portions  of  secondary  shoots  and  sometimes  on  the  primary  shoots,  they 
are  single,  being  differentiated  from  the  bud  in  the  axil  of  the  single  leaf. 
They  are  quite  likely  to  be  in  pairs  at  the  more  basal  nodes.  As  already 
stated,  the  flower  buds  of  the  peach  are  usuallj^  produced  on  what  would 
be  called  long  growths  or  shoots,  though  under  certain  cultural  and  prun- 
ing treatments  many  varieties  form  short  laterals  that  are  comparable 
to  spurs  in  every  way.  The  flower  bud  of  the  peach  produces  only  one 
flower.     Growth  is  continued  b}^  terminal  or  by  lateral  leaf  buds. 

The  sweet  cherries  and  the  Domestica  and  Insititia  groups  of  plums 
form  their  flower  buds  for  the  most  part  laterally  on  spurs  (see  Fig. 
43).     These  come  from  lateral  buds  on  the  shoots  of  the  preceding  season 


402  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

and  their  new  shoots  form  both  terminal  and  lateral  buds  on  shoots  or  on 
older  wood. 

The  almond,  apricot,  plumcot,  the  Japanese  and  American  plums,  the 
sour  cherry,  the  currant  and  the  gooseberry  have  a  fruiting  habit  which  is 
a  combination  of  that  of  the  peach  on  the  one  hand  and  the  sweet  cherry 
on  the  other.  They  bear  in  both  ways,  though  certain  varieties  may 
show  a  greater  tendency  in  the  one  direction  or  the  other.  As  a  rule, 
frmt-bud  production  on  shoots  gradually  gives  way  to  production  on 
spurs  as  the  plants  become  older  and  less  vigorous.  Supernumerary  fruit 
buds  are  produced  freely  at  the  nodes  of  the  long  vigorous  shoots  of  Japanese 
and  American  plums  and  in  the  currant  and  gooseberry. 


•a 


ti^ 


Figs.  43-45. — Diagrams  showing  (from  left  to  right)  bearing  habits  of  sweet  cherry, 
raspberry  and  grape. 

The  kumquat  (Citrus  Japonica)  and  the  northern  pawpaw  (Asimina  triloba) 
differentiate  their  flower  buds  in  the  axils  of  the  leaves  on  long  shoots  of  the 
current  season  and  the  following  season  these  buds  give  rise  to  leafless  inflores- 
cences. This  bearing  habit  corresponds  to  that  of  the  sweet  cherry,  except  that 
production  of  the  flower  buds  is  on  long  rather  than  on  short  growths. 

Group  V. — Fruit  buds  borne  laterally,  unfolding  to  produce  leafy 
shoots  that  terminate  in  flower  clusters. 

The  blackberry,  raspberry,  dewberry  and  their  hybrids  form  fruit 
buds  either  on  primary  shoots  that  come  up  from  their  crowns  or  roots 
each  year,  or  on  their  secondary  lateral  shoots  (see  Fig.  44).  These 
flower  buds  develop  into  leafy  shoots  with  terminal  inflorescences  and 
individual  flowers  or  flower  clusters  in  the  leaf  axils.  In  most  varieties 
the  entire  cane  dies  after  bearing  and  growth  is  continued  by  the  forma- 
tion of  new  canes  springing  from  the  crown  or  roots. 

In  the  unopened  flower  bud  of  the  grape  (see  Fig.  45),  the  inflores- 
cence is  terminal  to  a  leafy  shoot  also  within  the  bud,  like  that  of  the 
raspberry  and  blackberry.  As  the  bud  opens,  however,  the  bud  in  the 
axil  of  the  topmost  leaf  of  this  developing  shoot  unfolds  and  continues 
the  growth  of  the  shoot.  This  results  in  pushing  the  flower  cluster  to 
one  side  so  that  the  inflorescence  appears  lateral  and  opposite  a  leaf. 
Several  flower  clusters  are  formed  terminally  at  successive  intervals  on 


GROWING  AND  FRUITING  HABITS 


403 


the  same  shoot  and  in  turn  are  crowded  to  one  side  and  hence  to  appar- 
ently lateral  positions.  As  a  rule  only  certain  branches  or  canes  of  the 
grape  bear  lateral  buds  that  differentiate  flower  parts.  These  branches 
or  canes  usually  arise  from  buds  near  the  base  or  in  the  median  portion 
of  bearing  shoots.  What  appears  to  be  the  bud  or  "eye"  of  the  grape 
really  consists  of  two  or  three  buds  within  the  one;  a  well  developed 
central  shoot  and  one  or  two  less  highly  developed  lateral  growing  points. 
In  case  the  central  bud  develops  prematurely  and  is  killed  by  frost,  its 
place  may  be  taken  by  another  of  the  group.  Occasionally  the  grape 
produces  flowering  shoots  from  latent  or  adventitious  buds. 

In  the  filbert,  which  has  no  ti-ue  terminal  buds,  some  of  the  more 
apical  lateral  buds  develop  into  short  leafy  shoots  ending  in  clusters  of 
pistillate  flowers  (see  Fig.  46).  Other  lateral  buds  grow  out  into  dwarf 
shoots,  which  are  without  normal-sized  leaves,  are  branched  and  really 
constitute  the  male  inflorescences.  These  remain  dormant  until  winter 
or  early  spring  when  they  open  to  discharge  their  pollen.     At  the  base 


Figs.  46-48. — Diagrams  showing  (from  left  to  right)  bearing  habits  of  filbert,  chestnut 
and  walnut.  In  filbert  and  walnut  B  equals  pistillate  flower  buds,  C  equals  staminate 
flower  buds;  M  equals  male  catkins. 


they  may  have  resting  buds  which  give  rise  to  vegetative  or  pistillate 
flower-bearing  shoots  the  following  year. 

The  cashew  nut  {Anacardium)  and  the  Brazil  nut  (Bertholletia)  also  bear 
terminally  on  shoots  from  lateral  buds. 

In  the  cherimoya,  pond-apple,  sour-sop,  sugar-apple  and  various  other 
Anonaceous  fruits  the  fruit  buds  are  borne  laterally  and  the  inflorescences 
terminally,  with  the  growth  of  the  flowering  shoots  proceeding  much  as  in  the 
grape.  Here  the  flowers  and  fruits  appear  to  be  between  nodes,  or  extra-axillary. 
Not  infrequently  they  develop  on  short  spur-like  branches. 

In  the  blueberries  the  inflorescences  develop  both  terminally  and  in 
the  axils  of  leaves  on  new  shoots  springing  from  lateral  buds.  This  bear- 
ing habit  is  a  combination  of  the  typical  concHtions  found  in  Groups  V 
and  VI  as  here  classified.  Ordinarily  there  are  no  true  terminal  buds  in 
this  group  but  if  terminal  buds  are  formed  they  are  usuallj^  fruit  buds. 
In  Vaccinimn  atrococcum  the  flowering  shoot  has  no  foliage.  Fruit  bud 
differentiation  apparently  takes  place  in  late  fall  in  the  axils  of  leaves 
near  the  end  of  the  shoot. 


404  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

The  European  cranberry  {Vaccinium  oxycoccus),  litchi  {Nephelium  litchi) 
and  sea-grape  {Coccoloba  iwifera)  have  similar  bearing  habits. 

Group  VI. — Fruit  buds  borne  laterall}^  (or  pseudoterminally),  unfold- 
ing to  produce  leafy  shoots  with  flower  clusters  in  the  leaf  axils. 

In  the  persimmon  any  lateral  bud  and  not  infrequently  adventitious 
or  dormant  buds  on  2-year-old  or  older  wood,  may  become  a  fruit  bud. 
The  following  year  these  unfold  and  form  leafy  shoots  with  solitary 
pistillate  or  with  clusters  of  staminate  flowers  in  the  axils  of  the  more 
basal  leaves.  The  male  and  female  flowers  may  be  borne  on  the  same 
tree  or  on  different  trees. 

The  mulberry  has  a  similar  bearing  habit,  except  that  both  pistillate 
and  staminate  flowers  are  usually  borne  on  the  same  flowering  shoot. 
The  male  flowers  are  formed  in  the  axils  of  the  more  basal  leaves  and  the 
pistillate  flowers  in  the  axils  of  higher  leaves. 

In  the  American  cranberry  {Vaccinium  macrocar'pon)  the  flowering 
shoots  arise  from  lateral  buds  on  the  creeping  vegetative  branches.  The 
flowers  are  borne  singly  in  the  leaf  axils. 

The  chestnut,  chinquapin,  oak  and  beech  have  very  similar  bearing 
habits  (see  Fig.  47).  The  pseudoterminal  or  more  apical  lateral 
buds,  when  they  differentiate  flower  parts,  give  rise  to  shoots  in  the  axils 
of  the  leaves.  Male  catkins  appear  in  the  lower  axils  and  female,  or 
mixed  male  and  female,  clusters  above  them.  Sometimes  dwarf  shoots 
arise  from  the  basal  buds  in  the  chestnut  and  produce  male  catkins  only 
in  the  leaf  axils.  True  terminal  buds  are  sometimes  formed  in  the  oak 
and  beech  and  these  may  be  fruit  buds.  In  the  beech  there  are  short 
spur-like  growths  which  have  no  lateral  buds  except  a  single  pseudo- 
terminal  bud.     This  is  never  a  flower  bud. 

The  fig  bears  lateral  fruit  buds.  Its  pseudoterminal  bud,  which  is  usually 
larger  than  the  others,  is  generally  vegetative.  Frequently  more  than  one 
bud  is  formed  in  a  leaf  axil  and  they  appear  in  pairs,  side  by  side.  The  fruits  are 
formed  singly  in  the  leaf  axils.  The  fig  can  bear  three  (or  more,  according  to 
some  authorities)  distinct  crops  in  a  year. 

In  the  avocado  the  lateral  flower  buds  give  rise  to  flowering  shoots  in  which 
the  inflorescences  are  in  the  axils  of  the  more  basal  leaves. 

The  pistachio  {Pistacia  vera)  and  star  apple  {Chrijsophyllum)  have  a  similar 
bearing  habit  and  the  olive,  which  has  been  mentioned  as  belonging  in  Group 
III,  might  as  readily  be  included  here,  since  it  produces  lateral  as  well  as  terminal 
flower  buds. 

In  the  jujube  {Zizyphus  jujube)  several  flowering  branches  may  arise  at  a 
single  node.  Solitary  flowers  are  borne  in  the  leaf  axils  of  these  branches.  After 
the  ripening  of  the  fruit  the  leaves  and  fruit  fall  off  and  finally  the  entire  branch 
falls.  Buds  for  the  following  crop  are  differentiated  on  strictly  vegetative 
branches.  There  is  thus  a  definite  dimorphism  of  branches  in  this  species,  the 
fruiting  branches  being  deciduous  and  not  forming  a  part  of  the  permanent 
framework  of  the  tree. 


GROWING  AND  FRUITING  HABITS  405 

Group  VII. — Fruit  buds  borne  both  terminally  and  laterally,  inflo- 
rescences generally  terminal.  The  fruits  that  are  discussed  here  might 
be  included  with  those  of  Groups  II  and  IV  for  they  represent  a  combi- 
nation of  those  two  fruiting  habits,  but  for  convenience  they  are  con- 
sidered separatel.y. 

In  the  walnut,  hickory  and  pecan  the  terminal  bud  may  give  rise  to 
a  short  leafy  shoot  ending  in  a  female  inflorescence  (see  Figure  48).  The 
male  flowers  are  borne  on  leafless  inflorescences  arising  from  lateral 
buds  not  far  below  the  terminal.  In  the  walnut  there  are  two  superposed 
buds  in  each  leaf  axil,  the  upper  being  usually  the  first  to  open.  At  a 
single  node  two  male  inflorescences  may  appear  simultaneously  from  the 
two  buds,  or  a  leafy  shoot  may  come  from  the  upper  and  an  inflorescence 
from  the  lower.  In  the  hickory  the  male  catkins  are  sometimes  borne 
in  the  axils  of  the  basal  leaves  on  the  terminal  shoot,  resulting  in  the  pro- 
duction of  male  and  female  flowers  on  the  same  shoot. 

Group  VIII. — Fruit  buds  adventitious.  Since  adventitious  fruit 
buds  are  necessarily  lateral,  the  plants  included  here  might  readily  be 
classed  with  those  of  Groups  IV,  V  or  VI.  However,  this  bearing  habit 
is  more  or  less  distinct  and  these  fruits  may  well  be  placed  in  a  separate 
class. 

The  jaboticaba  and  cambuca  form  adventitious  flower  buds  on  their  trunks, 
main  and  smaller  limbs  and  even  on  their  exposed  roots.  These  produce  no 
leaves  when  they  open. 

The  cacao  bears  in  the  same  way,  though  the  flower  buds  appear  first  on  the 
trunk  and  as  the  trees  grow  older,  on  the  whorled  branches. 

The  coffee  produces  fruiting  branches  from  adventitious  buds  at  the  nodes. 
The  upper  bud  becomes  a  horizontal  fruit-bearing  branch,  the  lower  an  upright 
vegetative  shoot. 

Group  IX. — There  is  another  group  of  plants  which  have  fruit  buds 
in  the  axils  of  the  leaves  and  in  which  these  buds  unfold  and  develop 
their  flowers  and  fruits  very  soon  after  the  flower  parts  are  differentiated. 
However,  it  is  not  possible  to  draw  a  clear  line  between  this  fruiting 
habit  and  that  described  for  Group  IV. 

This  group  includes  the  passion  fruit  (Passiflora),  the  papaya  (Carica  papaya) 
and  many  others  with  a  more  or  less  herbaceous  type  of  growth.  In  culture, 
as  well  as  in  growing  and  fruiting  habits,  these  plants  resemble  certain  vegetables 
more  closely  than  deciduous  fruits. 

The  Relation  of  Fruiting  Habit  to  Alternate  Bearing.— Terminal 
fruit  bud  formation  often  has  been  regarded  as  an  explanation  of  the 
alternate  bearing  frequently  occurring  in  species  or  varieties  with 
this  fruiting  habit.  However,  not  all  the  terminal  buds  on  shoots  and 
spurs  of  plants  with  a  terminal-fruit-bud-bearing  habit  develop  into 
fruit  buds  at  one  time.     Many  are  leaf  buds  and  unfold  Icafv  non- 


406  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

flowering  shoots  or  spurs.  Fruit  bud  differentiation  depends  on 
nutritive  conditions  in  and  about  the  terminal  bud  at  such  time  or  times 
when  differentiation  can  take  place.  Terminal  bearing  involves  a  definite 
limitation  to  shoot  or  spur  extension  in  a  straight  line.  New  vegetative 
extension  must  be  from  lateral  buds  if  all  terminals  form  fruit  buds  in 
one  season,  but  this  seldom  occurs  and  those  buds  that  do  not  become 
fruit  buds  one  year  may  therefore  become  differentiated  into  fruit  buds 
the  next  season.  In  this  way  regular  annual  bearing  is  possible  if  nutri- 
tive conditions  within  the  plant  remain  such  that  fruit  bud  differentia- 
tion can  occur  each  year.  Even  if  all  terminals  were  to  differentiate 
fruit  buds  one  season  and  to  flower  and  fruit  the  next,  there  would  still 
be  opportunity  for  the  formation  of  another  set  of  fruit  buds  terminally 
on  the  new  shoots  or  new  spurs.  Therefore  regular  annual  bearing  would 
still  be  possible  provided  nutritive  conditions  were  favorable.  The 
terminal  fruiting  habit  does  not  in  itself  lead  to  alternate  bearing  except 
in  the  event  that  practically  every  terminal  forms  a  fruit  bud  one  season 
and  sets  fruit  the  next  while  at  the  same  time  growing  conditions  this 
second  season  prevent  fruit  bud  differentiation  on  the  new  shoots  or 
spurs  developed  from  lateral  buds.  When  this  extreme  is  encountered 
it  should  be  handled  as  a  problem  in  nutritive  conditions  to  be  corrected 
by  the  control  of  environmental  factors.  In  other  words,  though  many 
varieties  of  plants  which  bear  fruit  buds  terminally  are  much  inclined 
to  alternate  bearing,  that  tendency  is  not  a  necessary  product  or  accom- 
paniment of  terminal  fruit  bud  formation. 

Obviously  the  production  of  fruit  buds  laterally  on  either  spurs  or 
shoots  makes  every  provision  for  regular  annual  bearing,  not  only  of 
the  plant  as  a  whole,  but  of  the  individual  part,  if  conditions  within  the 
plant  are  favorable  for  fruit  bud  differentiation. 

Regularity  of  bearing,  therefore,  is  a  cultural  problem,  to  be  dealt 
with  by  influencing  nutritive  conditions.  Attention  is  given  to  this 
phase  of  the  question  in  the  section  on  Nutrition. 

Possible  Causes  of  Different  Bearing  Habits. — Knowledge  of  bearing 
habits  is  decidedly  fragmentary  and  little  is  known  concerning  the  factors 
which  may  control  it  or  influence  it  in  any  way.  However,  it  is  known 
that  the  apple  with  its  characteristic  terminal  fruit  bearing  habit  stores 
the  bulk  of  its  starch  in  the  pith  while  the  peach  with  its  characteristic 
lateral  fruit  bearing  habit  stores  the  bulk  of  its  starch  in  the  leaf  gaps. 
Since  carbohydrate,  and  particularly  starch,  accumulation  is  so  closely 
associated  with  fruit  bud  differentiation,  at  least  in  the  apple,  it  is 
possible  that  anatomical  structure  may  have  much  to  do  with  the  region 
of  starch  storage  and  that  this  in  its  turn  may  be  an  important  factor 
determining  the  bearing  habit. 

Summary. — The  general  purpose  of  all  pruning  is  to  increase  yields, 
improve  grades  and  reduce   production   costs.     These  objects  may  be 


GROWING  AND  FRUITING  HABITS  407 

attained  either  through  modifying  the  form  or  through  influencing  the 
functioning  of  the  tree  as  a  whole  or  of  its  individual  parts.  Pruning 
for  form  is  essentially  training.  Training  seeks  directly  to  secure  the 
distribution  of  the  fruit  bearing  parts  that  is  most  advantageous  for 
economy  of  production,  disease  and  insect  control,  for  minimum  loss 
from  breaking  of  limbs  and  for  proper  coloration.  These  ends  are  fur- 
thered by  (1)  heading  the  tree  properly,  (2)  providing  a  reasonable 
number  of  well-spaced  scaffold  limbs,  (3)  preventing  the  formation  of 
weak  crotches,  and  (4)  keeping  the  tops  of  the  trees  from  growing  too 
high  or  spreading  too  far.  Pursuant  to  these  aims  the  plants  are  generally 
trained  in  one  or  another  of  several'  standard  shapes.  Thus  training 
results  in  a  certain  degree  of  uniformity  of  appearance  in  the  orchard. 
The  bearing  habits  of  most  species  and  varieties  are  fairly  well  fixed, 
though  they  are  subject  to  some  modification  by  pruning  and  other 
cultural  treatment.  Fruit  buds  are  differentiated  either  terminally  or 
laterally  and  when  they  open  they  may  give  rise  to  (1)  leafless  flower 
clusters,  (2)  leafy  growths  with  terminal  flower  clusters,  or  (3)  leafy 
growths  with  lateral  flower  clusters.  There  are  thus  six  distinct  bearing 
habits  and  in  addition  a  number  of  combinations  between  these  types. 
The  more  common  fruits  are  classified  in  respect  to  their  bearing  habits. 
Alternate  bearing  is  not  a  necessary  product  of  any  type  of  bearing.  If 
nutritive  conditions  within  the  tree  are  favorable  fruit  buds  may  be 
formed  every  year.  Consequently  alternate  bearing  is  a  problem  in 
nutrition.  Different  bearing  habits  are  probably  associated  with  differ- 
ent methods  or  places  of  food  storage. 


CHAPTER  XXII 
PRUNING— THE  AMOUNT  OR  SEVERITY 

Pruning  can  vary  in  three  major  respects  and  in  three  only.  It  can 
vary:  (1)  in  amount  or  severity,  (2)  in  kind  or  distribution  and  (3)  in  the 
season  at  which  it  is  done.  Characteristic  responses  by  the  plant  are 
to  be  expected  not  only  as  the  pruning  varies  in  any  of  these  three  respects 
but  according  to  fruiting  habit  and  as  the  plant  itself  varies  in  age,  vigor 
and  nutritive  condition.  These  three  major  aspects  of  pruning  are  dis- 
cussed in  the  order  in  which  they  have  been  mentioned. 

A  search  through  horticultural  literature  reveals  a  great  diversity  of 
opinion  as  to  the  influence  of  varying  amounts  of  pruning  on  growth  and 
productiveness.  Some  have  considered  heavy  pruning  a  great  stimulant 
to  vegetate  growth  especially,  though  perhaps  having  the  opposite  effect 
on  fruit  production.  This  idea  is  reflected  in  the  phrase  "prune  in  the 
winter  for  wood."  Others  have  regarded  pruning  of  any  kind  and  more 
particularly,  pruning  in  any  amount,  as  a  harmful  practice  because  it  has 
been  thought  to  check  growth.  Most  of  these  partly  accepted  ideas  have 
been  based  upon  theoretical  considerations  or  field  observations,  of  which 
some  have  been  sound  and  accurate  but  many  have  been  either  fallacious 
or  inaccurate  or  have  failed  to  consider  other  important  facts.  Not  until 
comparatively  recent  years  have  exact  and  pertinent  experimental  data 
been  available. 

Influence  on  Size  of  Tree. — Bedford  and  Pickering^  were  among  the 
first  to  make  a  careful  study  of  the  different  effects  of  various  amounts  of 
dormant  season  pruning  on  the  apple.  Table  1  shows  the  mean  tree 
size  and  weight  for  all  varieties  studied  and  given  different  pruning  treat- 
ments covering  a  period  of  ten  years.  The  figures  for  tree  size  take  into 
consideration  spread  and  height  and  trunk  circumference.  Clearly  these 
show  that  the  unpruned  tree  increases  in  size  and  weight  more  rapidly 

Table    1. — Influence    of   Amount   of   Pruning    on   Tree    Size  in  the  Apple 

(After  Bedford  and  Pickering*) 

Very  Little  or  no  Pruning  Moderate  Pruning        Hard  Pruning 

Tree  size  relative.  .  106  100  82 

Tree  weight  relativel20  100  84 

than  the  pruned  tree  and  that  the  heavier  the  pruning  the  more  pro- 
nounced is  the  check  upon  growth.  In  commenting  on  the  somewhat 
greater  influence  of  pruning  on  weight  than  on  size  revealed  by  the  figures 
in  the  table  Bedford  and  Pickering  remark,  ''This  increase  in  weight 
must  be  due  to  an  increase  in  weight  of  the  stem  and  main  branches,  for  it 

408 


PRUNING— THE  AMOUNT  OR  SEVERITY 


409 


cannot  be  accounted  for  merely  by  the  weight  of  wood  removed  during 
pruning:  the  prunings  would,  on  an  average,  have  amounted  to  27 
pounds  per  tree  during  the  ten  years  in  the  case  of  the  moderately  pruned 
trees,  whereas  these  trees  at  the  end  of  this  time  showed  a  deficit  of  49 
pounds  as  compared  with  the  unpruned  ones."  Gardner'^  in  Oregon  and 
Alderman  and  Auchter^  in  West  Virginia  (see  Table  2),  both  working 
with  young  apple  trees,  obtained  results  leading  to  the  same  conclusions. 
The  unpruned  tree  increases  in  size  more  rapidly  than  the  moderately 
or  heavily  pruned  tree,  not  because  it  produces  more  new  shoot  growth 
each  year,  but  because  it  losses  none  by  pruning.  Tufts, ^^  in  California, 
studying  the  influence  of  varying  amounts  of  pruning  on  newly  set 
apricots,  sweet  cherries,  peaches,  pears  and  European  and  Japanese 
plums  found,  in  every  instance,  less  rapid  increases  in  trunk  circumference 
with  each  increase  in  the  severity  of  the  pruning  (see  Table  3).  Since 
he  found  correlation  coefficients  ranging  from  0.83  to  0.92  for  trunk  cir- 
cumferences and  weights  of  top  and  coefficients  ranging  from  0.76  to 
0.84  for  trunk  circumferences  and  weights  of  root,  depending  on  the 
species,  it  is  evident  that  trunk  circumferences  may  be  taken,  other 
things  equal,  as  fairly  accurate  indices  to  tree  size.  Consequently  his 
data,  together  with  those  of  the  investigators  already  cited,  are  evidence 
that,  in  general,  pruning  results  in  a  check  to  increase  in  size.  At  least 
it  may  be  considered  established  that  this  holds  for  deciduous  tree  fruits. 


Table  2. 


-Influence  of  Amount  of  Pruning  on  Size  of  Young  Apple  Trees 
(After  Alderman  and  Auchter'^) 


Variety 


Type  of 
pruning 


Number 
of  trees 


Height 
(in  feet) 


Spread 
(in  feet) 


Stayman 

Stayman 

Stayman 

Rome 

Rome 

Rome 

Gravenstein 

Gravenstein 

Gravenstein 

Stark 

Stark 

York,  Grimes  and  Rome 
York,  Grimes  and  Rome 
York,  Grimes  and  Rome 


Heavy 

Moderate 

Light 

Heavj' 

Moderate 

Light 

Heavy 

Moderate 

Light 

Heavy 

Light 

Heavy 

Moderate 

Light 


7.32 
7.89 
9.50 

7.45 
8.18 
9.16 

7.43 
6.83 
8.94 

7.57 
10.79 

9.55 
9.73 
10.50 


5.29 
5.52 
5.75 

3.68 
4.17 
4.23 

4.05 
4.19 
4.34 

5.17 
6.85 

4.83 
6.17 
7  10 


410 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Table  3. — Increase  in  Trunk  Circumference  under  Varying  Pruning 

Treatments 
{After  Tufts''') 


Kind  of  fruit 


Pruned 

severely 

(centimeters) 


Pruned  • 
moderately 
(centimeters) 


Pruned 

lightly 

(centimeters) 


Apricot  (Royal) .  .  . 
Cherry  (Napoleon) 
Peach  (Elberta) .  .  . 
Pear  (Bartlett) . . .  . 
Plum  (Climax) .  .  .  . 

Plum  (Pond) 

Prune  (French) ... 

Average 


11.7 
10.0 
12.0 

8.7 
6.3 
7.2 
6.2 

8.9 


12.6 
11.2 
16.9 
9.1 
10.4 
8.8 
7.1 

10.9 


15.3 

12.3 

19.4 

9.7 

11.3 

9.4 

8.4 

12.3 


Amount  and  Character  of  New  Shoot  Growth. — The  framework  of  the 
tree  is  developed  from  its  shoots  of  the  preceding  or  earlier  years.  Since 
the  general  influence  of  pruning  is  to  check  increase  in  size,  it  might  be 
reasoned  that  it  results  in  a  corresponding  decrease  in  the  amount  of  new 
shoot  growth  produced  each  year.  On  the  other  hand  it  is  possible  that 
the  check  to  increase  in  size  might  be  due  largely,  or  even  entirely,  to  the 
annual  removal  of  wood.  Experimental  data  on  this  question  were 
obtained  by  Bedford  and  Pickering.^  They  selected  a  number  of  shoots 
in  a  tree,  all  as  nearly  as  possible  of  uniform  length  (about  36  inches)  and 
thickness.  Some  were  pruned  back  to  a  length  of  6  inches,  some  to 
12  inches,  some  to  24  and  some  had  only  their  terminal  buds  removed. 
Table  4  shows  the  relative  numbers,  lengths  and  weights  of  the  new  side 
shoots  that  were  formed  and  also  the  influence  of  these  treatments  on  the 
parent  branch.  Heavy  pruning  back  resulted  in  fewer  side  shoots  with 
less  total  length  and  less  weight  than  lighter  pruning  or  than  none  at 
all.  The  greatest  decrease  was  in  the  number  of  new  shoots,  from 
which  it  may  be  inferred  that  individually  these  shoots  were  somewhat 
longer  and  stronger  than  those  on  the  lighter  pruned  limbs.     The  differ- 

Table  4. — Effects  of  Pruning  Back  Individual  Shoots    Varying  Amounts 
(After  Bedford  and  Pickering'^) 

Length  of  shoot  after  pruning,  in  inches 6         12  24  36 

Weight  of  original  shoot  and  laterals  (relative) 100  179  310  562 

Thickening  of  the  original  shoot  (relative) 100  114  117  129 

New  shoots  formed: 

Number  (relative) 100  116  198  292 

Length  (relative) 100  113  145  183 

Weight  (relative)    100  108  123  142 

ence  in  weight  of  old  wood  after  a  year's  growth  is  particularly  striking, 
the  unpruned  trees  having  over  five  times  the  amount  of  those  pruned 


PRUNING— THE  AMOUNT  OR  SEVERITY 


411 


heavily.  These  same  investigators  found,  however,  that  in  mature 
trees  that  had  been  bearing  for  a  number  of  years  heavy  pruning  resulted 
in  almost  twice  as  much  new  shoot  growth  as  was  produced  by  unpruned 
trees. 

On  the  other  hand  Blake  and  Connors,^  in  New  Jersey,  found  that 
pruned  peach  trees  produced  in  the  first  year  somewhat  more  new  shoot 
growth  than  unpruned  trees.  The  average  for  the  latter  in  their  Vineland 
experiment  was  695  inches  and  for  the  pruned  trees  (all  treatments) 
753  inches.  In  West  Virginia,  Alderman  and  Auchter^  report  that  heavy 
pruning  of  the  apple  resulted  in  somewhat  greater  new  shoot  growth  for 
the  first  2  or  3  years,  but  that  greater  shoot  development  accompanied 
lighter  pruning  as  the  tree  became  older  (see  Table  5).  Gardner^^ 
in  Oregon,  likewise  working  with  young  apple  trees,  found  that  different 

T.iBLE   5. — Effect  of  Light  and   Heavy   Pruning   on  New  Shoot  Growth  in 
Apples  of  Different  Ages 
(After  Alderman  and  Auchter^) 


Pruned  heavily 

Pruned  lightly 

Season 

Average  total 
length,  feet 

Average  total 
removed,  feet 

Average  total 
length,  feet 

Average  total 
removed,  feet 

pruning  (feet) 

1911 

4.41 

3.30 

5.58 

3.44 

1912 

16.25 

12.91 

15.51 

4.78 

-0.74 

1913 

41.53 

33.16 

34.33 

13.89 

-7.20 

1914 

84.08 

49.17 

99.39 

22.12 

15.31 

1915 

161.74 

224.89 

63.15 

varieties  respond  in  a  quite  dissimilar  manner  to  pruning  of  the  same 
severity.  His  data,  some  of  which  are  summarized  in  Table  6,  show  that 
lightly  or  moderately  pruned  Grimes  produced  more  shoot  growth 
annually  than  unpruned  trees,  but  those  heavily  pruned  produced  dis- 
tinctly less  than  the  check  trees.  On  the  other  hand  the  heavily  pruned 
Romes  produced  more  shoot  growth  annually  than  those  pruned  moder- 
ately or  not  at  all,  while  on  the  whole  the  severity  of  annual  j^runing 
seemed  to  make  but  little  difference  in  the  amount  of  new  shoot  growth 
in  Gano  and  Esopus.  At  first  these  data  may  seem  so  contradictory 
that  no  conclusion  or  interpretation  is  possible.  However,  attention 
may  be  called  to  the  great  variations  shown  by  young  apple  trees  of 
different  varieties  in  their  growing  habits  and  to  the  change  in  these 
differences  with  age.  Thus  there  is  a  great  dissimilarity  between  young 
trees  of  Rome  and  Grimes  in  the  number  of  spurs  and  the  peach  usually 
produces  no  true  spurs.  When  these  peculiarities  of  age  and  variety  are 
considered  along  with  the  data  that  follow  on  the  influence  of  various 
pruning  treatments  on  fruit  spur  and  fruit  bud  production  the  contradic- 
tions that  have  been  noted  do  not  appear  so  puzzling. 


412 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Table  6. — Effect  of  Light  and  Heavy   Pruning   on   New  Shoot  Growth  in 

Young  Apples  op  Different  Varieties 

(After  Gardner^'^) 


Number  of 
trees  aver- 
aged 


Severity  of 
annual  prun- 
ing,   per 
cent. 


Average  1914 

shoot  growth, 

centimeters 


Average  1915 

shoot  growth, 

centimeters 


Average  1916 

shoot  growth, 

centimeters 


Average 

number  fruit 

spurs  in  fall 

of  1916 


Grime.s. 
Grimes. 
Grimes. 
Grimes. 
Gano. . 
Gano. . 
Rome. . 
Rome . . 
Rome.  . 
Esopus. 
Esopus. 


none 
0-25 
26-50 
51-75 
26-50 
51-75 
none 
26-50 
51-75 
none 
46-76 


492 
675 
714 
378 
456 
561 
629 
508 
845 
583 
453 


1762 
2251 
2401 
1339 
2493 
2464 
2051 
1973 
2541 
2121 
1736 


3852 
4713 
4913 
2818 
5435 
5459 
3520 
3634 
4630 
2287 
3077 


402 
457 
341 
116 
158 
111 
142 
34 
31 
505 
134 


In  recapitulation  it  may  be  said  that  different  species  and  varieties 
show  great  variations  in  their  response  by  new  shoot  production  to  prun- 
ings  of  like  severity.  These  differences  are  due  primarily  to  growing 
and  fruiting  habits  and  secondarily  to  age,  vigor  and  nutritive  conditions, 
as  well  as  to  environmental  conditions  with  which  they  may  happen  to  be 
associated  at  the  time. 

Leaf  Surface  and  Root  System. — Any  practice  that  would  effect  a 
reduction  in  the  amount  of  new  shoot  growth  and  perhaps  of  spurs  as 
well,  would  be  expected  to  result  in  a  corresponding  decrease  in  leaf 
area  and  in  root  development.  Chandler's^ ^  investigations  of  the  rela- 
tion of  certain  pruning  practices  to  subsequent  root  development  show 
this  reduction.     Some  of  his  data  are  summarized  in  Tables  7  and  8. 


Table  7. — Influence  of   Varying  Amounts  of  Pruning  on  Subsequent  Leaf 

AND  Root  Development 

{After  Chandler'') 


Treatment 

Number  of 
trees 

Average  leaf 
surface  be- 
fore pruning, 

May  23, 

1918  (square 

inches) 

Average  leaf 
surface  after 

1918  (square 
inches) 

Average  leaf 
surface, 
Sept.    17, 

1918  (square 
inches) 

Average  root 

weight 

May  19, 

1919  (grams) 

Average  top 
weight. 
May   19, 
1919     in- 
cluding prun- 
ings  (grams) 

Unpruned 

Little  pruning .  . 
Much  pruning . . 

41 
33 
39 

756.48 
819.14 
775.70 

756.48 
470 . 27 
291.61 

1737.94 
1219.80 
895.96 

208.5 
166.9 
126.3 

684.0 
558.3 
494.3 

In  commenting  on  the  data  presented  in  Table  8,  Chandler"  says: 

"It  will  be  seen  that  in  all  cases  the  leaf  surface  has  been  rather  markedly 
reduced.     On  the  other  hand  except  in  case  of  the  summer-pruned  trees,  when 


PRUNING— THE  AMOUNT  OR  SEVERITY 


413 


Table  8. — Effect  of  Pruning  on  Leaf  Surface  and  Top  and  Root  Growth  of 

Peach  Trees  4  Years  Old  at  Beginning  of  Experiment 

(After  Chandler^') 


Average 

leaf  sur- 

Average  leaf  sur- 

face in  1916 

face  in   1917 

Tree. 

Root 

Treatment 

June, 

Sep- 

June, 

Sep- 

weight. 

weight. 

square 
inches 

tcmber, 
square 
inches 

square 
inches 

tember, 
square 
inches 

pounds 

pounds 

pounds 

Elberta: 

Pruned  1910  and  1917 

14,239 

80,659 

31,209 

59,579 

90.3 

11G.4 

27.4 

Unpruned 

24,771 

97 , 8oO 

98,169 

116,344 

116.3 

110.3 

37.3 

Crawford  Early: 

Pruned   summer    1910,     spring 

1917 

2,202 

50,034 

18,904 

68,070 

75.8 

97.4 

20.9 

Unpruned 

17,886 

85,721 

74,389 

142,920 

111.9 

111.9 

34.6 

Pruned  spring  1917 

40,681 

79 , 563 

120.  3 

134.7 

34.9 

114,516 

144,911 

131.7 

131.7 

the  weight  of  the  prunings  has  been  added  to  that  of  tlie  tree,  the  t(jtal  weight 
of  pruned  and  unpruned  trees  is  practically  the  same.  The  root  growth,  how- 
ever, has  been  greatly  reduced.  When  it  is  considered  that  this  reduction  in 
growth  has  occurred  during  the  last  2  years  of  the  6  years  during  which  the  trees 
have  been  in  the  orchard,  it  will  be  realized  how  striking  the  reduction  is.  Thus 
if  at  the  beginning  of  1916  the  roots  weighed  15  pounds,  then  the  root  growth 
on  the  unpruned  trees  since  that  time  has  been  nearly  twice  that  on  the  pruned 
tree.  Unfortunately  we  have  no  records  as  to  the  root  weight  of  trees  4  years 
old,  but  it  must  have  been  10  pounds  or  more,  since  by  records  that  we  have  the 
tops  would  then  have  weighed  from  30  to  35  pounds.  If  the  root  weight  at  the 
beginning  was  10  pounds,  then  the  root  growth  in  the  pruned  trees  since  that 
time  has  been  but  65  per  cent,  of  that  made  by  the  unpruned  trees." 

In  effect  the  influence  of  a  heavy  top  pruning  on  the  subsequent 
development  of  the  tree  is  more  or  less  comparable  to  that  of  a  root 
pruning. 

Presumably,  pruning  practices  which  do  not  reduce  top  growth  in 
trees  of  other  kinds  or  of  greater  age  than  those  studied  would  not  have 
such  an  influence  on  root  growth;  exact  data,  however,  are  lacking.  It 
is  significant,  nevertheless,  that  in  young  trees  pruning  of  the  top  has 
been  found  greatly  to  influence  the  extent  of  root  development  the 
following  season.  This  suggests  one  of  the  indirect  ways  through  which 
pruning  one  season  may  influence  growth  and  development  2  or  3  years 
later. 

Influence  on  Fruit  Spur  and  Fruit-bud  Formation. — In  Table  6 
are  presented  data  on  the  influence  of  varying  amounts  of  pruning  on 
fruit  spur  formation  in  young  apple  trees.  The  less  the  pruning  the  larger 
is  the  number  of  fruit  spurs  formed.     With  very  severe  pruning  there  is  a 


414  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

great  reduction,  the  checking  influence  differing  greatly  with  the  variety, 
however.  Varieties  Hke  Esopus  and  Grimes,  that  are  much  inclined  to 
develop  spurs  at  an  early  age,  show  a  relatively  greater  check  in  this 
respect  than  those  like  Rome  and  Gano  that  as  young  trees  produce 
comparatively  few  spurs.  In  any  case,  however,  pruning  tends  to  reduce 
their  number.  Data  are  presented  showing  also  that  severe  pruning  acts 
in  a  similar  manner  in  decreasing  the  numbers  of  fruit  buds  that  form 
on  the  spurs.  ^^  Similar  data  on  fruit  bud  formation  in  young  apple 
trees  have  been  obtained  in  West  Virginia^  and  in  England.'*  The  ratio 
of  flower  clusters  for  the  years  1909-1914  obtained  by  the  English 
investigators  in  one  of  their  experiments  was  52  for  hard  pruning,  100 
for  moderate  pruning  and  180  for  no  pruning.  There  were  corresponding 
differences  in  total  yield.  All  these  investigators  show  that  heavily 
pruned  trees  may  be  expected  to  come  into  bearing  more  slowly  than 
those  pruned  moderately,  lightly  or  not  at  all. 

On  the  other  hand,  heavy  pruning  does  not  always  result  in  decreased 
yields.  Data  obtained  in  an  experiment  with  Arkansas  and  York 
Imperial  apple  trees  that  had  been  bearing  for  a  number  of  years  and 
were  somewhat  lacking  in  vigor,  summarized  in  Table  9,  show  steady 
increments  in  yield  with  each  increase  in  the  severity  of  the  pruning.  ^ 

Table  9. — Influence  of  Pruning  on  Yields  in  a  Declining  Apple  Orchard 
{After  Alderman  and  Auchter"^) 


AFKaiisas,   iwit-ivdo  i  orK,      lyit     crop 

crops  (bushels  per  tree)        (bushels  per  tree) 


Arkansas,  1914-1915 


York,     1914     crop 


Heavy  pruning .  . .  . 
Moderate  pruning . 
Light  pruning 


14.02 

11.94 

9.15 


The  heavy  pruning  must  have  had  the  effect  of  reducing  somewhat  the 
total  number  of  fruit  spurs,  at  least  in  comparison  with  the  trees  pruned 
more  lightly.  Consequently  the  increased  yields  must  have  been  due 
either  to  the  formation  of  a  larger  number  of  fruit  buds  or  to  the  better 
setting  of  the  blossoms.  This  is  an  influence  not  unlike  that  already 
pointed  out  as  very  frequently  attending  the  judicious  use  of  nitrogenous 
fertihzers. 

Influence  on  Leaf  Area  and  Fruit  Size. — In  Table  10  are  presented  data 
on  the  influence  of  varying  amounts  of  pruning  on  average  size  of  leaf 
and  total  leaf  area  in  apple  trees.  Not  only  are  the  individual  leaves  of 
the  heavily  pruned  trees  larger  than  those  of  the  unpruned  or  lightly 
pruned  trees,  but  there  are  more  of  them.  Consequently  such  trees 
have  a  materially  increased  leaf  surface.  This  in  turn  creates  a  greater 
requirement  for  nutrients  and  for  moisture;  if  this  requirement  is  met,  an 
increased  production  of  elaborated  foods  may  be  expected. 


PRUNING— THE  AMOUNT  OR  SEVERITY 


415 


Table  10. — Influence  of  Pruning  on  Leaf  Size  Area 
(After  Alderman  and  Auchter^) 


I'uf    area    (s<iuare 
inches) 


Lupton 
orchard 


Grimes 
orchard 


Total    leaf    area    per    tree 
(.square    feet) 


Lupton  Grimes 

orchard  orchard 


Heavy  pruning. .  . 
Moderate  pruning 
Light  pruning.  .  .  . 


2.77 
2.37 
2.10 


4.99 
4.18 
3.52 


610.8 
432.2 
418.7 


1143.8 
911.5 
659.6 


The  decrease  in  size  of  fruit  recorded  by  Bedford  and  Pickering* 
as  accompanying  severe  pruning  probably  is  explained  by  the  increased 
leaf  area  of  the  trees  and  the  consequently  greater  requirement  of  this 
foliage  for  water — a  requirement  that  under  the  conditions  of  the  experi- 
ment the  roots  were  unable  to  supply.  Experience  and  observation 
generally  indicate  that  pruning  does  not  decrease  size  of  fruit.  As 
a  matter  of  fact  it  often  has  the  opposite  effect.  Perhaps  this  tendency 
is  most  clearly  shown  in  such  fruits  as  the  raspberry,  blackberry  and  grape 
which  in  the  absence  of  pruning  are  inclined  to  set  more  fruit  than  they 
can  mature  properly,  especially  when  supporting  the  large  amount  of 
barren  wood  which  unpruned  plants  of  these  species  characteristically 
bear.  Within  certain  rather  wide  limits  the  general  influence  of  pruning 
is  to  reduce,  through  the  removal  of  actual  or  potential  bearing  wood, 
the  amount  of  fruit  that  can  set.  It  tends  also  to  enlarge  leaf  area 
and  thus,  though  its  effects  are  concentrating,  it  at  the  same  time  increases 
the  requirement  for  nutrients  and  moisture.  If  these  are  available  in  ample 
quantities  pruning  may  result  in  an  increase  in  size  of  fruit;  if  they  are 
lacking  it  may  result  in  a  reduction.  Though  the  general  tendency  of 
pruning,  as  of  fertilization,  is  to  increase  the  size  of  the  fruit,  its  influence 
in  this  regard  is  not  direct.  Nevertheless  it  is  one  of  the  most  important 
means  at  the  grower's  disposal  for  this  purpose.  This  is  particularly 
true  for  those  species  or  varieties  with  which  thinning  of  the  fruit  is 
impracticable. 

Pruning  as  a  Cause  of  Abnormal  Structures. — In  the  sections  on 
Water  Relations  and  Nutrition  attention  is  directed  to  certain  patho- 
logical conditions  that  may  result  from  extremes  of  moisture  or  from  an 
unbalanced  nutrient  supply.  Pruning  may  disturb  both  the  water  and 
food  relations  of  the  plant;  hence  certain  pathological  conditions  may 
follow,  particularly  from  heavy  pruning.  Daniel,'*  who  has  given  this 
question  considerable  attention,  enumerates  a  rather  large  number  of 
monstrosities  more  or  less  directly  attributable  to  pruning.  Among  the 
more  important  of  these  maybe  mentioned  the  forcing  out  of  the  so-called 
"second-bloom"    from    the   limbs   and    trunks   of    pear  trees,  marked 


416  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

increases  in  size  and  changes  in  the  form  of  leaves,  fasciation  and  the 
metamorphosis  of  the  glands  of  apricot  leaves  into  small  leaflets.  He 
considers  these  abnormalities  to  be  due  to  an  upsetting  of  the  balance 
normally  existing  between  transpiration  and  assimilation.  It  should  be 
remembered,  however,  that  in  many  instances  these  abnormal  structures 
arise  independent  of  any  pruning. 

Amount  of  Pruning  Varying  with  Fruiting  Habit. — The  facts  just 
presented  on  the  results  to  be  expected  from  light,  moderate,  heavy 
or  no  pruning,  show  clearly  that  no  rigid  rules  can  be  stated  as  to  the 
amount  of  pruning  best  suited  to  orchard  trees  even  of  a  single  age  or  of  a 
single  kind.  However,  if  certain  other  pertinent  facts  and  principles 
be  considered,  the  amount  to  be  given  orchard  trees  becomes  somewhat 
more  easilj^  determined. 

The  fruit  grower  wishes  to  produce  as  soon  as  possible  a  tree,  shrub, 
or  vine  sufficiently  large  to  bear  crops  of  at  least  moderate  size.  It  is 
necessary,  furthermore,  that  the  plant  have  a  strong  framework  for  the 
support  of  the  smaller  branches  and  their  fruiting  wood  and  that  it  be 
adequately  equipped  with  the  spurs  or  shoots  that  bear  fruit  buds.  For 
the  first  year  or  several  years,  in  many  species,  fruit  production  is  neither 
expected  nor  desired.  The  maturing  of  fruit  and  to  a  certain  extent  even 
the  formation  of  fruit  buds  and  potential  fruiting  wood  might  tax  the 
energies  of  the  plant  so  that  increase  in  size  would  be  checked  seriously. 
A  little  later,  however,  when  the  tree  approaches  such  age  and  size  that  it 
can  begin  production  without  injury  to  its  general  welfare  the  grower 
desires  it  to  develop  gradually  (or  sometimes  quickly)  fruit-producing 
growth  and  he  wishes  to  keep  this  growth  actively  at  work.  As  the 
tree  becomes  still  older  its  natural  growing  habits  are  very  Hkely  to 
encumber  it  with  too  much  fruiting  wood,  more  than  its  roots  and  leaves 
can  supply  with  food  materials  for  heavy  and  regular  production.  The 
grower's  aim  then  should  be  to  get  rid  of  the  old  unproductive  wood 
or  to  invigorate  it  or  to  limit  the  formation  of  new  wood.  His  problem 
is  first  that  of  building  the  plant;  then  it  is  equipping  it  and  providing 
for  such  extensions  and  new  equipment  as  space  and  conditions  permit 
and  finally  it  becomes  a  problem  of  maintenance  at  maximum  efficiency. 

When  these  general  principles  are  considered  in  their  relation  to  the 
varying  results  attending  pruning  in  different  amounts,  it  is  evident  that, 
in  general,  tree,  bush  and  vine  fruits  should  be  pruned  heavily  when  young 
to  secure  a  strong,  stocky  framework  with  well  spaced  limbs  and — of 
equal  importance — to  prevent  the  production  of  fruit  and  even  of  fruiting 
wood  As  the  plant  approaches  bearing  age  and  size,  pruning  should  be 
less  severe,  to  permit  or  encourage  the  production  of  fruiting  wood. 
Perhaps  in  extreme  cases  it  may  be  desirable  at  this  stage  to  do  no  pruning 
at  all.  As  the  plant  becomes  still  older,  pruning  is  again  increased  in 
severity,  thus  limiting  or  sometimes  reducing  the  amount  of  fruiting 


PRUNING— THE  AMOUNT  OR  SEVERITY 


417 


wood  and  in  this  way  concentrating  the  energies  of  the  tree  upon  a  better 
support  of  what  is  left.  The  lower  line  shown  in  Fig.  49  gives  graphically 
some  idea  of  the  manner  in  which  the  amount  of  pruning  should  vary  with 
age  in  the  average  apple,  pear,  plum  or  cherry  tree  which  is  rather  slow 
growing  at  first  and  bears  principally  on  spurs.  Of  course  as  the  trees 
vary  in  vigor,  rapidity  of  growth,  fruiting  habits  and  in  other  respects 
there  should  be  accompanying  changes  in  the  severity  of  the  annual 
pruning.  Thus  the  peach  ordinarily  begins  bearing  at  an  earlier  age 
than  the  apple  or  cherry.  Consequently  it  should  be  pruned  to  leave 
fruiting  wood  and  permit  bearing  earlier.  Furthermore,  since  it  bears 
fruit  only  on  shoots  of  the  preceding  year,  regular  production  depends 
on  annual  provision  for  a  good  supply  of  new  shoots.  If  these  are  to  be 
produced  on  the  lower  part  of  the  tree  where  the  weight  of  the  fruit  will 
not  place  an  excessively  severe  strain  upon  the  crotches  comparatively 
heavy  annual  pruning  is  necessary.     At  no  stage  in  the  life  of  the  peach 


Age 

Fig.  49. — Graphs  showing  relative  amounts  of  pruning  required  for  the  peach  and  apple  at 

different  ages. 


tree  is  it  necessary  practically  to  discontinue  pruning  in  order  to  develop 
fruiting  wood  and  bring  it  into  bearing.  The  upper  line  in  Fig.  49 
shows  roughly  how  the  amount  of  pruning  desirable  for  trees  of  this  kind 
varies  with  age.  Similarly  it  is  possible  to  draw  graphs  for  the  amounts 
of  pruning  required  by  trees  of  other  kinds.  It  should  be  emphasized, 
however,  that  these  will  vary  in  details  not  only  with  different  kinds  of 
fruits,  but  with  varieties  of  the  same  kind  and  for  the  same  variety 
from  place  to  place  and  under  varying  soil  and  environmental  conditions. 
Summary. — By  and  large,  unpruned  trees  increase  in  size  more  rapidly 
than  pruned  trees  of  the  same  kinds  and  the  dwarfing  effect  of  pruning 
is  more  or  less  directly  proportional  to  its  severity.  This  dwarfing 
effect  is  a  result  not  so  much  of  the  production  of  less  new  shoot  growth 
each  year  as  of  the  amounts  of  wood  removed.  The  dwarfing  effect 
of  top  pruning  extends  to  the  root  system  because  of  the  reduction  in 
total    leaf    area.     Pruning    generally    results  also  in  a  diminution  in 


418  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

the  number  of  fruit  spurs  in  spur  producing  species,  though  there  may 
or  may  not  be  a  corresponding  reduction  in  number  of  fruit  buds  and 
in  the  resulting  yield.  Within  certain  limits  it  tends  to  increase  the 
size  of  the  fruit.  Extremely  heavy  pruning  may  occasionally  result 
in  different  types  of  abnormal  growth,  such  as  fasciation.  The  severity 
of  pruning  that  is  desirable  depends  on  many  conditions,  the  age  of 
the  tree  and  its  bearing  habit  being  among  the  more  important. 


CHAPTER  XXIII 
PRUNING— THE  METHOD 

It  seems  strange  that  a  horticultural  practice  as  old  as  pruning  should 
have  come  down  to  the  present  with  so  little  realization  that  it  includes 
questions  of  kind  as  well  as  of  amount  and  of  season.  Nevertheless,  most 
of  the  literature  is  silent  on  this  matter,  as  though  all  pruning  were 
necessarily  the  same  in  kind,  except  perhaps  for  the  innumerable  detailed 
ways  of  cutting  to  certain  buds  or  of  leaving  certain  spurs  or  shoots  for 
replacement  purposes.  The  fundamental  differences  between  essen- 
tially distinct  practices  have  not  been  generally  recognized.  Instead, 
attention  has  been  focused  upon  the  minute  and  less  important  details 
of  procedure.  Without  doubt  this  lack  of  realization  that  pruning  may 
vary  greatly  in  kind  and  that  entirely  different  results  attend  distinct 
kinds  or  types  of  pruning  has  been  responsible  for  much  of  the  confusion 
and  apparent  contradiction  that  is  evident  on  comparison  of  the  reports 
of  various    writers  and  investigators. 

Heading  Back  and  Thinning  Out. — A  number  of  classifications  of 
pruning  as  to  kind  are  possible.  However,  none  is  more  serviceable  than 
one  which  recognizes  the  difference  between  heading  back  and  thin- 
ning out.  It  is  difficult,  if  not  impossible,  to  differentiate  absolutely 
between  the  two  for  sometimes  the  removal  of  a  branch  or  part  of  a 
branch  is  at  the  same  time  a  thinning  out  and  a  heading  back.  In 
general,  however,  the  differences  between  the  two  are  clear  and  evident 
even  to  a  casual  observer.  Thinning  out  removes  entirely  a  shoot,  spur, 
cane,  branch,  limb,  or  whatever  the  part  may  be;  heading  back  removes 
only  a  portion,  leaving  another  portion  from  which  new  growths  can 
develop. 

Influence  on  New  Shoot  and  New  Spur  Formation. — Theoretically  a 
heading  back  that  is  equal  in  severity  to  a  certain  thinning  out  removes 
approximately  the  same  amount  of  wood  and  the  same  number  of  buds. 
In  practice  however,  there  is  a  considerable  difference.  A  thinning  out 
that  removes  50  per  cent  of  the  shoots,  gets  rid  of  just  half  the  amount 
of  wood  of  the  past  season  and  just  half  of  the  total  number  of  buds, 
both  lateral  and  terminal.  On  the  other  hand  a  50  per  cent  heading 
back  removes  somewhat  less  than  half  the  weight  of  woody  tissue  formed 
the  past  season  and  somewhat  more  than  half  the  total  number  of  new 
buds,  for  it  removes  an  equal  number  of  the  lateral  buds  and  all  the 
terminals.     A  heading  back  that  is  equal  in  severity  to  a  certain  thinning 

419 


420 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


out  is  therefore  more  severe  in  one  respect  and  less  severe  in  another. 
If  the  pruning  is  comparatively  heavy  the  difference  is  slight,  but  if  the 
pruning  is  light  the  difference  is  correspondingly  greater. 

Observation  shows  that  when  growth  begins  the  terminal  and  sub- 
terminal  buds  are  usually  the  first  to  start  and  in  the  majority  of  decidu- 
ous trees  and  vines  (less  frequently  in  shrubs)  they  produce  the  longest 
and  strongest  shoots,  though  shoots  may  grow  from  many  of  the  lower 
buds.     However,  seldom  do  all  the  lateral  buds  start  and  as  a  rule  the 


Fig.  50. — Grimes  apple  tree,  showing  a  typical  response  to  heading  back.     Compare  with 


Fig.  51 


largest  percentage  of  those  that  remain  dormant  are  on  the  basal  portion 
of  the  shoot.  Those  species  that  bear  principally  on  spurs  form  these 
spurs  mainly  from  buds  on  the  median  and  terminal  portions  of  the 
shoot.  Heading  back,  therefore,  limits  fruit  spur  formation  to  a  greater 
extent  than  a  correspondingly  heavy  thinning  out.  This  is  obvious 
from  the  data  presented  in  Table  11,  showing  the  amounts  of  shoot 
growth  and  the  numbers  of  spurs  formed  by  vigorous  5-year-old  apple 
trees  of  different  varieties  that  had  been  headed  back  or  thinned  out 


PRUNING— THE  METHOD 


421 


with  equal  severity.  However,  the  influence  on  fruit-spur  formation 
of  heading  as  compared  with  thinning  out  is  much  more  pronounced  in 
some  varieties  than  in  others.  Gano,  for  instance,  showed  practically 
no  difference  in  this  respect. 

Even  more  striking  than  the  inequality  in  numbers  of  spurs  from  the 
two  kinds  of  pruning  was  that  in  the  amount  of  new  shoot  growth. 
Heading  back  invariably  led  to  greater  shoot  production  than  a  corre- 
sponding amount  of  thinning  out  (see  Table  11).     In  Esopus  the  amount 


Fig.  51. — Grimes  apple  tree,  showing  a  typical  response  to  thinning  out.     Compare  with 

Fig.  50. 


of  new  shoot  growth  was  almost  double  that  in  the  thinned  trees.  Appar- 
ently thinning  out  some  of  the  shoots  in  a  tree  does  not  result  in  diverting 
the  same  amount  of  food  and  moisture  they  would  have  used  into  the 
remaining  unpruned  shoots.  Certainly  it  does  not  result  in  a  suffi- 
ciently increased  new  shoot  growth  from  them  to  compensate  for  that 
which  would  ordinarily  have  grown  from  the  portion  of  the  top  that 
has  been  pruned  away.  It  has  some  stimulating  influence  of 
this  kind  but  it  also  results  in  a  reduction  in  the  total  new  growth  formed. 


422 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


On  the  other  hand  heading  back  has  a  more  stimulating  influence  and 
the  pruned  shoots  tend  to  give  rise  to  as  much  (often  more)  new  shoot 
growth  as  would  have  arisen  from  the  unpruned  tree.  This  is  well 
illustrated  by  Figs.  50  and  51  which  show  the  response  of  two  trees  of 
Grimes  to  the  same  amount  of  pruning,  the  tree  on  the  left  having  been 
headed  back  and  that  on  the  right  having  been  thinned  out. 


Table    11. — Influence   of   Heading   Back   and   Thinning  Out  on  Shoot  and 
Spur  Formation  in  Young  Apple  Trees 

{After  Gardner^'') 


o  a 


«  M  6 


e-^2 


Grimes 
Grimes 
Grimes 
Grimes 
Gano . . 
Gano .  . 
Gano. . 
Gano. . 
Rome. 
Rome. 
Rome. 
Rome. 
Esopus 
Esopus 


26-50 
2&-50 
51-75 
51-75 
26-50 
26-50 
51-75 
51-75 
26-50 
26-50 
51-75 
51-75 
46-76 
4fr-76 


697 
731 


450 
462 
560 
562 
507 
508 
1007 
682 
444 
461 


2297 

82 

2495 

83 

1315 

22 

1362 

23 

2376 

15 

2609 

14 

2493 

15 

2435 

15 

1990 

9 

1956 

10 

2851 

9 

2230 

8 

1659 

28 

1813 

28 

Thinning 
Heading 
Thinning 
Heading 
Thinning 
Heading 
Thinning 
Heading 
Thinning 
Heading 
Thinning 
Heading 
Thinning 
Heading 


4123 
5703 
2308 
3328 
4577 
6293 
5072 
5846 
3352 
3915 
4785 
4474 
2122 
4031 


360 

322 

130 

101 

158 

158 

110 

111 

43 

25 

54 

25 

180 

144 


Influence  on  General  Shape  and  Habit. — Incident  to  quite  different 
effects  of  heading  and  of  thinning  upon  the  amount  of  new  shoot  growth 
and  the  number  of  new  spurs  are  the  influences  of  these  practices  on  gen- 
eral shape  and  growth  habit.  Thinning  out  places  no  check  on  the 
natural  tendency  to  grow  principally  from  the  terminal  and  subterminal 
buds.  Consequently  plants  pruned  exclusively  in  this  way  grow  tall 
and  wide  spreading  and  they  gradually  develop  a  more  open,  "rangy" 
habit  than  they  would  otherwise.  This  may  be  advantageous  or  dis- 
advantageous to  the  grower,  depending  on  a  number  of  conditions.  On 
the  other  hand  constant  heading  checks  this  tendency  to  extend  out  and 
up  and  results  in  a  plant  compact  in  habit  and  often  very  dense  in  growth. 
The  average  well  kept  hedge  furnishes  an  extreme  example  of  the  direc- 
tion in  which  all  heading  tends.  Indeed  much  of  the  usual  pruning  of 
the  bramble  fruits,  which  consists  largely  in  heading  back  both  leaders 
and  laterals  and  the  pruning  that  frequently  is  afforded  other  deciduous 
fruits — especially  when  they  are  young — results  in  a  type  of  growth  and 


PRUNING— THE  METHOD  423 

a  condition  of  tree  in  many  ways  closely  comparable  to  that  of  the  privet 
or  osage  orange  hedge. 

Influence  on  Fruit-hud  Formation  and  Fruitfulness . — The  orchard 
is  grown  and  maintained  not  primarily  for  its  shoot  growth  or  for  its 
spurs,  but  for  fruit.  The  grower  therefore  wishes  to  know  the  influence 
of  different  pruning  practices  on  fruit-bud  formation.  It  has  been 
shown  previously  that  this  occurs  at  varying  times  in  diverse  plants 
and  that  different  species  present  entirely  unlike  fruit  bearing  habits. 
That  is  to  say,  some  bear  on  spurs,  some  on  shoots;  some  bear  terminally, 
some  laterally.  If,  then,  pruning  practices  differ  greatly  in  their  influ- 
ences on  spur  formation  and  shoot  formation,  corresponding,  perhaps 
greater,  differences  may  be  expected  in  their  influences  on  fruit-bud 
formation  and  fruiting.  The  practice  that  leads  to  greater  fruitfulness 
in  one  species  may  tend  in  the  opposite  direction  in  another.  Thus 
heading  back  may  be  a  good  practice  in  growing  the  peach  because  it 
encourages  new  shoot  formation  on  which  the  fruit  buds  are  borne  and 
on  the  other  hand,  heading  back  may  be  a  bad  practice  for  the  pear, 
because  it  generally  limits  the  formation  of  fruit  spurs  on  which  most  of 
the  fruit  of  this  species  is  borne. 

In  contrast  to  thinning  out,  heading  back  generally  tends  not  only  to 
reduce  the  number  of  spurs  in  spur  bearing  species  but  also  to  lower  the 
percentage  that  differentiate  fruit  buds.  In  these  same  species,  thinning 
out,  though  it  may  reduce  somewhat  the  total  number* of  fruit  spurs,  has 
been  shown  under  some  conditions  to  lead  to  the  formation  of  fruit  buds 
and  to  the  maturing  of  fruit  on  a  larger  percentage  of  those  remaining. 
Data  on  this  question  obtained  from  pruning  experiments  with  j^oung 
apple  trees  in  Oregon  are  furnished  in  Table  12.  The  figures  presented 
in  the  last  three  columns  of  this  table  also  show  something  of  the  influence 
of  these  two  pruning  practices  on  fruit-bud  formation  on  shoots.  Though 
the  apple  is  not  generally  considered  a  shoot  bearer,  where  this  investiga- 
tion was  carried  out,  two  of  the  varieties  studied,  Rome  and  Gano,  bear 
principally  on  shoots  for  the  first  few  seasons.  Thinning  out  generally 
encouraged  terminal  and  lateral  fruit-bud  formation  on  shoots  more 
than  a  corresponding  heading  back,  though  there  were  some  exceptions. 
In  commenting  on  these  data  Gardner^-  says: 

"The  moderately  thinned  Grimes  trees  were  somewhat  more  than  twice  as 
productive  of  fruit  buds  as  the  correspondingly  headed  trees;  the  heavily  thinned 
Grimes  trees  were  10  times  as  productive  of  fruit  buds  as  correspondingly  headed 
trees.  The  moderately  thinned  Rome  trees  were  nearly  twice  and  the  heavily 
thinned,  nearly  five  times  as  productive  of  fruit  buds  as  those  correspondingly 
headed.  On  the  other  hand,  moderately  thinned  Gano  trees  produced  but 
slightly  more  fruit  buds  than  those  moderately  headed,  and  heavily  thinned 
trees  of  this  variety  averaged  distinctly  fewer  buds  than  those  heavily  headed. 
The  last  statement  also  holds  true  of  the  heavily  pruned  Esopus  trees.     A  more 


424 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Table  12. — Influence  of  Thinning  Out  and  Heading  Back  Shoots  on  Fruit- 
bud  Formation  in  the  Apple 
(After  Gardner'^-) 


•SS2 


i  ^ 


■3  c_ 

I&2 

III 

Us 

2;    '^ 

29.5 

2.7 

5.0 

24.8 

3.9 

4.6 

31.7 

2.6 

10,0 

8.9 

7.4 

2.2 

18.0 

0.9 

6.2 

0.1 

1.3 

1,0 

12.9 

59.3 

31.6 

14.8 

65.0 

16.4 

8.5 

43.5 

15.0 

14.6 

53.6 

13.7 

31.6 

3.5 

72.4 

5.6 

1.3 

47.5 

5.2 

5.3 

21.9 

5.0 

2.6 

51.7 

3.5 

2.8 

6.4 

41.9 

0.3 

10.4 

17.2 

0.1 

7.2 

11,4 

2.1 

17.6 

Grimes 
Grimes 
Grimes 
Grimes 
Grimes 
Grimes 
Gano. . 
Gano .  . 
Gano .  . 
Gano .  . 
Rome. , 
Rome. , 
Rome . , 
Rome . . 
Rome.  . 
Esopus 
Esopus 
Esopus 


No  pruning 
Thinning 
Thinning 
Heading 
Thinning 
Heading 
Thinning 
Heading 
Thinning 
Heading 
No  pruning 
Thinning 
Heading 
Thinning 
Heading 
No  pruning 
•Thinning 
Heading 


1-25 
26-50 
26-50 
51-75 
51-75 
26-50 
26-50 
51-75 
51-75 


26-50 
26-50 
51-75 
51-76 


41-76 
41-76 


402 

457 

360 

322 

130 

101 

158 

158 

110 

111 

142 

43 

25 

54 

25 

635 

180 

144 


37.2 
33.3 
44.3 
18.5 
25.1 
2.4 

103.8 
96. 
67. 
81, 

107. 
54. 
32. 
59. 


12,7 
52.6 
24.5 
31.1 


detailed  study  of  the  table  brings  out  a  number  of  additional  points.  In  the 
first  place,  it  is  noted  that  thinning,  as  compared  with  an  equally  severe  heading, 
almost  invariably  led  to  an  increased  production  of  fruit  buds  upon  fruit  spurs. 
The  one  exception  to  this  statement  is  furnished  by  the  heavily  headed  Gano 
tree,  a  variety  in  which  severe  heading  of  short  shoots  in  the  interior  seems  often 
to  have  the  effect  of  forcing  the  development  of  strong  fruit  spurs  from  the  remain- 
ing lateral  buds.  The  short  interior  shoots  of  other  varieties  do  not  show  such  a 
tendency  to  respond  to  severe  heading  in  this  way.  Heading-back  was  invariably 
accompanied  by  a  greater  development  of  terminal  fruit  buds  on  shoots  than 
thinning  out.  In  the  case  of  a  variety  like  Gano,  that  when  young  bears  a 
large  percentage  of  its  fruit  buds  in  this  way,  this  effect  may  be  sufficient  to  give 
the  tree  a  larger  total  number  of  fruit  buds  than  correspondingly  thinned  trees. 
Attention  is  called,  however,  to  the  fact  that  a  continuation  of  the  winter  heading 
year  after  year  would  remove  the  fruit  buds  on  all  the  shoots  headed  and  thus 
actually  result  in  decreased  flower  and  fruit  production  as  compared  with  thinning. 

"Another  point  worth  noting,  but  not  brought  out  in  the  table  is  the  fact 
that  the  shoots  bearing  terminally  average  much  shorter  in  the  thinned  than  in 
the  headed  trees.  They  are  generally  so  placed,  moreover,  that  in  the  thinning 
of  shoots  they  can  be  left  to  advantage  while  sterile  ones  are  taken  out. 

"Except  for  Esopus,  winter  thinning  of  shoots,  as  compared  with  heading, 
led  to  greatly  increased  production  of  lateral  fruit  buds  on  shoots.     In  the  case 


PRUNING— THE  METHOD  425 

of  the  heavily  pruned  Rome  trees,  the  proportion  of  such  lateral  fruit  buds  was 
8  to  1  under  the  two  pruning  treatments.  Furthermore,  the  distribution  of  these 
lateral  fruit  buds  is  such  that  a  given  heading-back  (for  instance,  50  per  cent) 
would  remove  a  much  larger  percentage  than  an  equall}^  severe  thinning  out. 
This  percentage,  in  the  case  of  Esopus,  would  be  enough  greater  more  than  to 
counterbalance  the  effect  upon  total  fruit  production  of  larger  numbers  of  such 
lateral  fruit  buds. 

"Taking  all  these  facts  into  consideration,  it  is  evident  that  the  effect  of 
thinning-out  and  likewise  of  heading  back  upon  fruit-bud  formation  varies 
greatly  with  the  variety.  The  pruning  practice  that  will  lead  to  the  largest 
fruit-bud  production  in  one  variety  will  not  necessarily  lead  to  it  in  another. 
Thus  it  becomes  important  for  the  grower  to  become- better  acquainted  with 
the  exact  fruiting  habits  of  his  varieties  under  his  conditions  as  well  as  to  the 
response  that  these  varieties  make  to  various  pruning  practices." 

Thinning  and  Heading  Lead  to  Different  Nutritive  Conditions. — The 
explanation  of  the  varying  effects  of  thinning  out  and  of  heading  back 
on  fruit-bud  formation  is  not  found  exclusviely  in  the  different  fruiting 
habits  of  the  several  species  and  varieties.  New  growth  is  made  chiefly 
at  the  expense  of  stored  foods,  particularly  carbohydrates.  In  the  section 
on  Nutrition  data  are  presented  showing  that  the  younger  wood  is 
comparatively  richer  in  food  reserves  than  older  tissues.  Heading  back, 
therefore,  removes  a  larger  amount  of  the  tree  reserves  than  a  correspond- 
ingly severe  thinning  out  and  leaves  it  less  able  to  recuperate,  especially 
if  the  pruning  has  been  severe. 

It  is  also  pointed  out  in  the  section  on  Nutrition  that  the  initiation 
of  the  fruitful  condition,  or  in  other  words  fruit-bud  formation,  is  associ- 
ated with  an  accumulation  of  carbohydrates  in  the  regions  where  fruit 
buds  can  be  formed.  Carbohydrate  accumulation  in  turn  depends  on 
carbohydrate  manufacture  on  the  one  hand  and  on  carbohydrate  utiliza- 
tion on  the  other.  When  the  latter  process  lags  behind  the  former,  oppor- 
tunity is  finally  afforded  for  the  laying-down  of  fruit  buds.  In  the  last 
analysis,  therefore,  pruning  influences  fruit -bud  formation  to  the  extent 
that  it  influences  carbohydrate  accumulation  or  carbohydrate  utilization 
or  the  status  of  the  ever  changing  ratio  between  them. 

Thinning  out  not  only  removes  less  stored  food  than  a  corresponding 
heading  back,  but,  as  just  pointed  out,  it  also  leads  to  increased  fruit- 
spur  formation  and  decreased  shoot  growth.  This  means  decreased 
carbohydrate  utilization  and  increased  carbohydrate  manufacture, 
because  spurs  are  short  growths  with  relatively  large  leaf  surfaces.  Their 
growth  is  made  very  early  in  the  season  and  from  then  on  they  are  manu- 
facturing and  accumulating  rather  than  spending  or  dissipating  organs. 
On  the  other  hand  heading  back  produces  fewer  of  these  short  growths 
and  more  of  the  longer  and  stronger  shoots  that  complete  their  growth 
much  later.     Consequently  they  more  nearly  exhaust  the  plant's  re- 


426  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

serves  than  the  shoots  and  spurs  of  thinned  trees  and  their  carbohydrate 
contributions  to  the  tree  as  a  whole  come  later  and  may  amount  to  less. 

Furthermore  the  thinned  is  more  open  than  the  headed  tree.  Its 
leaves  are  better  exposed  to  light  and  presumably  they  are  for  that  reason 
somewhat  more  effective  manufacturing  organs.  The  more  common 
formation  of  fruit  buds  in  the  better  exposed  parts  of  the  tree  is  evidence 
on  this  point.  The  rather  general  production  of  fewer  and  smaller  leaves 
on  spurs  in  the  interior  shaded  portions  of  compact  headed  trees,  in 
contrast  to  the  larger  and  more  numerous  leaves  on  the  spurs  of  open 
thinned  trees,  is  another  fact  pointing  to  material  differences  in  the  rate 
of  carbohydrate  accumulation  in  their  fruiting  wood. 

Still  another  reason  for  the  difference  in  response  from  heading  back 
and  from  thinning  out  lies  in  a  disturbance  of  an  equilibrium  within  the 
branch  itself  induced  by  heading  back.  Each  branch,  as  it  grows,  may 
be  regarded  as  a  system  in  equilibrium,  comparable  to  that  in  the  plant 
as  a  whole.  That  is,  there  is  a  balance  between  part  and  part.  If  a 
portion  of  the  branch  is  removed  this  balance  is  disturbed.  Equilibrium 
is  reestablished  by  regeneration  of  the  part  pruned  away.  Apparently 
little  readjustment  is  necessary  after  thinning  out,  because  the  equihb- 
rium  of  the  remaining  branches  is  not  disturbed.  The  adjoining  parts 
will  function  more  nearly  as  they  would,  had  no  pruning  been  done. 

The  Places  of  Thinning  and  of  Heading  in  Pruning  Practice. — The 
preceding  discussion  shows  that  no  rules  can.be  laid  down  as  to  the  relative 
amomits  of  heading  and  of  thinning  that  should  be  given  trees  of  a  certain 
kind  or  of  a  certain  age.  Rather  is  it  necessary  to  study  carefully  each 
problem  as  it  arises,  to  interpret  and  to  apply  the  general  principles  that 
have  been  pointed  out.  In  a  general  way,  however,  it  may  be  stated  that 
both  the  development  of  a  more  extensive  fruiting  system  and  more 
especially  the  better  and  more  efficient  functioning  of  that  system  are 
favored  more  by  thinning  than  by  heading.  There  are  notable  instances 
of  other  effects,  however,  e.g.  in  the  bramble  fruits,  in  which  the  heading 
back  of  the  canes  or  other  growth  limits  the  energies  of  the  plant  to  pro- 
duction on  the  remaining  shoots  or  spurs  and  causes  them  to  produce 
larger,  if  not  more,  fruits.  In  the  section  on  Fruit  Setting  it  is  pointed 
out  that  pinching  back  the  growing  shoots  of  the  grape  before  blossoming 
sometimes  leads  to  a  better  setting.  In  most  species  continued  thinning 
out  leads  eventually  to  tall  or  wide  spreading  and  "rangy"  plants,  plants 
that  require  wider  spacing  in  the  orchard,  that  often  make  undue  expense 
in  pruning,  spraying  and  other  care  and  that  are  unable  to  mature  their 
crops  without  a  great  number  of  mechanical  supports.  Judicious  heading 
back  corrects  these  tendencies  and  promotes  a  compact  type  of  growth 
that,  in  these  respects,  is  much  more  satisfactory.  In  fact  it  may  be 
stated  that  in  general  the  main  purpose  of  heading  back  is  to  control  the 
form  of  the  tree,  bush  or  vine — to  train  it.     In  practice  this  means  that 


PRUNING— THE  METHOD  427 

while  the  trees  are  young  they  should  receive  relatively  more  heading  back 
and  less  thinning  out,  because  they  are  then  being  trained.  As  they 
grow  older  they  should  receive  relatively  less  heading  and  more  thinning, 
because  they  will  require  less  and  less  training  for  shape  and  more  atten- 
tion to  the  proper  functioning  of  their  fruit-producing  wood.  Species  like 
the  peach  and  grape,  which,  because  of  their  growing  habits,  continually 
require  considerable  training  for  compactness  and  shape,  should  receive 
correspondingly  more  heading  when  mature  than  certain  other  species 
like  the  apple  or  walnut  that  have  entirely  different  growing  habits. 

Fine,  as  Compared  with  Bulk  Pruning. — In  pruning  practice  and  in  the 
consideration  of  pruning  problems  aside  from  those  dealing  with  the  heal- 
ing of  wounds,  pruning  is  generall}^  regarded  as  something  directly  affect- 
ing the  tree  as  a  whole.  It  is  common  to  speak  of  pruning  this  tree  heavily 
and  that  one  lightly,  of  heading  back  one  and  thinning  out  another,  of 
winter  pruning  in  one  instance  and  summer  pruning  in  another.  A  certain 
tree  having  been  neglected  for  a  number  of  years  is  said  to  require  a  heavy 
pruning  to  bring  it  back  to  a  vigorous  productive  condition.  Such 
sweeping  statements  disregard  frequent  cases  in  which  though  possibly 
certain  parts  of  the  tree  should  be  pruned  heavily,  certain  other  parts 
should  be  pruned  lightly,  if  at  all.  If  a  heavily  pruned  tree  fails  to  attain 
quickly  a  vigorous  productive  condition  there  is  query  why  the  result  has 
not  been  satisfactory.  When  it  is  decided  that  another  tree  requires 
only  a  light  pruning,  only  a  very  few  branches  are  removed.  If  such 
pruning  is  attended  by  some  of  the  results  usually  accompanying  heavy 
pruning  there  is  speculation  regarding  the  reason.  These  statements, 
which  will  be  recognized  as  based  upon  very  general  experience,  show  that 
pruning  is  regarded  somewhat  as  a  bulk  problem — as  something  which 
is  decided  on  for  the  tree  as  a  whole,  done  to  the  tree  as  a  whole  and  to 
which  the  tree  as  a  whole  responds.  Yet  the  results  frequently  obtained 
indicate  nothing  more  clearly  than  that  pruning  is  not  exactly  a  problem 
of  bulk. 

Results  Following  "Dehorning." — The  sucker  type  of  growth  that 
almost  invariably  follows  very  severe  cutting  back  or  "dehorning"  is 
well  known.  If  the  dehorning  has  been  done  in  winter  or  early  spring, 
numerous  comparatively  upright  shoots  are  produced  during  the  following 
summer.  The  usual  practice  is  to  thin  these  out  and  head  back  those 
that  are  left,  in  order  to  develop  as  quickly  as  possible  new  fruiting 
branches.  Thus  is  the  tree  "rejuvenated."  So  well  is  this  procedure 
understood  that  the  question  as  to  when  and  how  to  rejuvenate  trees  has 
been  considered  practically  settled.  However,  even  a  cursory  examination 
of  a  tree  that  has  recently  received  such  a  treatment  shows  that  only  a 
part  has  responded.  Undisturbed  branches  in  the  lower  part  of  the 
dehorned  tree  usually  continue  to  grow  in  the  ordinary  way.  Their 
spurs  bear  flowers  and  fruit  but  little  more  regularly  and  yield  a  product 


428 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


of  but  little  better  grade  than  before.  There  is  nearly  the  same  tendency 
for  their  older  spurs  and  smaller  fruiting  branches  to  become  gradually 
weaker  and  die.  Apparently  neither  as  whole  units  nor  in  their  separate 
parts  have  these  lower  branches  been  accelerated  or  retarded  in  growth. 
In  many  cases  they  do  not  even  produce  watersprouts,  such  as  develop  so 
abundantly  on  the  dehorned  branches  above  them.     In  other  words,  an 


Fig.  52. — A  Bartlett  pear  tree,  three  years  after  a  heading  back  of  the  main  upright 
limbs.  Notice  that  the  response  to  this  pruning  has  been  principally  close  to  where  the 
cuts  were  made. 


important — often  the  most  important — portion  of  the  tree,  apparently 
has  not  been  affected  in  any  way  by  the  dehorning.  This  is  brought  out 
clearly  in  Fig.  52.  The  treatment  has  resulted  merely  in  the  production 
of  new  wood  to  replace  a  portion  of  the  old  top. 

Even  more  striking  evidence  on  this  question  of  the  distance  to  which 
the  influence  of  pruning  extends  is  furnished  by  trees  that  have  been 
partly  dehorned,  that  is,  have  had  a  portion  of  their  branches  cut  back 


PRUNING— THE  METHOD 


429 


very  severely  and  others  of  equal  size  and  reaching  to  an  equal  height 
left  untouched.  In  such  instances  those  responses,  commonly  regarded 
as  characteristic  of  dehorning,  usually  are  limited  to  the  branches  that 
have  been  cut  back.  These  branches  produce  watersprouts  in  abun- 
dance, but  the  unpruned  branch  continues  to  grow  and  function  as  though 
nothing   had   been   done   to   upset   the   usual   conditions   in   the   tree. 


Fig.  53. — An  old  Italian  prune  tree.  All  of  the  main  limbs  but  one  were  cut  back  four 
years  before  this  picture  was  taken.  The  unheadcd  limb  in  the  center  shows  little  response 
to  the  pruning. 

Examples  of  this  occur  in  old  trees  of  many  species  that  are  being  top- 
worked,  when  the  process  is  being  distributed  over  a  period  of  several 
years.  The  influence  of  the  heavy  pruning,  incident  to  the  top  working 
process,  usually  is  not  reflected  to  any  appreciable  extent  in  a  changed 
manner  of  growth  in  the  ungrafted  limbs  (see  Fig.  53). 

Results  Attending  the  Removal  of  a  Few  Large  Limbs. — The  entire 
removal  of  one  or  more  comparatively  large  limbs,  the  majority  being 
left  unpruned,  is  a  type  of  pruning  in  more  or  less  sharp  contrast  to  the 
bulk  heading  back  just  discussed.  It  may  be  considered  a  kind  of  bulk 
thinning.     Many  fruit  growers  prune  in  this  manner,  which  possesses 


430  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

at  least  the  advantage  of  requiring  little  labor.  Experience  shows  that 
when  a  single  large  limb  is  removed  from  almost  any  part  of  a  tree,  water- 
sprouts  develop  to  take  its  place  and  the  rest  of  the  top  continues  to  grow 
as  before.  The  watersprouts  arise,  for  the  most  part,  not  from  limbs  far 
removed  from  the  pruning  wound,  but  close  to  the  point  where  the  cut 
was  made.  There  is  an  unmistakable  response  to  the  pruning,  but  that 
response  is  evident  within  a  very  limited  area.  The  tree  as  a  whole  does 
not  show  it. 

Those  who,  after  permitting  a  leader  to  develop  for  a  number  of  years 
and  to  form  a  close  centered  tree,  have  finally  tried  to  train  to  an  open 
center  or  vase  shape  can  furnish  abundant  evidence  on  the  question  under 
discussion.  The  removal  of  the  central  leader  from  trees  of  this  kind 
(bulk  heading  back  or  bulk  thinning  out,  depending  on  the  form  of  the 
tree  and  where  the  cut  is  made),  is  almost  always  followed  by  the  pro- 
duction of  a  number  of  watersprouts  that  tend  to  take  its  place.  The 
subsequent  removal  of  these  watersprouts  is  followed  by  the  production 
of  still  others,  nearly  always  at  points  near  the  wound  left  by  the  removal 
of  the  leader.  The  unpruned  branches  seem  little  influenced  by  the 
cutting  out  of  the  leader. 

In  attempting  to  train  young  Yellow  Newtown  apple  or  Bartlett  or 
Anjou  pear  trees  to  an  open  center,  or  the  Mcintosh  apple  or  Winter 
Nelis  pear  to  a  closed  center,  there  is  difficulty  in  keeping  these  trees 
from  growing  dense  in  the  center  in  the  first  instance  and  from  spreading 
out  or  even  growing  down  in  the  second,  though  the  shoots  are  cut  out  or 
off.  Furthermore — a  matter  of  equal  or  greater  importance — there  is 
difficulty  in  making  the  other  shoots  and  limbs  of  these  same  trees  spread 
out  or  grow  upright,  as  the  case  may  be  and  thus  profit  by  the  nutrient 
materials  that  it  is  desired  to  divert  from  the  closely  pruned  parts.  In 
fact  so  persistently  do  the  watersprouts  tend  to  replace  removed  limbs, 
that  the  easiest  way  to  develop  an  open  centered  tree  is  not  to  cut  out  all 
of  the  growth  in  the  center,  but  rather  to  suppress  it  by  pruning  it  a  little 
more  severely  than  the  surrounding  branches  that  are  desired  for  the 
main  framework.  Even  then  it  is  doubtful  if  the  usual  characteristic 
growth  of  the  remaining  branches  is  materially  changed.  Similarly,  when 
young  trees  are  lightly,  or  even  heavily,  headed  back  new  shoots  are  sent 
out,  but  mainly  from  points  where  some  of  them  can  easily  replace  the 
portion  removed.  It  is  not  common  for  distant  untouched  portions  of  the 
tree  to  show  a  well  defined  response  to  pruning. 

Results  Attending  Spur  Pruning. — As  they  become  older,  some 
varieties  of  apple  and  pear  trees  develop  large  numbers  of  fruit  spurs, 
which  often  branch  and  rebranch  until  they  become  fruit  spur  clusters. 
Usually  when  there  are  such  large  numbers  of  fruit  spurs  only  a  com- 
paratively small  percentage  can  flower  and  fruit  in  any  single  season  and 
the  record  of  any  single  spur,  or  even  spur  cluster,  especially  in  an  older 


PRUNING— THE  METHOD  431 

part  of  the  tree,  would  show  very  irregular  fruiting.  In  such  trees, 
though  there  is  little  vegetative  growth  in  the  general  acceptation  of  the 
term,  nearlj^  all  the  energies  of  the  tree  are  really  being  absorbed  in  a 
slow  vegetative  growth  of  the  spurs.  The  recognition  of  this  condition 
leads  the  grower  to  try  dehorning  or  some  other  type  of  bulk  pruning  as  a 
remedial  measure.  That  bulk  pruning  is  only  a  partial  remedy  has 
already  been  shown.  Occasionally  a  grower  tries  the  removal  of  a  part 
of  the  spurs  from  such  trees.  As  the  spurs  possess  a  very  large  percentage 
of  the  growing  points  and  bear  practically  all  of  the  leaf  system  of  a  tree 
in  such  condition,  a  thinning  of  spurs  is  in  one  sense  the  equivalent  of  a 
heavy  pruning  though  the  total  weight  of  the  wood  removed  may  be 
negligible.  When  treated  in  this  way  trees  produce  few  or  no  water- 
sprouts,  though  the  removal  of  a  few  large  branches  with  an  equivalent 
number  of  growing  points  leads  to  their  formation.  However,  the  re- 
maining spurs  grow  more  vigorously  and  the  new  shoots  developing  from 
lateral  and  terminal  buds  are  much  larger  and  stronger.  As  a  net  result 
though  the  tree  is  changed  httle,  if  at  all,  in  general  form,  the  rate  of 
growth  of  nearly  all  its  individual  parts  is  accelerated  and  the  ways  in 
which  they  function  are  materially  changed.  The  tree  as  a  whole  has 
been  affected  because  nearly  all  its  individual  parts  have  been  affected. 

Application  to  Practice. — A  consideration  of  the  points  that  have  been 
made  leads  unmistakably  to  at  least  one  conclusion:  namely,  that  the 
radius  of  influence  within  the  tree  of  any  pruning  (that  is,  the  cutting 
out  or  cutting  back  of  any  particular  shoot  or  branch)  is  comparatively 
small.  Parts  close  to  the  pruning  wound,  or  perhaps  close  to  a  space 
left  by  the  removal  of  a  branch,  respond  to  the  pruning  treatment.  Gen- 
erally speaking,  other  parts  of  the  tree  do  not.  In  other  words,  pruning 
does  not  appreciably  affect  the  tree  as  an  entity;  it  affects  the  whole  tree 
only  indirectly  through  its  effect  on  limited  portions.  To  stimulate  the 
formation  of  fruit  spurs  pruning  must  be  done  close  to  the  point  where 
they  are  desired  and  to  increase  the  productivity  of  spurs  already  present 
pruning  must  be  done  in  their  immediate  neighborhood.  This  in  turn 
means  light,  or  rather  fine,  as  opposed  to  coarse,  pruning.  It  is  neces- 
sary to  avoid  bulk  pruning  and  give  greater  attention  to  detail.  Theoret- 
ically pruning  should  concern  itself  mainly  with  shoots,  spurs  and  the 
smaller  branches  rather  than  with  older  and  larger  wood.  Practically 
some  exceptions  must  be  made,  particularly  in  trees  that  have  been 
neglected  for  several  years,  because  the  operation  must  be  conducted  with 
due  regard  to  economy.  The  finer  and  the  more  evenly  distributed  the 
pruning  the  more  expensive  it  is  and  the  net  returns  become  subject  to 
the  law  of  diminishing  returns.  Therefore  in  practice  the  most  profitable 
kind  of  pruning  is  always  a  compromise  between  the  type  which  is  best 
for  the  tree  and  the  type  which  can  be  done  most  cheaply. 

Most  of  the  trouble  from  fungous  or  bacterial  infection  comes  from 


432  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

the  large  wounds,  those  made  in  bulk  pruning.  This  is  not  an  important 
factor  in  the  culture  of  the  bush  or  vine  fruits  but  it  is  usually  of  consider- 
able importance  in  the  tree  fruit  plantation.  Indeed  it  is  not  too  much 
to  say  that  the  life  of  the  average  orchard  tree  is  reduced  by  one-third 
through  the  work  of  wound  fungi  and  bacteria.  Fine,  as  opposed  to 
coarse  or  bulk,  pruning  is  the  most  practicable  way  of  preventing  losses 
of  this  sort. 

Carrying  the  line  of  reasoning  a  step  further  it  becomes  evident  that 
pruning  should  be  regular  and  frequent.  This  is  a  statement  which  most 
growers  know  to  be  true  from  observation  and  experience,  though  the 
reasons  may  not  always  be  clearly  understood.  However,  the  points 
that  have  been  brought  out  furnish  an  explanation  of  some  of  the  charac- 
teristic results  following  irregular  pruning.  Trees  left  unpruned  for 
several  years  usually  seem  to  require  the  removal  of  some  of  the  larger 
branches  or  limbs.  This  approaches  the  bulk  type  of  pruning  and  stimu- 
lates new  vegetative  growth  more  than  it  invigorates  the  older  fruiting 
wood;  new  vegetative  growth  of  this  sort  is  as  likely  to  increase  as  to 
diminish  difficulties. 

What  has  been  stated  should  not  be  construed  as  condemnation  of 
occasional  heavy  pruning,  that  is,  the  removal  of  a  considerable  amount 
of  growth.  Though  heavy  pruning  as  commonly  done  is  bulk  pruning, 
it  is  not  necessarily  so.  It  may  consist  in  the  removal  of  a  large  amount 
of  shoot  growth  and  small  branches  and  instead  of  giving  rise  to  water- 
sprouts,  it  may  stimulate  the  normal  vegetative  growth  and  the  fruit 
spur  system.  The  spur  pruning  to  which  reference  has  been  made  is 
evidence  to  this  effect. 

Even  bulk  pruning  is  not  always  harmful.  There  are  occasions  when 
a  growth  of  strong  vigorous  shoots  or  watersprouts  is  desired  in  some  part 
of  the  tree.  Particularly  is  this  true  in  trees  that  have  suffered  from  win- 
ter injury  or  some  other  form  of  dieback.  Then  too,  it  should  be  remem- 
bered that  many  species  do  not  bear  on  fruit  spurs  or  on  short  growths  of 
any  other  kind.  Their  flower  buds  are  formed  freely  upon  their  longest 
and  strongest  shoots  and  bulk  pruning  which  leads  to  this  type  of  vege- 
tative growth  may  increase  rather  than  check  fruitfulness. 

Root  Pruning. — Root  pruning  has  long  been  a  recognized  practice 
among  many  European  fruit  growers,  particularly  those  of  the  British 
Isles  and  the  adjacent  continental  countries  and  for  many  years  it  was 
generally  recommended  (but  rarely  done)  in  the  United  States.  Though 
its  use  has  not  been  limited  to  trees  grown  as  dwarfs  it  has  been  employed 
much  less  commonly  with  standards.  In  this  country  particularly,  as  the 
culture  of  dwarf  fruit  trees  has  become  relatively  less  important,  root 
pruning  has  all  but  disappeared  from  the  list  of  cultural  operations. 
However,  a  certain  amount  of  root  pruning  is  almost  always  accomplished 
in  the  regular  cultivation  of  standard  orchard  trees.     For  this  reason, 


PRUNING— THE  METHOD  433 

though  tillage  is  thought  to  effect  a  root  pruning  seldom,  some  of  the 
more  important  effects  of  severing  a  portion  of  the  tree's  roots  at  different 
seasons  may  well  be  noted. 

In  the  culture  of  dwarf  trees  of  almost  any  kind,  Rivers,^^  one  of  the 
leading  exponents  of  the  practice,  recommended  an  annual,  or  at  least  a 
biennial,  shortening  of  all  the  roots.  In  describing  the  operation  he  said: 
"Open  a  circular  trench  18  inches  deep  around  the  tree,  18  inches  from 
the  stem,  and  cut  off  every  root  and  fibre  with  a  sharp  knife.  When 
the  roots  are  so  pruned,  introduce  a  spade  under  one  side  of  the  tree,  and 
heave  it  over  so  as  not  to  leave  a  single  tap-root;  fill  in  your  mould,  give  a 
top  dressing  of  manure,  and  it  is  finished.  The  diameter  of  your  circular 
trench  must  be  slowly  increased  as  years  roll  on;  for  you  must,  each  year, 
prune  to  within  1}^4  or  2  inches  of  the  stumps  of  the  former  year.  Your 
circular  mass  of  fibrous  roots  will  thus  slowly  increase,  your  tree  will 
make  short  and  well-ripened  shoots,  and  bear  abundantly."  It  is  gen- 
erally recommended  that  this  root  pruning  be  done  in  the  late  fall.  The 
major  repsonse  will  then  be  evident  the  following  spring  and  summer  in  a 
reduced  vegetative  growth  and  an  increased  formation  of  fruit  buds. 

Some  conception  of  the  dwarfing  influence  of  continued  root  pruning 
on  apples  grown  on  Paradise  stocks  is  afforded  by  an  investigation  con- 
ducted at  the  Woburn  Experiment  Station  in  England.  In  summa- 
rizing their  results,  Bedford  and  Pickering^  state:  "In  one  series  the 
trees  were  root-pruned  every  year,  in  another  every  other  year,  and  in 
a  third  every  fourth  year;  actual  lifting  from  the  ground  being  adopted, 
till  they  became  too  large  for  this  to  be  done  without  excessive  injury. 
The  check  caused  to  the  growth  of  the  trees  was  apparent  from  every 
point  of  view,  and  its  extent  may  be  gathered  from  the  weights  of  the 
trees  when  they  were  ultimately  removed.  Thus  with  the  Cox,  which 
were  removed  after  15  years,  the  weights  of  those  trees  which  had  been 
root-pruned  every  fourth  year  were  only  43  per  cent  of  those  which  had 
not  been  root-pruned;  where  the  operation  had  been  performed  every 
other  year,  the  weights  were  7  per  cent  of  the  non-treated  trees, 
and  with  the  yearly  operation,  3  per  cent;  indeed,  in  the  last  case,  the 
trees  had  scarcely  increased  in  weight  since  they  had  been  planted,  and 
had  been  dead  for  several  years  before  they  were  removed."  These 
investigators  then  state  that  root  pruning  is  followed  by  increased  crop 
production,  though  usually  this  is  not  evident  until  the  second  season 
after  the  operation.  However,  repeated  root  pruning  so  weakens  the 
trees  that  they  soon  fall  behind  non-treated  trees  in  yield.  Bedford 
and  Pickering  conclude  that  "root-pruning  is  an  operation  which  should 
be  practiced  with  extreme  moderation,  and  only  in  those  cases  where 
excessive  branch-growth  calls  for  stringent  measures."  The  root 
pruning  investigations  of  Drinkard^®  in  Virginia  led  to  practically  the 
same  conclusions.     He  reported  a  greatly  reduced  shoot  growth,  with 


434  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

leaf  areas  on  the  root  pruned  trees  only  5  to  20  per  cent  of  those  on  the 
checks.  Furthermore  the  leaves  of  the  treated  trees  were  smaller  and 
paler  than  those  of  the  untreated  trees.  This  check  in  vegetative 
growth  was  accompanied  by  an  increased  formation  of  fruit  buds;  these, 
however,  were  so  weak  that  comparatively  few  set  fruit  and  yields  were 
less  than  those  obtained  from  trees  not  root  pruned. 

The  experimental  results  of  these  and  of  other  recent  investigators 
do  not,  on  the  surface,  agree  with  the  opinions  of  many  of  the  earlier 
writers  regarding  the  desirability  of  root  pruning.  The  quotation 
from  Rivers,  however,  included  with  the  recommendations  for  annual 
or  biennial  root  pruning  one  for  liberal  applications  of  manure  and  a 
study  of  the  earlier  literature  dealing  with  this  subject  shows  that  arti- 
ficial feeding  and  often  artificial  watering  was  assumed  for  practically 
all  root  pruned  trees.  The  relatively  great  productivity  of  the  root 
pruned  dwarfs  of  European  and  other  gardens  therefore  should  be  re- 
garded as  due  only  partly  to  root  pruning,  some  of  the  other  attendant 
practices  being  perhaps  more  responsible. 

Seldom,  if  ever,  would  the  operations  incident  to  clean  culture  or 
any  other  system  of  soil  management  result  in  a  root  pruning  as  severe 
as  that  contemplated  in  the  regular  practice  that  goes  by  that  name. 
Nevertheless  the  deep  plowing  of  trees  growing  in  a  shallow  soil  or  in 
a  soil  that  compels  shallow  rooting  actually  effects  a  considerable,  and 
occasionally  a  very  severe,  root  pruning.  This  may  be  expected  to 
afford  a  temporary  stimulus  to  fruit-bud  production  and  at  the  same  time 
to  check  vegetative  growth  more  or  less,  though  either  or  both  of  these 
direct  effects  may  be  masked  by  the  indirect  influence  that  the  tillage 
exerts. 

Special  Pruning  Practices. — Stripping,  notching,  ringing  and  girdling 
may  be  considered  together  as  a  group  of  special  orchard  practices  rather 
closely  related  to  pruning.  The  names  used  to  designate  them  are  suffi- 
ciently descriptive  to  make  unnecessary  any  further  explanation  of  the 
procedure  involved.  They  are  all  performed  with  the  aim  of  so  control- 
ling the  translocation  of  elaborated  foods  that  their  accumulation  in 
certain  parts  may  lead  to  increased  fruit-bud  formation  and  hence  to 
greater  fruitfulness  or  to  a  better  setting  of  the  flowers  or  to  a  better 
development  of  the  fruit  itself. 

The  upward  movement  of  water  in  the  tree,  of  the  transpiration  stream, 
is  commonly  thought  to  occur  in  the  outer  layers  of  the  wood.  Knowl- 
edge of  the  translocation  of  elaborated  foods  is  rather  fragmentary, 
though  it  is  rather  generally  agreed  that  their  downward  movement 
is  through  the  phloem.  Recent  investigations  of  Curtis^*  indicate  that 
no  appreciable  quantities  of  carbohydrates  move  upward  through  the 
xylem  and  that  such  elaborated  food  materials  as  are  stored  in  the  xylem 
move  only  radially  in  the  wood.     Their  upward  transfer  is  limited  mainly 


PRUNING—THE  METHOD  435 

to  the  tissues  of  the  bark,  except  for  a  limited  translocation  by  means  of 
_  diffusion.  Consequently  those  portions  of  shoots  or  branches  above  the 
point  where  the  flow  of  elaborated  foods  has  been  checked  by  girdling 
or  ringing  depend  on  their  own  resources  in  so  far  as  elaborated  foods 
are  concerned.  That  is,  they  cannot  receive  foods  manufactured  else- 
where in  the  plant  and  foods  that  they  manufacture  must  be  stored 
within  their  tissues  or  utilized  by  them.  If  the  operation  is  performed 
during  the  dormant  season  or  very  early  during  the  growing  season, 
vegetative  growth  above  the  ringed  or  girdled  point  will  be  checked 
because  of  the  early  exhaustion  of  the  stored  carbohydrates  and  the 
reduced  leaf  area  will  limit  the  synthesis  of  a  new  supply.  On  the  other 
hand,  this  new  supply  that  is  synthesized  cannot  be  translocated  to 
the  roots  or  other  parts  of  the  tree  and  must  be  stored  or  utilized  in 
close  proximity  to  its  point  of  manufacture.  Girdling  or  ringing  after 
the  first  flush  would  permit  a  greater  amount  of  growth  beyond  the 
point  of  operation  because  food  stored  elsewhere  would  be  to  some  extent 
available  for  this  new  growth  and  following  the  ringing  there  would  be 
opportunity  for  a  correspondingly  greater  accumulation  of  foods.  The 
general  influence  of  notching  and  stripping  is  in  the  same  direction  as 
that  of  ringing,  but  is  less  pronounced  because  the  operations  themselves 
only  partl}^  stop  translocation  through  the  phloem. 

It  is  evident  that  the  effect  of  any  of  these  special  practices  on 
accumulation  and  concentration  of  food  materials  is  almost  certain  to 
be  more  pronounced  in  the  summer  than  it  is  during  the  spring  months. 
This  explains  why  they  so  often  fail  to  encourage  the  formation  of  fruit 
buds  and  greater  fruitfulness  for  which  they  have  been  so  frequently 
recommended,  the  period  of  fruit-bud  differentiation  having  passed  before 
their  concentrating  effects  are  realized. 

The  following  quotation  from  Drinkard's'*  summary  of  his  work  in  Virginia 
bears  on  this  point:  "Ringing  at  different  seasons  when  accompanied  by  or 
preceded  by  spring  pruning,  of  the  branches  produced  no  noticeable  stimulation 
of  fruit  bud  formation.  Ringing  at  the  time  growth  was  resumed  in  the  absence 
of  spring  pruning  did  not  stimulate  fruit  bud  formation.  The  treatment  was 
given  too  early.  Ringing  at  the  time  the  foliage  was  fully  developed  in  the 
absence  of  spring  pruning  gave  the  best  results ;  however,  when  the  treatment  was 
given  at  the  time  the  fruit  buds  began  to  become  differentiated  there  was  some 
stimulation  to  fruit  bud  development.  Stripping  at  different  seasons  when 
accompanied  by  or  preceded  by  spring  pruning,  had  no  stimulative  effect  on 
fruit  bud  formation.  The  effects  of  stripping  were  offset  by  those  of  spring 
pruning.  Stripping  at  the  three  seasons  ah-eady  mentioned,  in  the  absence  of 
spring  pruning,  stimulated  fruit  bud  formation  uniformly." 

The  facts  relating  to  food  translocation  and  manufacture  may  also 
partly  explain  why  ringing  so  frequently  results  in  an  increase  in  size  or 
in  some  modifications  of  the  texture  or  composition  of  the  fruit  that 


436  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

matures  during  late  summer  or  in  early  fall.  Thus  DanieP^  reports 
a  marked  increase  in  size  of  the  fruits  of  the  tomato  and  egg-plant  from 
ringing;  Paddock,^"  Bioletti*^  and  Husman-'*  have  reported  a  similar 
increase  in  grapes.  On  the  other  hand  Howe^^  found  no  increase  in 
size  of  fruit  in  ringed  apples,  pears,  cherries  and  plums,  though  he  reports 
other  late-season  effects  in  the  earlier  maturity  of  fruit  and  a  much 
earlier  dropping  of  the  foliage  Paddock^^  likewise  has  reported  an 
earlier  maturity  of  grapes  borne  on  ringed  shoots,  an  earliness  sometimes 
amounting  to  as  much  as  two  weeks.  It  has  been  noted  frequently 
that  grapes  borne  on  ringed  shoots  contain  relatively  less  sugar  and  more 
acid^^  or  are  somewhat  poorer  in  quality^ ^  than  those  borne  on  untreated 
shoots. 

In  the  section  on  Fruit  Setting  ringed  shoots  of  the  grape  and  of 
certain  other  fruits  are  mentioned  as  setting  in  many  cases  a  larger  per- 
centage of  their  blossoms  than  those  not  treated  in  this  way,  if  the  opera- 
tion is  performed  just  previous  to  the  opening  of  the  flowers.  Seldom  is 
the  difference  great  enough  to  make  the  operation  worth  while  for  this 
purpose.  A  few  varieties  of  the  grape,  however,  without  such  treatment 
grow  so  vigorously  that  they  set  but  little  fruit  and  with  them  the  opera- 
tion should  be  performed  annually.  Thus  in  the  Fresno  (California) 
Experiment  Vineyard  12-year-old  ringed  Panariti  grafts  on  10  different 
resistant  stocks  averaged  7.5  tons  per  acre  during  1917  and  1918,  while 
unringed  vines  on  the  same  stocks  and  under  the  same  conditions  aver- 
aged 2.3  tons  per  acre.^^ 

From  the  data  presented  here  and  in  the  section  on  Nutrition  it 
is  evident  that  the  concentrating  influence  of  ringing,  stripping  and 
related  practices  depends  not  alone  on  their  effects  on  new  vegetative 
growth,  leaf  area  and  food  manufacture,  but  also  on  food  utilization. 
In  turn  the  utilization  of  the  elaborated  foods  that  are  synthesized  in  the 
shoot  beyond  the  point  of  ringing  depends  on  the  available  water  and 
nutrient  supply.  If  the  soil  is  comparatively  dry  and  low  in  nitrates,  the 
effect  of  ringing  or  related  practices  may  be  quite  different  than  with  an 
abundant  supply  of  both  moisture  and  nutrients,  because  the  products 
of  synthesis  beyond  the  ringed  point  may  be  utihzed  in  an  entirely 
different  manner.  This  factor  has  received  very  little  consideration  and 
it  must  be  properly  evaluated  before  any  ringing  operation  can  be  per- 
formed with  certainty  of  its  effects  on  either  fruit  bud  formation  or  on  the 
development  of  fruit.  Inadequate  consideration  of  this  factor  has  caused 
much  apparent  contradiction  and  uncertainty  in  the  results  attending  this 
group  of  practices. 

In  at  least  one  respect  there  is  general  agreement  among  those  who  have 
employed  ringing,  stripping  or  other  operations  to  check  the  transfer  of 
food.  They  all  report  a  tendency  to  check  the  growth  of  the  plant  during 
later  years  and  thus  have  a  dwarfing  influence.     This  is  proportional  to 


PRUNING—THE  METHOD  437 

the  degree  of  starvation  of  the  roots  through  separation  from  their  supply 
of  elaborated  foods  and  its  ultimate  effect  on  growth  and  development  is 
in  every  way  comparable  to  the  results  attending  root  pruning.  It 
should  be  mentioned  also  that  ringing  inflicts  mechanical  injuries  that 
sometimes  heal  slowly  and  for  this  reason  alone  it  should  be  used  with 
great  caution,  if  at  all,  on  certain  fruits  like  the  plum  and  cherry.  Appar- 
ently with  the  grape  alone,  among  the  connnon  deciduous  fruits,  should 
this  group  of  practices  be  a  regular  cultural  treatment  and  even  in  the 
grape  only  a  very  few  of  the  most  vigorously  growing  varieties  can  be 
ringed  with  profit.  Other  cultural  treatments  may  be  combined  and 
employed  to  better  advantage  to  bring  about  the  same  conditions  that 
these  special  practices  induce  and  with  far  less  danger  of  undesirable 
after-effects. 

Summary. — In  kind  all  top  pruning  may  be  considered  either  as 
heading  back  or  as  thinning  out.  These  two  kinds  produce  quite  differ- 
ent results,  particularly  as  the  pruning  increases  in  severity.  In  general, 
thinning  out  is  accompanied  by  less  new  shoot  growth  but  more  new  spur 
and  fruit-bud  formation  than  correspondingly  severe  heading  back. 
Heading  back  tends  to  make  trees  more,  and  thinning  out  less,  compact 
in  habit.  The  different  responses  from  the  two  methods  of  pruning  are 
due  probably  in  large  part  to  the  distinct  nutritive  conditions  to  which 
the  practices  give  rise.  Both  methods  have  their  places  in  orchard  man- 
agement, heading  l)ack  being  more  viseful  in  keeping  the  tree  well  shaped 
and  thinning  out  in  developing  its  fruiting  wood  and  in  keeping  that  wood 
in  good  working  order.  As  most  trees  grow  older  they  should  receive 
relatively  more  thinning  out  and  less  heading  back. 

In  kind,  pruning  may  be  coarse  or  fine  with  essential  differences 
in  the  attendant  responses.  Coarse  or  bulk  pruning  tends  to  disturb 
seriously  the  equilibrium  within  the  plant  and  generally  results  in  the 
production  of  watersprouts.  Careful  fine  pruning,  on  the  other  hand, 
evokes  a  much  more  general  response.  The  ideal  pruning  is  fine,  as 
opposed  to  coarse  or  bulk;  however  in  practice  a  compromise  must  gen- 
erally be  made  between  the  kind  which  is  best  for  the  tree  and  the  kind 
which  is  most  economical. 

Root  pruning  has  a  dwarfing  influence  and  its  greatest  use  is  in  the 
culture  of  dwarf  trees.  The  supposed  influence  of  root  pruning  in  pro- 
moting fruitfulness  is  due  probably  in  part,  if  not  largely,  to  other  prac- 
tices such  as  irrigation  and  fertilization  which  generally  accompany  the 
culture  of  dwarfs. 

Girdling,  notching,  ringing  and  stripping  are  special  practices,  related 
to  pruning,  which  have  for  their  object  the  promotion  of  fruitfulness 
through  interrupting  the  translocation  of  foods.  Their  use  is  attended 
by  uncertain  results  and  they  are  not  to  be  recommended  under  average 
conditions. 


CHAPTER  XXIV 

PRUNING— THE  SEASON 

The  subject  of  pruning  has  been  shown  to  present  three  major  aspects, 
one  of  which  is  a  consideration  of  the  varying  response  from  pruning  at 
different  seasons.  Theoretically  at  least  this  involves  a  study  of  the 
different  effects  from  pruning  each  successive  month,  or  perhaps  at  more 
frequent  intervals.  Practically  the  question  is  much  less  complicated, 
involving  principally  a  comparison  of  the  effects  attending  pruning  during 
the  growing  season  with  those  following  winter  pruning. 

Pruning  at  Different  Times  During  the  Dormant  Season. — Prun- 
ing at  different  times  during  the  dormant  period  may,  however,  re- 
ceive brief  consideration.  Dormant  or  winter  pruning  is  generally 
understood  to  mean  late  winter  or  early  spring  pruning,  since  it  is  usually 
done  then.  Winter  pruning,  however,  may  begin  as  soon  as  the  plants 
become  more  or  less  dormant  in  the  fall  and  may  continue  into  the  spring 
until  vegetation  is  starting  actively.  The  supposed  advantages  and 
disadvantages  of  pruning  at  different  times  during  the  dormant  period 
have  been  long  discussed.  Apparently  so  far  as  any  effect  on  the  amount 
and  character  of  subsequent  growth  is  concerned  there  is  little  or  no 
difference.  This  is  brought  out  clearly  by  experimental  work  with  apples 
in  England*  and  in  Minnesota^  and  with  grapes  in  New  York.^*  On  the 
other  hand  since  there  is  a  gradual  translocation  of  food  materials  from  the 
canes  to  the  trunk  and  roots  of  the  grape  during  a  3-  or  4-weeks  period 
following  leaf  fall,"*^  pruning  before  this  translocation  is  complete  or  after 
the  reverse  movement  has  begun  in  the  spring  should  result  in  a  some- 
what greater  check  to  vigorous  growth  of  the  vine  than  a  corresponding 
pruning  during  the  period  between  these  extremes.  This  effect  has 
been  noted  both  in  France*"  and  in  California.^ 

In  California  the  time  of  winter  pruning  has  been  found  to  be  impor- 
tant in  determining  when  grape  vines  of.  the  Vinifera  group  start  growth. 
Vines  pruned  immediately  after  the  fall  of  the  leaves  started  earliest; 
those  pruned  in  midwinter  started  about  4  days  later  and  those  pruned 
considerably  later,  when  bleeding  commenced,  were  delayed  about  6  days. 
"Pruning  when  the  terminal  buds  commenced  to  swell  retarded  the 
lower  buds  11  days,  and,  when  the  terminal  buds  had  grown  2  or  3  inches, 
20  days."^  In  other  words  the  lateness  of  starting  of  the  buds  was  in 
the  order  of  the  lateness  of  the  pruning. 

In  commenting  on  some  of  the  practical  applications  of  these  facts  in  grape 
culture  in  California  Bioletti''  remarks:  "The  retardation  of  the  starting  of  the 

438 


PRUNING— THE  SEASON  439 

shoots  in  the  spring  may  be  a  valuable  means  of  escaping  the  injurious  effects  of 
spring  frosts.  In  one  of  our  tests,  the  crop  on  nine  rows  pruned  Mar.  13,  was 
saved,  while  that  of  12  rows  pruned  Nov.  19,  and  Dec.  21,  was  completely 
ruined  by  a  frost  on  Apr.  21.  Late  pruning  also  retards  the  blossoming  though 
somewhat  less  than  it  does  the  starting.  Pruning  as  late  as  March  may  retard 
the  blossoming  10  days.  The  time  of  ripening  is  also  influenced  slightly  in  the 
same  direction.  When  spring  frosts  occur,  this  influence  appears  to  be  reversed. 
The  vines  pruned  early  may  blossom  and  ripen  their  fruit  later.  This  is  because 
the  frost  having  destroyed  the  first  shoots,  the  only  flowers  and  fruit  which 
appear    are    on    buds    which    have    started    after    the    frost  .    .    . 

"Pruning  may  be  done,  therefore,  in  frostless  locations  and  with  varieties 
which  set  their  fruit  well,  at  any  time  when  the  vines  are  without  leaves.  Where 
spring  frosts  are  common  the  pruning  should  be  as  near  the  time  of  the  swelling 
of  the  buds  as  possible.  The  benefits  of  late  pruning  without  its  inconveniences 
can  be  obtained  by  the  system  of  'double'  or  (clean)  pruning  practiced  in  some 
regions.  This  may  be  applied  in  various  ways.  The  simplest  is  to  shear  off  all 
the  canes  to  a  length  of  15  to  18  inches  at  any  time  during  the  winter  that  is 
convenient.  This  permits  plowing  and  other  cultural  operations,  and  the  final 
pruning  is  done  in  April.  A  better  method  is  to  prune  the  vine  as  usual  but  to 
leave  the  spurs  with  four  or  five  e.xtra  buds.  These  spurs  we  then  shortened 
back  to  the  proper  length  as  late  as  practicable.  In  some  cases  the  method 
practiced  in  the  Medoc  may  be  used.  This  consists  in  leaving  a  foot  or  15  inches 
of  cane  beyond  the  last  bud  needed  and  removing  all  the  extra  buds  at  the  time 
of  pruning.  The  base  buds  are  said  to  be  retarded  by  the  length  of  cane  above 
them  the  presence  of  buds  on  the  cane  having  no  effect." 

Pruning  late  in  the  dormant  season  is  quite  likely  to  be  attended  by 
more  or  less  bleeding.  Seldom  is  the  amount  great  enough  to  be  harm- 
ful though  many  growers  prefer  to  avoid  any.  In  a  few  species, 
as  for  example,  the  English  walnut,  late  pruned  trees  may  bleed  very 
profusely  and  the  moist  exposed  surfaces  offer  an  excellent  opportunity 
for  infection.  For  this  reason,  if  for  no  other,  fall  pruning  may  occa- 
sionally be  preferable  to  spring  pruning. 

Summer  Pruning. — In  the  discussion  of  the  effects  attending  various 
amounts  of  winter  pruning  there  was  shown  to  be  a  slower  net  increase  in 
size  with  pruned  than  with  unpruned  trees  and  the  more  severe  pruning 
was  shown  to  have  the  more  pronounced  retarding  influence.  Similar 
results  generally  follow  summer  pruning  and  for  about  the  same  reasons. 
The  real  question  is  whether  or  not  summer  pruning  has  a  greater  retard- 
ing effect  than  a  correspondingly  severe  winter  pruning  of  the  same  kind. 

Influence  on  Vegetative  Growth. — The  new  shoots  and  leaves  in  the 
spring  are  built  chiefly  at  the  expense  of  food  materials  formed  the 
preceding  season  and  stored  through  the  winter.  After  the  leaves  are 
fully  expanded  they  become  manufacturing  organs  and  eventually  return 
to  the  plant  a  supply  of  elaborated  foods  equal  to  or  in  excess  of  that 
consumed   in   their  development.     At   first,   however,   their  growth   is 


440 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


in  effect  parasitic  and  it  is  not  until  they  have  been  active  for  some  time 
that  they  have  fully  replaced  the  materials  used  in  their  growth.  Sum- 
mer pruning  removes  them  after  they  have  levied  their  tax  on  the 
tree's  reserve  foods  and  often  before  they  have  contributed  much  to  its 
welfare.  It  must  have,  generally,  a  greater  retarding  influence  on  net 
increase  in  size  than  a  correspondingly  heavy  winter  pruning.  This 
devitalizing  effect  of  summer  pruning  has  been  noted  by  many  observers 
and  recently  has  been  the  subject  of  a  number  of  experimental  studies. 
Alderman  and  Auchter^  found  that  young  summer  pruned  apple  trees 
averaged  only  120  feet  of  new  shoot  growth  in  1915  while  winter  pruned 
trees  of  the  same  age  and  of  the  same  varieties  averaged  188  to  216, 
according  to  the  severity  of  the  pruning.  The  summer  pruned  trees 
increased  in  spread,  height  and  circumference  more  rapidly  than  trees 
pruned  very  severely  in  the  winter,  but  much  less  rapidly  than  those 
pruned  moderately  or  lightly  in  the  winter.  Apple  trees  just  coming  into 
bearing  produced,  after  winter  pruning,  shoots  that  were  20  to  50  per 
cent  longer  and  10  to  20  per  cent  thicker  than  those  on  summer  pruned 
trees.  In  one  orchard  under  investigation  they  found  that  the  total  leaf 
area  of  summer  pruned  trees  averaged  only  from  299  to  459  square  feet, 
that  of  trees  pruned  both  summer  and  winter  averaged  from  527  to  794 
square  feet  and  that  of  trees  pruned  only  during  the  winter  averaged 
from  660  to  1144  square  feet.  Not  only  were  there  fewer  leaves  on  the 
summer  pruned  trees,  but  these  leaves  averaged  smaller  in  size.  The 
leaves  of  the  summer  pruned  trees  were  paler  and  yellowish,  suggesting 
an  additional  reduction  in  their  photosynthetic  abilities.  Arkansas  and 
York  Imperial  trees  in  full  bearing,  on  the  other  hand,  showed  practically 
no  difference  in  the  responses  to  summer  and  to  winter  pruning.  In 
fact  the  summer  pruned  trees  of  middle  age  produced  more  terminal 
shoot  growth  than  those  pruned  lightly  during  the  dormant  season, 
though  somewhat  less  than  those  pruned  heavily.  Table  13  presents 
data  obtained  in  England  from  pruning  back  weak  declining  plum  trees  at 
various  seasons.  The  figures  show  the  relative  lengths  of  the  new 
shoot  growth.  In  this  case  the  July  pruning  was  little  short  of  disastrous 
to  the  trees.  Certain  experimental  results  obtained  in  Virginia  from 
various  summer  and  winter  prunings  combined  with  special  practices 

Table  13. — Relative  Length  of  New  Shoots  of  the  Plum,  Cut  Back  at 
Different  Dates 
{After  Bedford  and  Pickering'^) 


May  27 

July  14 

Nov.  2 

Mar.  16 

May  15 

July  14 

Not  cut 
back 

1905 

1905 

1905 

1906 

1906 

1906 

125 

75 

100 

•   100 

65 

18 

67 

PRUNING— THE  SEASON 


441 


such  as  ringing,  stripping  and  root  pruning,  show,  despite  some  apparent 
inconsistencies,  that  pruning  during  the  growing  season  checks  new  shoot 
formation  and  increment  in  trunk  circumference  more  than  does  winter 
pruning.  19  Batchelor  and  Goodspeed,^  reporting  an  experiment  with 
young  bearing  Jonathan  and  Gano  apple  trees  in  Utah,  state  that  summer 
pruning  caused  reduced  vitaHty,  though  their  figures  show  that  the 
average  length  of  the  new  shoots  under  both  pruning  treatments  was 
practically  the  same  during  the  3  years  for  which  the  data  are  given. 
Summer  pruning,  however,  does  not  always  retard  growth  more  than 
winter  pruning.     Experiments  in  New  Jersey  showed  that  peach  trees 

Table    14. — Influence    ok    Early    Summer    Pruning    on   Shoot  Development 
IN  Young  Apple  Trees 
(After  Gardner-^) 


Average 

Average 

Average 

total 

shoot 

growth  for 

season, 
centimeters 

Average 

shoot 

shoot 

net  gain  of 

growth  re- 

growth re- 

tree in 

Variety 

Pruning  treatment 

moved  by 

moved  by 

shoot 

winter 

pruning, 

centimeters 

summer 

pruning, 

centimeters 

length  for 

season, 
centimeters 

Wagener 

Winter  pruned  only 

538 

2690 

2152 

Wagener 

Winter     and    sum- 

mer  pruned 

.533 

1611 

4250 

2106 

Yellow  Newtown 

Unpruned 

2720 

2720 

Yellow  Newtown 

Winter  pruned  only 

826 

3460 

2634 

Yellow  Newtwon 

Winter    and    sum- 

mer  pruned 

488 

1904 

4930 

2548 

Jonathan  

Unpruned 

3576 

3576 

Jonathan  

Winter  pruned  only 

967 

5165 

4198 

Jonathan  

Winter    and     sum- 

mer pruned 

941 

3837 

7430 

2652 

Grimes 

Unpruned 

2270 

2770 

Grimes 

Winter  pruned  only 

988 

2965 

1977 

Grimes 

Winter    and     sum- 

mer pruned. .... 

rm 

1603 

4360 

2256 

pruned  during  the  dormant  season  averaged  3,821  inches  of  new  shoot 
growth  in  1916,  while  those  pruned  in  the  summer  averaged  4,227.^ 
Though  this  difference  is  perhaps  not  much  above  experimental  error, 
it  at  least  indicates  that  summer  pruning  does  not  always  have  a  dwarfing 
influence.  In  Table  14  are  presented  data  obtained  in  Oregon  showing 
the  influence  on  shoot  development  in  young  apples  of  rather  severe 
early  summer  pruning.  In  kind  and  in  severity  the  summer  pruning 
treatment  was  practically  identical  with  that  given  in  the  winter.  In 
every  instance  the  summer  pruned  trees  produced  more  total  shoot 


442  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

growth — 58  per  cent,  in  the  Wagener  trees,  44  per  cent,  in  Yellow  Newtown, 
44  per  cent,  in  Jonathan  and  47  per  cent,  in  Grimes — than  those  that 
were  pruned  during  the  dormant  season  only.  A  part  of  this  increased 
growth  came  before  the  time  of  summer  pruning  (about  July  1),  but  the 
larger  part  of  it  was  produced  during  the  summer  months  following  the 
pruning.  The  growth  produced  before  the  time  of  summer  pruning  is  to 
be  regarded  as  the  consequence  of  a  summer  pruning  treatment  of  the  same 
kind  the  preceding  season;  the  growth  after  the  pruning  was  a  direct 
response  to  that  pruning.  There  was  practically  no  difference  between 
the  summer  and  winter  pruned  trees  in  their  net  increase  in  size,  except 
in  Jonathan.  The  winter  pruned  trees  of  that  variety  showed  a  greater 
net  growth,  principally  on  account  of  the  great  amount  of  wood  removed  by 
the  summer  treatment.  Vincenf*^  in  Idaho  has  reported  the  11-year 
record  of  an  apple  orchard  of  Jonathan,  Rome,  Grimes  and  Wagener  a 
part  of  which  received  only  winter  pruning  from  the  start  while  the  other 
part  received  only  summer  pruning  (Aug.  6  to  Sept.  6).  In  kind  and 
amount  the  pruning  of  the  two  portions  was  as  nearly  as  possible.  Table 
15  summarizes  some  of  the  growth  records  of  these  trees.  For  the  most 
part  the  average  heights,  widths  and  trunk  circumferences  were  slightly 
greater  in  the  winter  pruned  than  in  the  summer  pruned  trees,  while  the 
reverse  was  true  in  regard  to  average  shoot  lengths.  In  no  case,  how- 
ever, were  the  differences  large  enough  to  be  significant.  Clearly, 
summer  pruning  exerted  no  dwarfing  influence  in  this  orchard. 

These  almost  diametrically  opposite  results  attending  summer  pruning 
in  carefully  controlled  experimental  work  can  be  harmonized.  The 
tree  is  to  be  regarded  as  a  system  in  mobile  equilibrium.  This  equili- 
brium involves  a  condition  of  balance  between  part  and  part  and  between 
constituent  and  constituent  within  the  plant  and  a  condition  of  adjust- 
ment to  the  environment  without.  Chief  among  these  factors  of  environ- 
ment are  temperature,  light,  moisture  and  food  supply.  Growth  of  any 
kind  is  a  response  to  the  condition  of  the  equilibrium  within  and  of 
the  adjustment  without.  Pruning,  at  any  time — and  more  especially 
summer  pruning — disturbs  both  the  adjustment  to  the  environment 
without  and  the  balance  within.  The  immediate  effect  on  the  tree  as  a 
whole  of  any  summer  pruning  is  to  reduce  the  carbohydrate  supply 
and  the  rate  of  carbohydrate  manufacture  and  at  the  same  time  to 
increase  the  supply  of  water  and  other  nutrients,  particularly  nitrates, 
that  is  available  to  the  rest  of  the  plant.  The  size  or  amount  of  this 
influence  depends  on:  (1)  the  severity,  (2)  the  kind  and  (3)  the  time  of 
the  pruning  and  on  (4)  the  moisture  and  (5)  the  nutrient  supply  available 
in  the  soil.  Its  general  effect  on  growth  therefore  may  be  expected  to 
correspond  closely  to  that  of  fertilization  and  irrigation  at  that  particular 
time.  If  the  pruning  is  not  severe  enough  to  reduce  carbohydrate  sup- 
ply and  carbohydrate  manufacture  to  the  point  where  they  limit  new 


PRUNING— THE  SEASON 


443 


Table  15. — Growth  Records  of  Summer  and  Winter-pruned  Apple  Trees  in 

Idaho 

(After  VincenV^) 


Variety 

Pruning 

Average 

shoot 

length 

eleventh 

year,  inches 

Average 

height 

eleventh 

vear,  feet 

Average 

width 
eleventh 
year,  feet 

Average 

diameter 

eleventh 

year,  inches 

Jonathan 

Jonathan 

Winter 

Summer 

Winter 

Summer 

Winter 

Summer 

Winter 

Summer 

16.1 
18.2 
15.4 
14.8 
12.7 
16.2 
11.9 
12.4 

17.24 
15.98 
15.88 
15.75 
16.00 
15.38 
14.65 
14.30 

19.51 
17.71 
14.35 
13.60 
15.30 
14.67 
12.25 
12.95 

7.43 
7  35 

Rome 

6.58 
6  56 

Grimes 

Grimes 

6.71 
6  32 

Wagener 

Wagener 

5.82 
5.61 

tissue  formation,  active  growth  ensues.  This  apparently  is  the  explana- 
tion of  the  results  obtained  with  young  peach  trees  in  New  Jersey^  and 
with  young  apple  trees  in  Oregon,  ^i  Soil  conditions  were  such  and  the 
pruning  was  such,  in  time,  kind  and  severity,  that  a  vigorous  new  vegeta- 
tive growth  was  promoted  following  the  pruning  and  terminal  bud  forma- 
tion was  completed  at  a  considerably  later  date.  This  condition  may 
frequently  result  in  an  actual  increase  of  food  reserves  at  the  time  of  leaf 
abscission,  especially  in  sections  with  a  late  growing  season,  because  of  the 
greatly  increased  leaf  surface.  On  the  other  hand  if  the  pruning  is  of 
such  character  that  carbohydrates  and  other  elaborated  foods  are  re- 
moved in  considerable  quantity  and  if  it  is  done  at  a  time  when  soil  and 
tree  conditions  do  not  stimulate  later  growth  the  same  season,  there  is 
not  only  an  immediate  reduction  in  size  but  reserves  for  the  following 
season  are  depleted  and  growth  the  next  year  will  be  correspondingly 
restricted.  Summer  pruning  under  such  conditions  has  a  distinct 
dwarfing  influence. 

In  conclusion,  then,  it  may  be  stated  that  summer  pruning  does  not 
necessarily  have  either  a  dwarfing  or  an  invigorating  influence.  It 
may  have  the  one  or  the  other,  depending  on  the  severity,  kind  and 
time  of  pruning  (as  related  to  the  state  of  development  of  the  plant, 
rather  than  to  the  exact  date  on  which  the  pruning  may  be  done). 
Environmental  conditions  also,  particularly  nutrient  supply,  soil  moisture 
and  light,  influence  greatly  the  nature  of  the  response  from  summer 
pruning.  Consequently  it  should  be  employed  as  an  orchard  practice 
only  when  due  consideration  is  given  the  several  factors  on  which  its 
results  depend.  The  amateur  or  the  careless  grower  cannot  use  it  safely. 
The  careful  student  of  fruit  growing  can  often  employ  it  with  reasonable 


444  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

certainty  of  the  results  and  frequently  will  find  it  of  great  value.  The 
results  attending  summer  pruning  in  some  of  the  best  managed  cane 
fruit  plantations  furnish  ample  evidence  to  this  effect. 

Influence  on  Production. — The  grower,  however,  is  interested  par- 
ticularly in  knowing  whether  or  not  certain  specific  objects  can  be  accom- 
plished— or  accomplished  more  readily — by  doing  the  work  at  one  season 
rather  than  at  another.  This  really  is  the  question  leading  to  most  of 
the  discussion  over  summer  pruning. 

The  opinion  receiving  general  acceptance  is  expressed  in  the  proverb, 
"prune  in  winter  for  wood  and  in  summer  for  fruit."  Quintinye^^ 
states  that  summer  pruning  leads  to  the  formation  of  fruit  buds  for  the 
following  crop.  Hovey,^^  referring  particularly  to  the  apple  and  pear, 
states  that  it  leads  to  the  formation  of  fruit  spurs  and  thus  indirectly 
aids  in  fruit  production.  Quinn^*  recommends  pinching  back  in  summer 
to  promote  fruitfulness  in  the  pear  and  Barry'^  recommends  this  practice 
even  more  generally  for  the  same  purpose.  Waugh^^  states  that  summer 
pruning  tends  to  promote  fruit-bud  formation.  Cole,^^  Downing^^  and 
many  others  recommend  summer  pruning  in  preference  to  winter  pruning, 
but  because  wounds  made  at  that  time  heal  more  readily  than  those 
made  at  other  seasons.  On  the  other  hand  Pearson^''  states  that  summer 
pruning  may  either  promote  or  repress  fruitfulness,  depending  on  how 
it  is  done.  The  general  idea  is  that  fruitfulness  is  promoted  by  summer 
pruning  through  checking  growth  or  weakening  the  plant. 

Though  the  majority  of  the  opinions  just  cited  are  from  American  writers, 
it  should  perhaps  be  stated  that  it  is  in  European  countries  that  the  practice  is 
most  commonly  employed  and  that  it  is  in  those  countries  that  it  is  generally 
believed  to  be  of  particular  value  in  promoting  fruitfulness.  In  America  there 
is  a  much  greater  diversity  of  opinion.  Much  of  the  apparent  difference  in 
results  attending  summer  pruning  in  this  country  and  in  Europe  is  to  be  explained 
through  the  difference  in  the  methods  employed.  The  growers  of  this  country 
mean  by  the  term  summer  pruning  a  pruning  similar  in  kind  and  in  amount  to 
that  ordinarily  done  during  the  dormant  season.  On  the  other  hand,  summer 
pruning  to  the  European  fruit  grower  means  something  entirely  different — for 
the  most  pai't  a  pinching  or  at  least  a  pruning  that  can  be  done  largely  "with 
the  thumb  and  forefinger."  This  type  of  pruning  is  employed  in  America  neither 
in  summer  nor  in  winter.  As  explained  later  under  Pinching  the  practice  of 
summer  pruning  commonly  employed  in  Europe  is  hardly  applicable  here  be- 
cause of  economic  considerations  and  consequently  the  extensive  European 
literature  on  summer  pruning  is  only  of  incidental  interest  to  most  American 
fruit  growers. 

In  the  section  on  Nutrition,  data  are  presented  showing  that  vigor 
of  growth  and  productiveness  are  not  necessarily  antagonistic  qualities. 
Indeed,  the  largest  yields  are  always  obtained  from  rather  vigorous  plants. 
The  belief  that  increased  fruitfulness  should  follow  summer  pruning  as 


PRUNING— THE  SEASON 


445 


generally  practiced  in  America,  is  therefore  based  on  two  assumptions, 
both  of  which  are  fundamentally  wrong.  This  is  shown  by  some  of 
the  more  recent  investigations  in  this  particular  field — notably  those 
in  Virginia,  1^  West  Virginia'  and  Utah.^'  All  these  showed  decreased 
production  of  flower  clusters  or  decreased  yields  of  fruit  following  the 
summer  pruning  of  young  trees  just  coming  into  bearing  or  with  their 
bearing  habits  not  yet  well  established  and  all  report  an  accompanying 
decrease  in  vegetative  growth.  In  one  of  the  West  Virginia  experi- 
ments the  yield  of  the  summer  pruned  trees  averaged  barely  a  third  of 
the  yield  from  those  receiving  winter  pruning.  On  the  other  hand 
Bedford  and  Pickering^  in  one  series  of  experiments  found  flower-bud 
formation  following  summer  pruning  greater  by  13  to  41  per  cent,  than 
following  winter  pruning,  depending  on  the  time  of  operation.  Alderman 
and  Auchter,'  who  found  summer  pruning  a  considerable  check  to  fruit 
production  in  apple  trees  just  coming  into  bearing,  report  no  such  general 
influence  on  mature  trees.  Table  16  summarizes  the  yields  obtained  in 
Idaho  over  a  7-year  period  from  winter  and  from  summer  pruned  plots. 
In  every  variety  under  trial  summer  pruning  resulted  in  an  increased 
yield. 

Table  16. — Average   Yields  in   Pounds  per  Tree  From  Winter  and  yuMMER- 
PRUNED  Trees 

{After  Vincent'^^) 


Variety 


Pruning 


1910,          1911, 
pounds     pounds 


1912, 
pounds 


1913, 
pounds 


1914, 
pounds 


1915, 
pounds 


1916, 
pounds 


Total, 
pounds 


Jonathan. . .  . 

Winter 

Jonathan. . .  . 

Summer 

Rome 

Winter 

Rome 

Summer 

Grimes 

Winter 

Grimes 

Summer 

Wagener .... 

Winter 

Wagener .... 

Summer 

29.0 
33.9 
13.9 
13.9 
13.2 
20.0 
29.0 
.54 .  3 


95.5 
95.5 
52.5 
58.5 
85.1 
99.5 
67.0 
123.2 


127.8 
144.3 
58.8 
85.0 
101.6 
195.5 
22.0 
50.8 


257.4 
252.1 
76.8 
80.0 

128.7 
88.5 
83.7 

1.59.0 


50.3 
51.7 
18.7 
23.0 
102.1 
155.  6 
6.2 
27.2 


2.39.  4 
272.1 
105.7 
160.4 
197.3 
108.3 
177.4 
215.5 


834.7 
870.9 
391.6 
450.8 
689.0 
738.4 
402.5 
689.4 


In  commenting  on  these  increases  Vincent^^  says:  "If  the  entire  orchard  had 
been  summer-pruned  there  would  have  been  an  increase  per  acre  during  the  7 
years  as  follows:  Jonathan,  30.02  boxes  or  an  increase  of  4.28  boxes  per  year; 
Rome,  49.7  boxes,  or  an  increase  of  7.1  boxes  per  year;  Grimes,  50.6  boxes  or  an 
increase  of  6.07  boxes,  per  year;  Wagener,  240.9  boxes  or  an  increase  of  34.4 
boxes  per  year.  Summer  pruning  therefore  has  increased  crop  production  on  all 
the  plats  and  quite  substantially  on  the  Wagener." 

In  neither  the  mature  West  Virginia  trees  nor  the  Idaho  trees  was 
summer  pruning  attended  by  an  appreciably  decreased  vegetative 
growth. 


446  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

At  first  glance  these  records  of  yields  from  summer  and  winter  pruned 
trees  seem  contradictory.  As  is  the  case  with  the  corresponding  records 
of  shoot  growth,  however,  they  can  be  reconciled.  It  has  been  pointed 
out  that  fruit  production  depends  on  (1)  the  formation  of  fruit-producing 
wood  and  (2)  on  the  proper  functioning  of  that  wood.  Furthermore, 
different  kinds  of  fruits  have  quite  unlike  fruiting  habits  and  the  processes 
culminating  in  fruit  production  may  be  quite  different  in  one  from  those 
in  another.  The  effect  of  summer  pruning  on  fruitfulness,  therefore, 
is  not  a  simple  question,  but  rather  a  series  of  questions  each  of  which 
must  be  answered  in  turn. 

Among  the  major  aspects  of  the  summer  pruning  problem  may  be 
stated  the  following:  (1)  The  concentrating  effects  of  different  kinds  and 
amounts  of  pruning  at  various  times  during  the  growing  season,  (2) 
The  relation  of  diverse  summer  pruning  treatments  to  shoot  growth 
both  of  the  current  and  of  the  following  season.  (3)  The  influence  on  new 
spur  formation.  (4)  The  effect  on  fruit  bud  formation — on  spurs  and 
on  shoots.  (5)  The  relation  to  the  intake  of  nutrients  and  to  the  manu- 
facture, translocation,  storage  and  utilization  of  elaborated  foods.  (6) 
The  influence  on  color  and  size  of  fruit.  These  questions  are  not  entirely 
distinct;  they  are  inter-related  and  inter-dependent.  Since  few  data  are 
available  concerning  some  of  them,  any  discussion  at  this  time  must  of 
necessity  be  incomplete.  It  is  attempted  here  on  a  few  aspects  only  of 
the  general  problem,  those  which  have  more  or  less  immediate  practical 
bearing  and  on  which  the  evidence  seems  reliable. 

Summer  Pruning  to  Develop  Framework. — Data  have  been  presented 
concerning  the  influences  of  summer  pruning  on  vegetative  growth  in 
general  and  on  new  shoot  formation  in  particular.  No  further  attention 
is  devoted  here  to  this  problem  except  to  indicate  a  rather  special  use 
of  early  summer  pruning  in  developing  the  framework  of  young,  strong, 
vigorously  growing  trees. 

Trees  of  many  kinds  growing  under  favorable  conditions  often  develop 
shoots  23^^  or  3  feet — and  sometimes  more — in  length  during  their  second, 
third  and  fourth  seasons  in  the  orchard.  Occasionally  they  make  such 
growth  their  first  season  and  shoots  of  this  character  are  not  at  all 
uncommon  as  the  trees  grow  older.  Ordinarily  most  of  this  shoot  growth 
is  cut  away  in  the  annual  dormant  season  pruning,  some  being  taken  out 
entirely  and  the  terminal  half  or  even  three-fourths  of  each  remaining 
shoot  generally  being  removed.  This  heavy  cutting  back  is  necessary 
for  securing  a  strong  framework  and  a  compact  type  of  growth.  The 
question  naturally  arises  whether  these  trees  can  be  pruned  in  mid- 
summer shortly  after  the  shoots  have  attained  a  length  equaling  that  to 
which  they  would  be  cut  back  at  the  usual  winter  pruning.  This  would 
then  be  followed  by  the  production  of  secondary  lateral  shoots,  many  of 
which  could  be  saved  with  little  or  no  heading  back  at  the  following 


PRUNING— THE  SEASON  447 

winter  pruning.  In  this  way  two  steps  in  the  construction  of  the  franie- 
work  of  the  tree  would  be  taken  in  one  season  and  theoretically  a  year 
would  be  saved  in  growing  the  tree  to  producing  size  and  in  bringing  it 
into  bearing.  This  type  of  summer  pruning,  which  includes  both  thin- 
ning and  heading  early  in  the  summer  (about  July  1)  was  studied  with 
apples  in  Oregon.-^  Though  such  varieties  as  Jonathan,  Grimes,  Yellow 
Newtown  and  Wagener  summer  pruned  in  this  way  did  not  make  the 
equivalent  of  two  seasons'  ordinary  growth  in  one  summer,  three  success- 
ive years  of  such  treatment  resulted  in  trees  comparable  in  size,  fruit 
spur  development  and  productiveness  to  winter  pruned  trees  a  year 
older.  In  other  words  a  j^ear  had  been  gained  in  developing  their  frame- 
work and  in  bringing  them  into  bearing.  Observation  led  to  the  belief 
that  this  method  of  pruning  is  equally  valuable  in  forcing  the  early  de- 
velopment of  both  pears  and  sweet  cherries.  This  special  pruning  prac- 
tice is  desirable  with  young  trees  only  under  favorable  growing  conditions 
when  they  are  making  new  shoots  at  least  2}^  feet  in  length  and  where 
the  growing  season  is  long  enough  to  permit  a  proper  maturity  of  the 
late  secondary  shoots. 

Summer  Pruning  as  a  Conservation  Measure. — It  has  been  stated 
before  that  the  removal  of  any  living  portion  of  the  top  of  a  plant  at  any 
time  deprives  the  plant  of  a  certain  amount  of  elaborated  food  material. 
This  is  true  particularly  of  pruning  in  summer  when  the  storage  tissues 
have  been  depleted  for  the  building  of  new  structures.  However,  the 
removal  of  any  portion  of  the  top  reduces  somewhat  the  demand  on  the 
root  system  for  nutrients  and  moisture;  under  certain  conditions  this 
reduction  may  enable  the  roots  to  supply  the  remaining  parts  with 
amounts  nearer  their  requirements  for  growth.  In  this  way  pruning 
can  be  said  to  have  a  stimulating  influence.  In  other  words,  it  may  be 
regarded  as  a  conservation  measure,  making  given  amounts  of  moisture 
and  nutrients  go  further;  because  these  larger  amounts  of  materials  are 
available,  certain  parts  may  manufacture  and  store  more  elaborated 
foods  than  they  could  otherwise.  This  may  be  considered  a  concentra- 
tion effect.  The  concentration  is  limited  to  certain  parts  and  in  some 
instances  other  parts  may  suffer  and  perhaps  the  plant  as  a  whole  may  be 
weakened.  Apparently  one  of  the  more  important  objects  that  may  be 
accomplished  by  pruning  during  the  growing  season  is  due  to  this  in- 
fluence. 

This  effect  of  summer  pruning  depends  on  many  factors.  Among  the 
more  important  are:  (1)  the  severity  of  the  pruning,  (2)  its  kind,  (3)  the 
exact  stage  of  development  of  the  plant  at  the  time  the  pruning  is  done 
and  (4)  the  soil  conditions  before,  at  the  time  of  and  after  the  operation. 

Independent  of  the  other  factors,  it  is  evident  that,  within  certain 
limits,  the  more  severe  the  pruning  the  greater  will  be  its  effect  in  diverting 
into  the  remaining  parts  nutrients  and  moisture.     However,  a  point  is 


448  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

always  reached,  unless  the  operation  is  performed  shortly  before  the  begin- 
ning of  the  dormant  season,  when  an  increase  in  the  severity  of  the  pruning 
results  in  forcing  into  growth  buds  that  otherwise  would  remain  dormant 
until  the  following  spring.  At  this  point  its  general  effect  changes  from 
conservation  to  dissipation  since  the  new  tissues  demand  not  only  soil 
nutrients  and  moisture  but  elaborated  foods  as  well.  The  branches, 
canes  or  shoots  remaining  and  perhaps  the  whole  plant,  are  left  weaker 
in  that  they  are  likely  to  enter  the  dormant  season  less  richly  supplied 
with  elaborated  food  materials.  In  general  the  conservation  effects  of 
any  pruning  cease  when  it  promotes  greater  utilization  of  reserve  foods 
in  the  building  of  new  tissue.  Were  these  effects  (that  is,  the  ratio  that 
they  bear  to  the  total  effects)  of  summer  pruning  plotted  in  a  curve  as 
they  vary  with  the  severity  of  the  pruning  this  curve  would  start  close  to 
the  100  per  cent  value  with  very  light  pruning  and  fall  steadily  with  each 
increase  in  severity  until  the  zero  point  is  reached.  Furthermore  this 
general  situation  would  obtain  regardless  of  the  kind  of  the  pruning  or  of 
the  exact  time  of  the  operation,  though  in  no  two  cases  could  the  curves 
be  expected  to  be  exactly  parallel. 

Closely  related  to  the  stimulating  effect  of  varying  amounts  of  summer 
pruning  is  the  influence  of  the  stage  of  seasonal  development  at  which  it 
is  done.  In  general  a  very  early  summer  pruning,  particularly  if  it 
consists  in  thinning  out,  is  most  effective  in  diverting  the  energies  of 
the  plant  into  other  developing  or  already  developed  tissues.  It  may 
lead  to  greater  elongation  of  shoots,  to  shorter  internodes  and  more 
leaves,  possibly  to  the  formation  of  side  branches  or  to  several  other 
growth  responses  or  it  may  simply  result  in  a  more  efficient  functioning 
of  the  remaining  tissues.  This,  for  instance,  is  the  general  effect  of  the 
prompt  removal  of  watersprouts,  suckers  or  other  shoots  just  as  they  are 
starting.  If  the  pruning  is  done  a  little  later,  during  the  period  of  most 
rapid  vegetative  growth,  it  may  have  a  concentrating  effect  (that  is, 
lead  to  the  greater  accumulation  of  elaborated  foods)  or  it  may  have  the 
opposite  effect  and  force  out  a  crop  of  secondary  shoots,  the  kind  of  the 
response  varying  with  the  severity  and  kind  of  the  pruning.  Pruning 
late  in  the  growing  season,  if  not  too  severe,  is  almost  sure  to  have  a 
concentrating  effect  (for  the  particular  parts  affected),  since  no  new 
growth  will  take  place  to  utilize  the  stored  foods  and  there  will  be  still 
further  accumulations  resulting  from  the  increased  supply  of  nutrients 
and  of  light. 

Of  the  two  kinds  of  summer  pruning,  thinning  out  generally  has  a 
much  greater  concentrating  effect  than  heading  back.  The  latter 
practice,  unless  it  consists  in  a  mere  pinching  out  of  the  terminals  or 
unless  it  comes  very  late  in  the  season,  results  immediately  in  the  forma- 
tion of  numerous  secondary  lateral  branches.  Their  development 
consumes  food  materials  that  have  been,  or  are  being,  manufactured  and 


PRUNING—THE  SEASON  449 

results  in  a  shading  of  leaves  lower  in  the  tree  and  possibly  in  reduced 
rates  of  photosynthesis  and  of  food  manufacture.  However,  a  light 
heading  back  or  pinching  of  the  terminals  of  the  grape  early  in  the  season, 
thus  temporarily  checking  new  shoot  growth,  is  said  to  aid  materially 
the  setting  of  fruit  in  certain  varieties.^  This  is  a  concentration  effect, 
though  the  practice  is  of  special  rather  than  general  application.  On  the 
other  hand  thinning  out  has  no  such  tendency  to  encourage  the  develop- 
ment of  secondary;  shoots  certainly  they  are  not  formed  to  anything 
like  the  same  extent  as  with  summer  heading.  More  light  is  admitted  to 
the  interior  of  the  plant  which  is  better  supplied  with  nutrients  and 
moisture  and  the  result  is  an  increased  accumulation  of  elaborated  foods. 
The  results  attending  a  well  distributed  thinning  of  the  shoots  and  smaller 
branches  would  be  more  pronounced  in  this  direction  than  those  following 
a  coarse  or  bulk  thinning. 

When  soil  conditions,  particularly^  moisture  and  nutrient  supply, 
encourage  new  vegetative  growth,  summer  pnming  is  much  less  likely  to 
exert  concentrating  effects  than  it  is  when  less  moisture  and  less  nitrogen 
are  available.  Indeed  its  influence  may  be  the  reverse,  particularly  if  the 
summer  pruning  has  been  mainly  heading  back.  Generally  speaking,  it  is 
easier  to  secure  the  concentration  effects  of  summer  pruning  when  the 
available  soil  moisture  and  nitrates  are  not  too  high  and  when  atmospheric 
conditions  favor  a  high  transpiration  rate.  These,  it  will  be  recognized, 
are  the  conditions  under  which  it  has  been  suggested  by  Chandler'"  that 
summer  pruning  can  be  employed  advantageously  as  a  moisture- 
conserving  measure  to  prevent  the  wilting  of  partly  grown  fruits  on 
heavily  laden  and  vigorously  growing  trees.  The  influence  of  certain 
summer  pruning  practices  on  the  formation  of  fruit  buds,  discussed  a 
little  later,  is  probably  due  to  their  concentrating  effect. 

In  a  general  way  it  may  be  stated  that  summer  pruning  is  often 
very  useful  because  of  its  influence  in  diverting  the  energies  of  the  plant 
into  other  channels.  In  the  average  plant  most  of  the  watersprouts  and 
suckers  (except  those  used  for  renewal  purposes)  are  worse  than  useless. 
They  dissipate-  energies  and  yield  little  in  return.  Their  prompt 
removal  is  a  conservation  measure  and  is  particularly  important  in 
certain  fruits  like  the  grape  and  in  nearly  all  young  trees.  The  longer 
the  delay  in  cutting  them  out  the  less  is  gained  by  removing  them. 
Practically  the  same  statement  holds  for  the  early  summer  removal  of  a 
portion  of  the  barren  shoots  in  the  grape  and  certain  other  plants. 
Midsummer  or  late  summer  pruning  may  be  desirable  occasionally,  in 
so  far  as  it  reduces  transpiration  losses  and  indirectly  aids  in  the  sizing 
and  coloration  of  the  fruit. 

It  should  be  reiterated  that  the  concentrating  effect  of  pruning  does 
not  necessarily  invigorate  the  plant  as  a  whole.  In  fact  it  may  have 
exactly  the  opposite  influence,  though  certain  parts  are  favored  by  the 


450  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

process.  Thus  a  heavily  laden  peach  tree  pruned  in  late  July  as  a  protec- 
tion against  drought  is  probably  weakened  by  the  operation  and  may 
show  the  effects  in  the  new  growth  put  out  the  following  spring,  though 
the  pruning  operation  enabled  the  fruit  to  mature  properly.  The 
situation  is  simply  another  aspect  of  a  problem  constantly  encountered 
in  pruning  practice — that  of  subordinating  or  even  eliminating  one  part 
in  the  interest  of  another. 

Influence  on  New  Spur  Formation. — The  influence  of  summer  pruning 
on  new  shoot  formation  and  consequently  on  the  fruit-producing  wood 
in  plants  bearing  on  shoots  or  canes  has  been  discussed.  There 
remains  consideration  of  its  influence  on  new  spur  formation.  Spurs  are 
generally  formed  from  lateral  buds  on  the  long  growths  of  the  current 
or  of  the  preceding  season.  Only  a  certain  percentage  of  these  grow  out 
into  spurs,  the  number  depending  on  many  factors,  among  the  more 
important  of  which  are  (1)  the  supply  of  nutrients  and  elaborated  food 
materials  available  for  their  growth  and  (2)  the  relative  stage  of  develop- 
ment or  the  size  of  the  buds  themselves.  The  influence  of  summer 
pruning  on  the  supply  of  available  foods  has  just  been  considered  under 
the  head  of  Concentration;  consequently  that  aspect  of  the  question 
need  not  be  discussed  further. 

Observation  shows  that  in  almost  all  species  there  are  considerable 
differences  in  the  size  of  the  lateral  buds  on  the  long  growths  or  shoots. 
Usually  those  on  the  basal  portion  are  small  and  inclined  to  remain 
dormant  unless  stimulated  into  growth  by  some  special  pruning  or 
other  treatment;  the  buds  on  the  median  and  terminal  portions  of  the 
shoot  are  better  developed  and  grow  out  readily,  to  form  either  shoots  or 
spurs.  Apparently  their  greater  size  and  development  is  due  largely  to 
the  better  light  supply  and  to  the  more  favorable  location  for  food  manu- 
facture, of  the  leaves  that  subtended  them.  Obviously  almost  any 
pruning  and  particularly  any  summer  pruning  will  influence  the  amount 
of  light  reaching  the  leaves  on  the  remaining  shoots.  In  many  fruits  sum- 
mer heading  back,  unless  very  light  and  done  comparatively  late  in 
the  season,  encourages  the  formation  of  laterals  or  secondary  shoots  and 
consequently  produces  poorer  conditions  for  photosynthesis  in  the  lower 
parts  of  the  plant.  At  the  same  time,  as  shown  later  under  Pinching, 
it  results  in  thickening  the  bark  on  the  lower  portion  of  the  shoot  and 
therefore  in  different  food  storage  conditions  that  are  associated  with  the 
change  in  the  relative  proportions  of  the  several  tissues.  These  effects 
may  outweigh  in  importance  those  occasioned  by  greater  shading.  There 
is  reason  to  believe  that  in  at  least  some  fruits  summer  heading  acts  as  a 
stimulus  to  fruit-bud  formation  on  the  current  season's  shoots.  On  the 
other  hand  thinning  out  admits  more  light  to  the  leaves  on  the  lower 
part  of  the  shoots  and  thus  encourages  the  elaboration  of  foods  and  the 
formation   of   larger   and   stronger   buds.     Summer   thinning   therefore 


PRUNING— THE  SEASON  451 

tends  to  encourage  fruit-spur  formation.  This  is  in  a  sense  another 
concentrating  effect  of  summer  pruning.  It  is  evident  from  what  has 
been  said  that  the  earlier  in  the  season  the  pruning  is  done  the  greater  is 
its  influence  in  this  direction. 

Gardner 21  has  reported  that  in  young  apple  trees  not  yet  in  bearing 
greatly  increased  fruit-spur  formation  follows  early  summer  pruning 
in  addition  to  winter  pruning.  This  is  not  so  much  because  of  the  better 
spur  production  from  the  buds  left  on  the  primary  shoots  after  the 
summer  pruning  as  because  after  the  pruning  many  secondary  shoots  are 
produced  on  which  the  buds  grow  out  readily  to  form  new  spurs  the 
following  season.  In  apples  nearly  all  the  buds  on  these  late  summer 
secondary  shoots  enter  the  winter  in  practically  the  same  condition  as,  and 
are  comparable  in  every  way  to,  the  buds  on  the  median  and  terminal  por- 
tions of  the  primary  shoots.  ^^  j^  f^g^  ^^e  of  the  most  useful  purposes 
served  by  the  early  summer  pruning  of  young  vigorously  growing  spur 
bearing  trees  Hke  the  apple  is  to  increase  the  number  of  spurs  over  that 
secured  by  winter  pruning  alone.  It  is  worthy  of  mention  that  spurs 
developing  from  these  secondary  late  summer  shoots  are  as  a  rule 
especially  strong,  vigorous  and  likely  to  produce  fruit  buds. 

Influence  on  Fruit-hud  Formation. — In  the  section  on  Nutrition 
it  is  shown  that,  in  all  cases  studied,  fruit-bud  differentiation  is  associated 
with  carbohydrate  accumulation  in  the  immediate  vicinity  of  the  buds 
concerned.  The  work  of  Magness^^  on  young  apple  trees  indicates  that 
this  accumulation  takes  place  principally  where  there  is  the  greatest 
effective  leaf  area.  In  other  words,  within  certain  limits  those  spurs 
that  have  the  largest  and  best  lighted  leaves  accumulate  the  largest 
reserves  of  carbohydrates  and  differentiate  the  most  fruit  buds.  He 
found  that  by  partial  or  complete  defoliation  of  spurs  well  supplied  with 
leaves,  fruit-bud  formation  on  these  spurs  could  be  entirely  prevented, 
even  though  adjacent  spurs  retaining  their  full  complements  of  leaves 
formed  fruit  buds  freely.  Similarly  he  found  that  the  formation  of 
lateral  fruit  buds  took  place  only  in  the  axils  of  good  sized,  well  lighted 
leaves. 

Magness^^  summarizes  his  results  as  follows:  "Fruit-bud  initiation  will  not 
take  place,  and  fruit  buds  will  not  form  in  most  varieties  in  the  absence  of  a  fair 
amount  of  leaf  area  in  the  tree. 

"Food  material  stored  in  the  tree  through  the  dormant  season  is  apparently 
stored  largely  in  the  tissue  adjacent  to  the  leaves  in  which  it  was  manufactured. 
This  is  shown  by  the  fact  that  the  defoliated  portion  does  not  develop  as  strongly 
and  well  during  the  spring  following  the  treatment,  as  does  the  undefoliated 
portion. 

"Leaf  area  in  one  part  of  the  tree  will  usually  not  supply  food  material  to 
the  buds  in  another  part  to  the  extent  necessary  to  cause  them  to  become  fruit 
buds.     DefoHating  one-half  of  a  tree  has  Uttle  influence  upon  the  undefoliated 


452  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

portion,  but  that  part  which  is  defoliated  functions  as  it  would  if  all  the  leaves 
had  been  removed  from  the  whole  tree. 

"Removing  the  same  number  of  leaves,  without  any  pruning,  has  practically 
the  same  effect  upon  the  fruit-bud  formation  for  the  immediate  year  following 
that  a  summer  pruning,  removing  leaves  from  the  same  position,  would  have. 

"Buds  on  1-year  wood,  in  areas  from  which  the  leaves  have  been  removed 
are  slower  in  starting  out  into  growth,  and  make  a  weaker  growth  the  following 
spring  than  do  other  buds  on  the  same  shoots  not  defoliated.  This  is  more 
noticeable  in  some  varieties  than  in  others. 

"One  shoot  seems  to  be  very  largely  independent  of  other  shoots  about  it  so 
far  as  fruit-bud  formation  is  concerned.  It  is  apparently  largely  dependent  upon 
its  own  leaves  for  nourishment. 

"Removing  leaves  from  individual  spurs  tends  to  prevent  the  formation  of 
fruit  buds  upon  those  spurs,  although  it  does  not  entirely  check  the  development 
of  flower  parts. 

"On  those  spurs  which  form  fruit  buds,  notwithstanding  defoliation,  the 
blossoms  are,  on  the  average,  considerably  later  in  opening  in  the  spring. 

"Axillary  buds  of  the  Wagener  seem  to  be  almost  entirely  dependent  upon 
the  immediate  subtending  leaf  for  the  carbohydrate  supply  with  which  they  are 
nourished.  Removing  the  subtending  leaf  entirely  prevents  fruit-bud  formation. 
Buds  so  treated  either  remained  entirely  dormant  during  the  following  growing 
season  or  pushed  out  into  very  weak  growth.  Very  few  of  them  showed  a 
development  approaching  normal." 

Magness'  work  may  explain  incidentally  why  the  basal  portions  of 
shoots  often  produce  relatively  fewer  fruit  buds  than  the  median  and 
terminal  portions.  The  basal  portions  are  poorly  lighted  and,  assuming 
leaves  of  equal  size,  they  would  manufacture  smaller  amounts  of  elabo- 
rated foods.  Neither  spurs  nor  shoots  can  be  expected  to  differentiate 
fruit  buds  freely  if  they  are  heavily  shaded.  Summer  pruning,  however, 
naay  admit  more  light  both  to  the  spurs  and  to  the  basal  portions  of 
the  shoots  at  the  same  time  it  concentrates  the  supply  of  nutrients. 
This  direct  influence  on  the  factors  associated  with  fruit-bud  formation 
could  hardly  help  but  influence  more  or  less  directly  the  relative  number 
of  fruit  buds.  Obviously  early  summer  pruning  comprising  thinning 
out  instead  of  heading  back  would  have  the  greatest  influence  of  this 
kind.  No  pruning  practice  after  fruit-bud  formation  for  the  season 
is  completed  could  conceivably  have  any  influence  in  this  direction  and 
heading  back  with  the  formation  of  many  secondary  lateral  branches 
would  cause  still  heavier  shading  and  reduce  rather  than  increase  fruit- 
bud  formation.  Doubtless  many  of  the  cases  in  which  summer  pruning 
has  failed  to  produce  an  increased  number  of  fruit  buds  have  been  due 
to  its  consisting  mainly  in  heading  back  or  being  done  too  late  to 
have  any  important  influence  in  this  direction.  Experience  shows  that 
a  light  or  moderate  early  summer  thinning  of  the  shoots  of  those  trees 
such  as  the  peach  that  bear  laterally  on  shoots  aids  greatly  in  the  forma- 


PRUNING—THE  SEASON  453 

tion  of  fruit  buds  on  the  basal  and  median  portions  of  those  shoots. 
Though  such  summer  pruning  may  not  result  in  any  considerable  increase 
in  the  total  number  of  fruit  buds,  it  does  favor  fruit-bud  formation 
in  more  desirable  places  and  is  well  worth  while. 

Influence  on  Fruit  Color. — In  the  apple,  peach  and  certain  other 
fruits  the  development  of  the  red  colors  in  the  skin  of  the  fruit  depends 
mainly  on  sunlight.  With  those  fruits  summer  pruning  naturally 
influences  their  coloration,  particularly  if  the  pruning  consists  mainly 
in  thinning  out.  Vincent*''  reports  that  summer,  as  compared  with 
winter,  pruning  the  apple  in  Idaho  resulted  in  an  increase  of  33  per  cent, 
of  extra  fancy  apples  in  Jonathan,  32  per  cent  in  Rome  and  5  per  cent 
in  Wagener,  the  grading  being  mainly  on  the  basis  of  standard  commercial 
color  requirements.  The  coloring  of  certain  other  fruits,  as  plums  and 
grapes,  does  not  depend  on  light  reaching  the  fruit  itself,  though  pig- 
ment formation  depends  on  carbohydrate  manufacture  in  near  by 
leaves.  Consequently  summer  pruning  is  of  less  direct  aid  in  the  colora- 
tion of  these  fruits.  Bioletti,^  however,  states  that  judicious  summer 
pruning  may  occasionally  favor  the  coloring  of  the  fruit  in  certain  grape 
varieties.  Presumably  this  influence  is  exercised  through  the  better 
lighting  of  the  foliage  near  the  fruit  clusters. 

Most  fruits  develop  their  color  late  in  the  growing  season  or  shortly 
before  ripening.  Consequently  summer  pruning  to  promote  a  better 
coloring  of  the  fruit  may  be  done  comparatively  late.  In  pruning  for 
this  purpose  caution  should  be  exercised;  too  severe  or  too  early  summer 
pruning  is  likely  to  result  in  more  or  less  sunburn  of  the  fruit. 

Summer  Pinching. — It  is  impossible  to  distinguish  clearly  between 
what  is  termed  pinching  and  what  is  usually  termed  topping  or  heading 
back.  The  difference  between  the  operations  is  siniplj'  in  the  maturity  of 
the  tissues  at  the  time  the  operation  is  performed  and  in  the  relative 
amount  of  new  growth  removed.  In  some  species,  as  for  example  the 
rambles,  pinching  leads  to  considerable  branching  of  the  pinched  shoots; 
in  many  others  it  may  be  attended  by  very  little  branching,  one  or  two  of 
the  subterminal  buds  promptly  growing  out  to  replace  the  leader.  Conse- 
quently its  general  effect  may  be  concentration  or  dissipation  and  dilution, 
depending  on  the  species  and  on  conditions.  Summer  pinching  has  been 
much  used  in  European  fruit  growing  and  in  the  growing  of  fruits  under 
glass.  In  this  country  it  has  been  used  mainly  with  the  brambles  and  with 
grapes,  though  occasionally  it  is  helpful  in  checking  or  directing  growth 
in  some  of  the  other  fruits. 

There  seems  to  be  much  difference  of  opinion  among  growers  and 
investigators  as  to  the  wisdom  of  summer  pinching  of  brambles.  Both 
satisfactory  and  unsatisfactory  results  have  been  reported.  Apparently 
much  depends  on  the  time  of  the  operation;  furthermore  varieties  respond 
quite  differently  to  the  same  treatment.     Macoun^'  has  reported  that  at 


454  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Ottawa,  Canada,  red  raspberries  pinched  back  in  early  summer  and  thus 
forced  to  branch,  generally  yield  less  than  untreated  plants.  Since 
Kenyon,  Loudon,  King,  Hansell  and  Miller  (red  raspberries)  do  not  branch 
freely,  they  should  never  be  summer  pinched.*^  The  main  advantage 
claimed  for  summer  pinching  is  that  it  results  in  a  lower,  more  compact, 
bushy  plant  with  mechanically  stronger  canes  than  those  that  are  un- 
headed  and  unbranched.  Consequently  they  hold  up  their  fruit  better 
and  require  less  trellising.  Dewberries  which  usually  require  trellising 
are  seldom  summer  pinched.  It  is  generally  agreed  that  if  raspberries  or 
blackberries  are  to  be  summer  pinched  the  operation  should  be  performed 
early,  when  the  shoots  are  only  18  to  24  inches  high  or  perhaps  even 
before  this.^  Pinching  higher  or  cutting  back  to  this  point  at  a  later  date 
is  likely  to  result  in  weak,  late-maturing  laterals  that  are  especially  sub- 
ject to  winter  injury  and  are  less  likely  to  give  rise  the  following  year  to 
good  fruiting  shoots.  Blackberries  and  black  raspberries  generally 
respond  better  than  red  raspberries  to  summer  pinching.  Pinching  the 
ends  of  the  growing  shoots  just  before  blossoming  has  been  stated 
to  aid  sometimes  in  the  setting  of  fruit  in  the  grape;  it  is  thus  a  partial 
remedy  for  "coulure."^  Bioletti*'  mentions  pinching  as  sometimes  useful 
also  in  protecting  grapes  from  sunburn  by  causing  the  shoots,  through 
more  rapid  lignification,  to  remain  more  upright  and  to  furnish  more  shade 
for  the  fruit  clusters.  But  little  evidence  is  available  concerning  the 
influence  of  summer  pinching  on  fruit-bud  formation  in  the  grape  and  at 
present  it  cannot  be  recommended  confidently  for  any  effect  of  this  sort. 
The  early  and  repeated  pinching  back  of  shoots  of  the  apple  and  pear 
to  stimulate  the  development  of  fruit  spurs  and  fruit  buds  has  been  dis- 
cussed freely.  Thomas^^  states  that  "  by  pinching  off  the  soft  ends  of  the 
side-shoots  after  they  have  made  a  few  inches  of  growth — the  sap  imme- 
diately accumulates,  and  the  young  buds  upon  the  remainder  of  these 
shoots,  which  otherwise  would  produce  leaves,  are  gradually  changed  into 
fruit  buds.  To  prevent  the  breaking  of  these  buds  into  new  shoots  by  too 
great  an  accumulation  of  the  sap,  partial  outlet  is  left  for  its  escape 
through  the  leading  shoot  of  the  branch,  which  at  the  same  time  is  effect- 
ing the  desired  enlargement  of  the  tree.  ...  It  often  happens,  and  espe- 
cially when  the  pinching  is  done  too  early,  that  the  new  buds  send  out 
shoots  a  second  time  the  same  season.  When  this  occurs,  these  second 
shoots  are  to  be  pinched  in  the  same  manner  as  the  first,  but  shorter;  and 
third  ones,  should  they  start,  are  to  besimilarly  treated."  Barry, ^Rivers^^ 
and  others  recommend  the  same  treatment  for  the  same  purpose  and  these 
early  authorities  have  been  followed  by  many  later  writers.  Recently 
Ballard  and  Volck^"  in  California  have  shown  that,  by  two  or  three  repeated 
summer  pinchings,  fruit  spurs  bearing  fruit  buds  can  be  developed  from 
watersprouts  of  the  apple  in  one  season.  They  found  also  that  normal 
shoots  throughout  the  tree  respond  in  the  same  way  to  similar  treatment. 


PRUNING— THE  SEASON 


455 


Gaucher^s  recommends  early  summer  pinching  in  spurs  which  are  growing 
out  into  vegetative  shoots.  He  states  this  pinching  usually  stops  further 
growth  from  the  terminal  bud  and  forces  out  at  lower  points  on  the  spur 
lateral  buds  that  otherwise  would  remain  latent.  These  then  develop 
into  branch  spurs  that  often  form  fruit  buds  the  first  season.  If  a  single 
pinching  does  not  result  in  fruit-spur  and  fruit-bud  formation,  a  second 
pinching  is  recommended, 

Goumy^s  studied  the  influence  of  summer  pinching  on  the  subsequent 
development  of  bark  and  wood;  some  of  his  results  are  summarized  in 
Table  17.  Pinching  obviously  has  led  to  a  proportionally  greater 
development  of  the  bark.  Goumy  found  also  some  difference  between  the 
relative  amounts  of  bark  and  of  wood  in  the  spurs  on  the  year  old  growth 
of  pinched  and  unpinched  spurs.  The  determination  of  just  what  these 
differences  in  relative  amounts  of  bark  and  wood  signify  in  terms  of  nutri- 

Table  17. — Influence  of  Summer  Pinching  on  Relative  Thickness  of  Bark 
AND  Wood  in  the  Pinched  Shoot  of  the  Pear 

(After  Goumy^^) 


Tissue 

Shoot  not  pinched 

Shoot  pinched 

Pith 

2.3 
5.5 
2.25 

1.0 

2.2 
0.6 
1.6 
0.6 

2  8 

Wood                

3  7 

Bark 

Bark  tissues  in  particular: 

Epidermis 

Cortical  parenchyma                

3.4 

1.0 

4  4 

Sclerenchyma 

Cortex 

0.5 
3.0 

0.6 

tive  conditions  and  food  reserves  is  difficult,  but  presumably  they  favor 
fruit-bud  formation  in  the  pinched  shoots. 

However,  summer  pinching  has  been  practiced  frequently  for  the 
purpose  of  promoting  fruit  spur  and  fruit-bud  formation  and  has  not 
secured  the  expected  response.  In  general  it  may  be  stated  that,  though 
the  practice  may  produce  satisfactory  results  if  followed  properly  by  succes- 
sive pinching  of  secondary  and  tertiary  shoots,  the  amount  and  kind  of 
labor  involved  are  such  as  to  make  it  of  doubtful  value  in  the  commercial 
fruit  plantation  in  America.  When  trees  are  grown  as  standards  other 
measures  or  practices  that  are  available  will  call  forth  more  of  a  mass 
response  and  will  provide  at  much  less  expense  the  requisite  number  of 
fruit  spurs  and  fruit  buds. 

The  early  summer  pinching  of  shoots  in  young  trees  for  the  purpose 
of  subordinating  those  that  are  not  wanted  for  permanent  framework  is 
only  occasionally  employed  but  is  frequently  to  be  recommended.     In 


456  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

newly  planted  trees  the  buds  within  a  short  distance  from  the  ground 
often  start  to  grow.  Generally  the  resulting  shoots  are  promptly  rubbed 
off  or  they  are  pruned  away  after  they  have  been  allowed  to  grow  a  year. 
In  either  case  the  growth  of  the  upper  branches  is  very  likely  to  be  checked. 
If  these  lower  shoots  are  promptly  pinched  back  so  as  to  leave  three  or 
four  leaves  apiece  the  upper  shoots  are  not  checked  in  their  development, 
the  trunk  is  shaded  and  the  food  materials  that  their  leaves  manufacture 
will  be  of  considerable  value  in  promoting  a  vigorous  growth  the  following 
season,  after  which  they  can  be  removed.  Similarly  in  trees  that  have 
been  growing  in  the  orchard  for  1,  2  or  3  years,  are  formed  many  shoots 
that  ordinarily  are  removed  at  the  following  dormant-season  pruning. 
Their  growth  reduces  somewhat  the  development  of  those  desired  for  the 
permanent  framework.  Pinching  them  back  early  in  the  season  sup- 
presses them  and  the  nutrients  and  moisture  are  largely  diverted  into  other 
parts,  but  at  the  same  time  their  leaf  surface  serves  to  manufacture 
elaborated  foods  for  the  current  and  the  following  seasons. 

Summary. — On  the  whole  but  little  difference  is  likely  to  result  from 
pruning  at  different  times  during  the  dormant  season,  though  in  certain 
fruits  early  pruning  is  followed  by  earlier  foliation  in  the  spring.  This  is 
a  factor  of  commercial  importance  in  grape  culture.  Very  late  pruning 
generally  leads  to  more  bleeding  than  earlier  pruning.  Bleeding  from 
pruning  wounds  seldom  harms  the  plant. 

Summer  pruning  may  have  a  dwarfing  or  an  invigorating  influence 
(as  compared  with  a  corresponding  winter  pruning),  depending  on  its 
severity,  kind,  the  stage  of  development  of  the  plant  and  on  environ- 
mental conditions — particularly  nutrient  supply,  soil  moisture  and  light. 
A  light  summer  thinning  encourages  fruit-spur  formation  through  favor- 
ing the  development  of  larger  and  stronger  lateral  buds  from  which  spurs 
are  formed.  The  same  practice  promotes  fruit-bud  formation  also  if  the 
work  is  done  early  enough  in  the  season.  Heading  back  tends  to  stimu- 
late purely  vegetative  growth.  Judicious  summer  pruning  is  more  or 
less  a  conservation  measure.  This  applies  particularly  to  the  removal 
of  watersprouts  and  other  superfluous  growth.  In  very  strong  vigorously 
growing  trees  2  to  5  years  old  early  summer  pruning  results  in  encouraging 
a  late  secondary  growth  and  this  may  be  a  means  of  hastening  the  general 
development  of  the  tree  if  there  is  a  long  growing  season  and  other  condi- 
tions are  favorable.  A  light  summer  pruning  may  aid  materially  the 
coloration  of  fruit  in  certain  species. 

Summer  pinching  in  general  encourages  the  development  of  sec- 
ondary shoots.  This  is  often  desirable  in  the  culture  of  the  bramble 
fruits.  Pinching  may  be  used  also  to  subordinate  individual  shoots  and, 
in  the  spur-bearing  species,  it  may  result  in  their  developing  into  spurs. 
This  practice  is  of  doubtful  utility,  however,  in  the  culture  of  standard 
trees. 


CHAPTER  XXV 
PRUNING  WITH  SPECIAL  REFERENCE  TO  PARTICULAR  FRUITS 

In  a  preceding  chapter  were  discussed  some  of  the  more  important 
general  or  mass  effects  of  pruning.  •  Mention  was  made  also  of  the  more 
specific  influence  of  certain  practices  on  fruit-spur,  shoot  or  fruit-bud 
formation  in  particular  parts  of  the  tree,  though  this  concerned  the 
general  aspects  of  those  questions  rather  than  the  particular  applications 
presented  by  different  fruit  plants.  Another  chapter  attempts  to  explain 
in  some  detail  the  fruit  bearing  habits  of  the  more  connnon  fruits.  There 
remains  for  discussion  the  adaptation  of  pruning  practices  to  plants  hav- 
ing these  different  methods  of  bearing  so  that  maximum  annual  produc- 
tion may  be  obtained  along  with  the  form  of  tree  or  plant  most  conducive 
to  long  hfe  and  economy  in  production.  It  should  not  be  inferred, 
however,  that  all  fruit  plants  with  the  same  fruiting  habit  should  be 
pruned  alike.  Their  general  growing  habits,  that  is,  the  amount  and 
character  of  their  new  vegetative  growth,  may  be  quite  different  and 
necessitate  equally  diverse  pruning  treatments.  Though  the  Winter 
Nelis  pear  has  essentially  the  same  bearing  habit  as  the  Maiden  Blush 
apple,  the  two  must  be  pruned  quite  differently  because  they  are  so 
unlike  in  their  vegetative  growth  and  the  red  raspberry  with  essentially 
the  same  fruiting  habit  as  the  black  raspberry  should  be  pruned  more 
sevei'ely  because  of  its  great  tendency  to  sucker;  many  other  instances 
might  be  cited. 

Broadly  speaking,  pruning  may  be  said  to  influence  fruit-bud  and 
fruit  formation — bearing  habit — in  two  ways,  directly  and  indirectly. 
Its  most  important  direct  influence  is  to  thin  the  crop  through  the  removal 
of  actual  or  potential  fruit-bearing  wood.  Another  rather  direct  influence 
is  its  effect  on  the  location  or  distribution  of  fruiting  wood,  both  spurs 
and  shoots.  Its  indirect  influence  is  effected  mainly  through  changing 
nutritive  conditions  within  the  tree  and  consequently  limiting  or  encour- 
aging fruit-spur  or  fruit-bud  formation.  As  these  indirect  effects  have 
been  considered  rather  fully  in  the  preceding  chapters  but  little  attention 
is  given  them  here.  Furthermore  no  attempt  is  made  to  discuss  the 
influence  of  different  pruning  treatments  on  the  fruiting  habits  of  any  of 
the  tropical  or  subtropical  fruits  or  of  a  number  of  the  less  common  and 
less  important  deciduous  fruits. 

Pruning  the  Apple  and  the  Pear. — As  has  been  pointed  out,  apple  and 
pear  flowers  are  for  the  most  part  borne  terminally  on  short  growths 

457 


458  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

springing  from  terminal  buds  on  other  short  growths,  or  spurs.  Indi- 
vidual spurs  are  wont  to  bear  only  every  other  year,  though  annual 
bearing  spurs  are  not  rare  and  are  common  in  trees  of  certain  varieties. 
More  frequently,  however,  individual  spurs  fail  to  produce  even  every 
other  year,  bearing  perhaps  only  once  in  3  or  4  years,  or  very  irregularly. 
These  spurs  may  live  many  years  and  there  is  nothing  in  their  manner  of 
growth  to  necessitate  a  deterioration  in  efficiency  as  they  grow  older.  In 
reality,  however,  they  flower  and,  more  particularly,  set  and  mature 
fruit,  much  less  regularly  as  they  increase  in  age.^^  Without  doubt  this  is 
due  to  unfavorable  nutritive  conditions  induced  by  crowding  and  compe- 
tition with  other  parts  of  the  tree  for  food,  moisture  and  light.  Records 
show,  nevertheless,  that  even  very  old  spurs  may  bear  good  fruits  and  that 
when  strong  and  vigorous  they  are  more  efficient  fruit  producers  than 
those  that  are  much  younger  but  lacking  in  vigor.  ^^  Roberts^"  has 
reported  a  marked  correlation  between  the  vigor  of  spurs,  as  measured 
by  the  length  of  each  year's  growth  and  by  the  number  and  area  of  their 
leaves  and  performance  in  flower-bud  formation.  Spurs  of  medium 
length  with  relatively  large  leaf  areas  and  consequently  with  the  means 
of  accumulating  reserves  of  elaborated  foods  are  more  likely  to  form 
fruit-buds. 

Heavy  annual  production,  then,  would  seem  among  other  things 
to  depend  on  (1)  the  formation  of  an  adequate  supply  of  fruit  spurs, 
(2)  the  retention  of  those  already  formed  and  (3)  maintaining  all  of 
them  in  a  vigorous  condition  so  that  they  may  flower  and  fruit  regularly. 
These  requirements  plainly  cannot  be  met  or  supplied  by  any  single 
pruning  practice  or  by  any  combination  of  pruning  practices.  They 
depend  on  many  factors,  chief  among  which  are  nutritive  conditions 
within  the  plant,  which,  in  turn,  are  influenced  most  readily  by  ferti- 
Uzers  and  various  systems  of  soil  management.  Pruning,  however, 
is  important  in  this  connection. 

The  Formation  of  Fruit  Spurs. — As  pointed  out  elsewhere,  maximum 
fruit-spur  formation  is  encouraged  by  leaving  the  trees  unpruned  or  by 
pruning  them  very  lightly.  Such  treatment  or  lack  of  treatment  leaves 
the  largest  possible  number  of  buds  from  which  spm-s  may  develop; 
consequently  an  approach  to  this  treatment  is  recommended  to  induce 
bearing  in  a  short  time.  Formerly  the  artificial  bending  of  long  shoots 
was  quite  generally  recommended  to  make  them  more  fruitful  through 
the  formation  of  fruit  spurs.  However,  recent  investigation  indicates 
that  this  practice  is  of  doubtful  value  and  certainly  is  not  to  be  recom- 
mended under  average  field  conditions. ^^  Experimental  work  at  the 
Oregon  Station  has  shown  that  when  certain  shoots  are  selected  for 
removal  in  young  apple  trees,  new  fruit-spur  formation  is  favored  by 
leaving  those  that  are  vigorous  and  comparatively  upright. ^^  As  the 
trees  become  older  and  possess  fruit  spurs  in  numbers  sufficient  to  pro- 


PRUNING  WITH  SPECIAL  REFERENCE  TO  PARTICULAR  FRUITS    459 

vide  full  crops  less  attention  need  be  given  to  obtaining  new  spurs.  Some 
of  the  old  spurs  die  out  or  are  lost  through  accident  and  new  spurs  are 
needed  tore  place  them  and  of  course  the  numbers  increase  as  the  tree 
grows  older.  Usually,  however,  more  spurs  form  than  the  tree  can 
support  to  advantage  and  it  is  only  in  the  tree  between  4  and  6  or  8  years 
of  age  that  there  is  need  of  definite  effort  to  encourage  their  development. 

Very  rarely  do  new  spurs  form  directly  on  the  old  wood  from  either 
latent  or  adventitious  buds.  In  case  the  spurs  in  the  lower-interior  part 
of  the  tree  die  out  or  are  destroyed  the  only  way  to  develop  new  spurs  in 
that  region  is  to  prune  back  the  top  of  the  tree  somewhat  heavily.  This 
will  force  out  watersprouts  from  latent  or  adventitious  buds.  At  the 
same  time  there  should  be  enough  thinning  out  to  permit  free  access 
of  sunlight  and  thus  promote  the  development  of  large  leaves  and  large 
lateral  buds  which  a  year  later  may  develop  into  fruit  spurs.  These 
watersprouts  are  then  treated  in  very  much  the  same  way  as  the  tops  of 
trees  just  coming  into  bearing;  the  same  may  be  recommended  for  the 
strong  vigorous  growth  in  trees  recently  "dehorned"  or  recently 
top  worked. 

Retaining  Spurs  Already  Established. — Since  the  spurs  of  the  apple 
and  pear  bear  fruit  repeatedly  they  should  obviously  be  retained  as 
long  as  they  remain  efficient  producers.  Yet  many  growers  remove 
them  unnecessarily  at  the  time  of  pruning  or  permit  their  useless  destruc- 
tion by  careless  pickers.  In  some  varieties  particularly,  as  for  example 
the  Esopus  (Spitzenburg)  apple,  new  spurs  do  not  readily  develop  to 
replace  the  old,  because  of  the  difficulty  in  obtaining  sucker  growth  in 
the  interior  of  the  tree;  hence  the  loss  of  any  considerable  number  of 
spurs  is  likely  to  render  those  portions  of  the  tree  permanently  barren. 
There  is  often  occasion  for  prmiing  out  some  of  the  fruiting  wood  of  the 
apple  and  pear;  however,  this  should  be  done  with  caution  and  with  a 
clear  understanding  of  the  problems  involved  in  replacing  it.  The 
advisability  of  much  thinning  of  the  crop  by  means  of  pruning  is  ques- 
tionable in  these  fruits.  The  ultimate  result  of  the  loss  of  spurs  from 
the  interior  and  lower  portions  of  the  tree  is  the  forcing  out  and  up  of 
its  bearing  surface.  Eventually  the  active  fruiting  wood  will  be  around 
the  outside  and  in  the  top  of  the  tree  with  the  major  portion  of  the  interior 
unproductive.  When  a  crop  is  so  distributed,  its  weight  places  the 
greatest  possible  strain  upon  the  crotches  and  the  tree  is  subject  to 
greatest  injury  from  storms  and  winds.  Much  of  the  breakage  in  the 
older  orchards  is  associated  with  this  condition,  which  can  be  largely 
avoided  by  thinning  out  which  limits  the  formation  of  new  fruit  spurs  and 
at  the  same  time  keeps  the  older  spurs  productive. 

Keeping  Spurs  Strong  and  Vigorous. — The  superiority  of  vigorous 
fruit  spurs  over  those  that  are  weak  has  been  mentioned  repeatedly. 
They  flower  and  set  fruit  more  frequently  and  are  much  more  likely  to 


460  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

bring  their  fruits  to  maturity.  Indeed,  some  question  may  be  raised 
as  to  whether  the  very  weak  spurs,  those  that  annually  push  out  only 
two  or  three  small  leaves  and  rarely  or  never  form  fruit  buds,  are  of  any 
real  benefit  to  the  tree.  They  draw  on  the  supply  of  moisture  and 
nutrients  obtained  from  the  soil  and  they  can  yield  but  little  elaborated 
food  in  return.  Furthermore,  observation  indicates  that  forcing  such 
spurs  into  vigorous  growth,  once  they  become  weakened,  is  extremely 
difficult.  Heavy  pruning,  alone  or  combined  with  certain  cultural 
treatments,  may  force  them  to  grow  out  into  new  shoots  and  later  these 
shoots  may  give  rise  to  fruit  spurs;  however,  to  reinvigorate  them  and 
make  them  form  fruit  buds  without  an  intervening  shoot  growth  is 
very  difficult  after  they  have  ceased  to  function  satisfactorily  for  several 
years.  Therefore  keeping  fruit  spurs  in  a  vigorous  condition  from  the 
start  is  doubly  desirable. 

The  vigor  and  growth  of  individual  spurs  depends  on  (1)  the  supply 
of  moisture  and  nutrients  from  the  roots  and  (2)  the  supply  of  elaborated 
foods  stored  more  or  less  locally.  This  locally  stored  supply  in  turn 
depends  largely  on  manufacture  at  or  very  near  the  point  in  question. 
Both  of  these  factors  are  influenced  by  many  cultural  practices.  Pruning 
may  be  a  means  of  modifying,  at  least  temporarily,  the  supply  of  moisture 
and  nutrients  available  for  the  spurs  that  are  left,  through  diverting 
to  them  large  amounts  before  intake  is  correspondingly  reduced.  This 
effect  of  pruning  can  be  obtained  more  readily  by  fertilizing,  tillage, 
irrigation,  mulching  or  other  soil  treatments.  It  may  be  pointed  out, 
however,  that  though  the  effects  attending  these  other  cultural  opera- 
tions and  those  attending  pruning  are  quite  similar,  in  the  one  instance 
there  is  a  general  influence  on  the  vegetative  activities  of  the  tree  while 
pruning  has  a  more  specific  influence  on  certain  of  its  parts  or  local 
regions. 

Pruning  is  a  more  important  means  of  influencing  the  accumulation 
of  elaborated  foods,  through  admitting  more  or  less  light  to  the  spurs. 
As  has  been  pointed  out,  the  general  effect  of  heading  back  is  to  thicken 
the  top,  cause  more  shading  and  thus  probably  decreased  carbohydrate 
manufacture  in  the  lower  and  interior  parts  of  the  tree.  On  the  other 
hand  thinning  out  tends  to  have  the  opposite  effect.  Since  the  removal 
of  spurs  by  thinning  (either  the  removal  of  individual  spurs  or  small 
spur-bearing  branches)  has  as  great  a  concentrating  effect  on  nutrients 
as  an  equivalent  heading  back,  it  is  to  be  regarded  as  the  most  important 
pruning  practice  in  this  respect.  Indeed  it  is  about  the  only  pruning 
practice  that  always  tends  to  increase  longevity  and  regularity  of  bearing 
in  fruit  spurs.  Consequently  the  heading  back  that  is  done  in  bearing 
apple  and  pear  trees  should  be  hmited  to  that  required  to  keep  the  tree 
from  becoming  too  tall  and  too  spreading  for  the  mechanical  support 
of   its   crop   and   for   convenience   in   various   orchard   operations.     In 


PRUNING  WITH  SPECIAL  REFERENCE  TO  PARTICULAR  FRUITS    461 

other  words  heading  back  should  be  done  principally  for  the  purpose 
of  training,  thinning  out  serving  principally  to  affect  its  bearing  habits. 

Suminarij  of  Usual  Pruning  Treatment. — Briefly,  the  general  pruning 
treatment  recommended  for  the  apple  and  the  pear,  considering  their 
growing  and  bearing  habits  and  their  I'csponses  to  different  types  of  prun- 
ing, may  be  stated  as  follows:  During  the  first  few  years  in  the  orchard, 
assuming  at  least  a  moderately  strong  growth,  the  tree  should  be  pruned 
rather  severely  (beginning  with  perhaps  a  75  per  cent  pruning)  and  this 
should  consist  in  both  thinning  out  and  heading  back,  with  the  emphasis 
perhaps  on  heading  back.  This  heavy  pruning  is  for  the  purpose  of 
properly  developing  the  framework  of  the  tree.  If  it  has  made  a  weak 
growth,  pruning  should  be  correspondingly  lighter.  As  the  tree  becomes 
older,  pruning  gradually  decreases  in  severity  until  at  6  or  7  years,  when  it 
reaches  bearing  age  and  size,  very  little  is  done.  As  pruning  slowly 
lessens  in  severity  it  gradually  changes  in  kind,  consisting  less  in  heading 
back  and  more  and  more  in  thinning  out.  This  general  procedure  devel- 
ops a  fruit-spur  system  and  brings  it  into  bearing.  After  the  tree  is  once 
in  bearing,  pruning  slowly  increases  in  amount  but  continues  to  be 
mainly  a  thinning  out;  this  thinning  should  comprise  the  removal  of  small 
limbs  throughout  the  top  rather  than  the  cutting  of  a  few  large  limbs. 
When  this  plan  is  followed  there  is  some  thinning  of  fruit  spurs  and  of  the 
fruit  crop,  overbearing  is  prevented  and  the  length  of  life,  regularity  of 
bearing  and  efficiency  of  individual  spurs  are  promoted. 

Special  Suggestions  for  Unusual  Fruiting  Habits. — Certain  varieties 
of  the  apple  and  the  pear  have  been  said  to  bear  many  fruit  buds  termi- 
nall}'  or  laterally  on  long  shoots.  This  is  particularly  common  during 
the  period  when  they  are  just  coming  into  bearing.  Under  these  cir- 
cumstances greater  care  must  be  exercised  against  the  unnecessary  removal 
of  any  new  shoots  and  heading  back  should  be  reduced  to  a  minimum 
until  the  trees  have  a  better  developed  fruit  spur-system  and  are  bearing 
a  considerable  percentage  of  their  crop  on  it.  The  production  of  lateral 
fruit  buds  on  long  shoots,  it  should  be  noted,  presents  a  case  quite  similar 
to  that  of  the  peach  and  consequently  the  pruning  of  such  trees  should 
resemble  that  ordinarily  given  peach  trees  as  much  as  it  does  that  of  the 
average  apple  or  pear  variety.  However,  most  of  these  lateral  fruit  buds 
in  the  apple  are  borne  on  the  terminal  half  or  even  third  of  the  shoot, 
while  a  considerable  percentage  of  those  of  the  peach  are  found  on  the 
basal  half.  This  necessitates  much  more  care  in  heading  back  the  fruit 
bearing  shoots  in  these  particular  varieties  than  is  requisite  in  the  peach. 
Pruning  the  Peach. — The  peach  is  perhaps  the  best  known  repre- 
sentative of  that  group  of  fruits  which  "bear  lateral  fruit  buds  on  long 
growths  or  shoots.  These  buds  contain  flowers  only  and  with  their 
falling,  or  with  the  maturing  of  the  fruits  which  develop  from  them,  that 
portion  of  the  branch  to  which  they  were  attached  becomes  barren. 


462  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Neither  fruits  nor  flowers  are  again  borne  upon  it.  New  growth  develops 
from  the  terminal  bud  or  from  lateral  leaf  buds  at  some  of  the  non-flower- 
ing nodes  or  in  some  instances  from  adventitious  or  latent  buds  lower  in 
the  tree.  It  is  therefore  characteristic  of  the  peach  to  have  its  fruiting 
wood  carried  a  foot  or  two  further  out  and  up  each  year,  leaving  long 
stretches  of  non-fruiting  wood  that  serves  only  as  a  connecting  link 
between  the  fruiting  periphery  of  the  tree  and  its  root  system. 

Seldom  does  the  peach  tree  of  bearing  age  fail  to  differentiate  enough 
fruit  buds  for  a  heavy  crop.  In  fact  it  commonly  produces  many  more 
than  are  desired,  so  that  some  pruning  is  advisable  for  the  purpose  of 
thinning  the  crop.  Furthermore,  since  the  fruit  buds  are  produced  each 
year  on  the  new  wood  of  the  current  season  there  is  no  danger  of  rendering 
the  tree  unproductive  for  a  period  of  several  years,  as  in  the  apple  or  the 
pear,  by  cutting  away  its  fruiting  wood.  Therefore  the  two  main  prob- 
lems in  pruning  this  fruit  are  to  thin  the  crop  and  to  "keep  the  tree  within 
bounds,"  that  is,  to  prevent  its  fruiting  wood  from  developing  so  far  away 
from  the  trunk  that  propping,  picking,  spraying  and  fruit  thinning  involve 
too  much  expense.  Almost  any  kind  of  pruning  serves  the  latter  purpose 
if  it  is  severe  enough;  on  the  other  hand  the  location  of  the  new  fruiting 
wood  and  the  distribution  of  its  fruit  buds  depend  very  considerably  on 
the  type  of  pruning  that  is  employed.  In  fact  it  would  not  be  far  from 
correct  to  say  that  in  the  bearing  peach  tree  the  severity  of  pruning 
should  be  governed  largely  by  the  amount  of  crop  thinning  required  and 
its  kind  should  be  determined  by  the  desired  distribution  of  the  following 
season's  fruiting  branches  and  fruit  buds. 

When  and  How  Severely. — The  bearing  peach  tree  should  be  pruned 
lightly  or  heavily,  depending  on  whether  it  gives  promise  of  bearing  just 
enough  or  too  much,  if  little  or  no  pruning  is  done.  As  a  rule  prospects 
cannot  be  estimated  accurately  until  the  trees  are  in  bloom  or  even  until 
the  fruit  has  set,  on  account  of  danger  from  late  spring  frosts.  Conse- 
quently it  is  wise  to  wait  until  that  time  and  then  to  prune  with  the  aim 
of  providing  as  nearly  as  possible  a  full  crop  but  still  of  reducing  the  labor 
of  fruit  thinning  to  a  minimum.  If  crop  prospects  are  ruined  by  a  late 
frost  the  trees  can  be  dehorned  advantageously,  because  this  heavy 
pruning  will  not  result  in  any  loss  of  fruit  and  since  new  growth  for  the 
following  season's  production  will  be  forced  to  develop  from  the  main 
scaffold  limbs,  the  bearing  surface  will  be  lowered  and  made  more  com- 
pact. If  midwinter  or  late  winter  freezing  destroys  the  fruit  buds  this 
same  type  of  pruning  can  be  done  earlier. 

Pruning  to  Secure  Most  Favorable  Location  of  Fruiting  Surface. — 
The  usual  method  of  pruning  the  bearing  peach  tree  comprises  such  thin- 
ning out  as  seems  necessary,  this  thinning  consisting  generally  in  the 
removal  of  wood  from  the  center  of  the  tree  so  as  to  provide  an  extreme 
open  center.     In  fact  the  average  peach  tree  as  found  in  the  commercial 


PRUNING  WITH  SPECIAL  REFERENCE  TO  PARTICULAR  FRUITS    463 

orchard  illustrates  more  nearly  the  vase  or  goblet  shaped  form  than  almost 
any  other  species.  This  thinning  out  is  then  followed  by  as  severe  head- 
ing back  of  the  shoots  as  is  compatible  with  leaving  enough  good  fruit 
buds — or  flowers  if  the  operation  has  been  delayed  until  the  blooming 
season — to  provide  for  a  full  crop.  If  the  number  and  distribution  of 
buds  is  such  that  the  heading  back  can  be  rather  severe  the  new  shoot 
growth  will  be  forced  to  come  out  rather  low  and  the  tree  will  be  kept 
relatively  compact,  though  the  fruiting  wood  of  the  following  season  will 
be  necessarily  somewhat  farther  out  from  the  trunk  than  that  of  the 
current  season. 

One  result  of  the  heading  back  will  be  a  crowding  of  the  new  shoot 
growth;  this  will  increase  with  the  severity  of  the  heading  back.  The 
result  is  comparatively  long  slender  shoots,  from  whose  nodes  the  leaves 
soon  fall  because  they  are  shaded.  Only  leaf  buds  will  be  formed  in 
their  axils;  these  will  be  small  and  quite  likely  to  remain  latent  the 
following  year.  Fruit  buds  are  formed  chiefly  on  the  median  or  apical 
portions  of  these  crowding  shoots  or  on  their  secondary  lateral  branches. 
This  necessitates  a  less  severe  heading  back  the  following  spring  if  fruit 
buds  sufficient  in  number  for  a  good  crop  are  to  be  left  and  the  bearing 
portion  of  the  tree  is  pushed  farther  away  from  the  trunk.  Some  shoots 
will  probably  develop  in  the  interior  of  the  tree  from  latent  or  adven- 
titious buds  on  the  main  limbs.  These  should  be  saved  for  renewal 
purposes,  though  usually  it  is  only  a  matter  of  time  before  a  general 
"dehorning"  becomes  necessary  in  order  to  lower  the  top  and  make 
the  tree  sufficiently  compact  for  economical  production. 

A  practice  seldom  employed,  but  frequently  desirable,  is  an  early 
summer  thinning  out  of  the  new  shoots.  Ordinarily  this  should  be  done 
in  late  June  or  early  July,  considerably  before  terminal  bud  formation 
is  under  way.  It  reduces  crowding  and  the  remaining  shoots  are  less 
likely  to  become  long  because  their  internodes  remain  shorter.  Their 
leaves  are  better  lighted  and  those  at  the  basal  nodes  persist  through  the 
season  instead  of  falling  prematurely.  Consequently  fruit  buds  form  at 
these  basal  nodes  as  well  as  at  the  median  or  distal.  This  makes  it 
possible  to  head  back  much  more  severely  the  following  spring  and  still 
leave  provision  for  a  full  crop.  The  fruiting  zone  is  not  carried  so 
far  from  the  trunk  each  year  and  dehorning  is  not  so  frequently  necessary. 
Furthermore,  the  fruit  buds  at  the  more  basal  nodes  enter  the  dormant 
period  at  a  relatively  less  advanced  stage  of  development  than  those 
farther  out  on  the  shoots.  This  makes  them  somewhat  more  resistant 
to  winter  cold  and  a  httle  slower  in  opening  the  following  spring.  The 
practice  also  results  in  the  development  of  many  very  short  shoots  that 
amount  almost  to  fruit  spurs  bearing  lateral  fruit  buds — a  fruiting  habit 
closely  resembling  that  of  the  apricot  or  almond.  This  means  in  effect 
a  tree  that  mechanically  is  much  stronger  than  the  average.     The  summer 


464  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

pruning  here  suggested  could  easily  be  overdone.  It  should  not  remove 
so  much  new  growth  that  the  developing  fruit  is  subjected  to  danger 
from  sunscald  or  that  the  formation  of  secondary  shoots  is  stimulated. 
It  should  be  well  distributed  through  the  top  and  outer  portions  of  the 
tree,  as  its  effectiveness  depends  on  making  possible  a  better  distribution 
of  sunlight  to  the  leaves  on  the  lower  portions  of  the  new  shoots.  If 
carefully  done  it  reduces  greatly  the  amount  of  shoot  thinning  that  will 
be  required  the  following  spring  and  the  yearly  pruning  treatment  really 
becomes  a  summer  thinning  out  and  a  winter  heading  back.  Inci- 
dentally it  is  of  considerable  aid  in  promoting  coloration  of  the  fruit. 

Pruning  the  Sweet  Cherry. — Typical  of  that  group  of  fruits  whose 
flower  buds  are  borne  laterally  on  short  spurs  and  give  rise  to  an  inflores- 
cence only  is  the  sweet  cherry.  The  terminal  of  the  sweet  cherry  spur  is 
always  a  leaf  bud  by  which  the  growth  of  the  spur  is  continued  each  year. 
New  spurs  originate  from  some  of  the  lateral  leaf  buds  on  the  shoots  of  the 
preceding  season  and  new  shoot  growth  proceeds  from  other  lateral  buds, 
from  terminal  buds  on  shoots,  from  latent  or  adventitious  buds  on  the 
older  wood  and  occasionally  from  the  terminal  buds  of  spurs.  However, 
comparatively  few  shoots  arise  from  buds  of  the  last  two  classes  in  the 
sweet  cherry.  The  lateral  buds  on  the  year-old  shoots  of  young  vigor- 
ously growing  trees  are  little  inclined  to  produce  spurs,  but  either  grow 
out  into  new  shoots  or  remain  dormant.  Consequently  the  young  trees 
of  this  species  are  thick  brushy  growers,  strongly  vegetative  in  character 
and  often  slow  in  coming  into  bearing.  Old  trees  of  the  same  species 
present  a  rather  sharp  contrast  to  this  condition.  Most  of  the  lateral 
buds  on  their  shoots  produce  spurs  or  remain  dormant.  Often  new  shoot 
growth  is  produced  mainly  from  the  terminal  buds  of  the  last  year's 
shoots,  the  result  being  a  tree  that  is  markedly  reproductive  and  often 
lacking  in  vigor. 

As  the  problem  in  the  young  tree  is  first  to  secure  a  strong  framework 
and  then  a  good  equipment  of  fruit  spurs,  much  as  in  the  apple  and 
pear  and  as  its  shoots  and  spurs  originate  from  buds  in  the  same  locations, 
its  pruning  treatment  the  first  few  years  should  correspond  closely  to 
that  of  those  fruits.  In  other  words  pruning  should  be  fairly  heavy  at 
first,  gradually  decreasing  in  amount  till  at  6  or  7  years  little  is 
done.  At  the  same  time  it  should  change  gradually  from  a  treatment 
which  consists  largely  in  heading  back  to  one  which  consists  almost 
entirely  in  thinning  out. 

As  the  tree  becomes  older,  however,  its  pruning  treatment  should  div- 
erge gradually  from  that  customarily  given  the  apple  or  pear.  Its  natural 
tendency  to  produce  large  numbers  of  fruit  spurs  obviates  the  necessity 
of  employing  any  treatment  to  encourage  greater  spur  and  fruit  bud 
production.  At  the  same  time  this  growing  habit  results  in  a  fairly 
open  top  in  which  the  foliage  is  well  exposed  to  light.     On  the  other 


PRUNING  WITH  SPECIAL  REFERENCE  TO  PARTICULAR  FRUITS    465 

hand  measures  should  be  taken  to  promote  a  greater  vegetative  growth, 
particularly  in  those  varieties  or  under  those  conditions  that  tend  toward 
the  development  of  new  shoots  from  terminal  buds  only.  Otherwise 
long  pole-like  fruiting  branches,  subject  to  much  injury  from  the  wind 
when  heavily  loaded  with  fruit,  will  develop.  Heading  back  to  promote 
branching,  however,  must  be  done  with  considerable  care.  If  the 
heading  is  into  2-year,  3-year,  or  older  wood  new  side  branches  are  not 
likely  to  form  and  the  limbs  in  question  are  subordinated  to  an  unim- 
portant position  in  the  tree.  Heading  back  to  near  the  base  of  the  one- 
3^ear  old  shoots  is  much  more  likely  to  induce  the  branching  desired, 
though  this  alone  is  often  rather  ineffective  in  large  trees  somewhat 
lacking  in  vigor.  A  certain  amount  of  pruning  back  to  2-year,  3-year 
or  older  laterals  is  often  effective  in  keeping  the  tree  within  bounds. 
There  is  little  occasion  to  do  much  thinning  out  in  the  sweet  cherry  tree 
that  is  well  in  bearing  and  the  heading  back  is  mainly  for  the  purpose  of 
lowering  the  top  and  correcting  form.  Dehorning  is  seldom  resorted  to 
because  of  the  poor  response  in  new  shoot  growth  that  often  follows  this 
operation  and  because  of  the  time  required  for  the  formation  of  a  good 
supply  of  new  spurs  before  the  tree  can  again  come  into  heavy  bearing. 

Generally  speaking,  then,  the  pruning  of  the  bearing  sweet  cherry 
should  be  light  in  amount  and  for  correcting  and  improving  shape.  On 
account  of  the  growing  habit  this  means  that  it  will  consist  largely  in 
heading  back.  Other  orchard  practices,  such  as  cultivation,  irrigation 
and  fertilization,  should  be  counted  on  to  encourage  a  strong  new  shoot 
growth  which  can  be  headed  back  to  promote  branching  and  compactness 
of  tree. 

Pruning  the  Almond,  Apricot,  Plum,  and  Sour  Cherry. — As  has  been 
stated  in  the  classification  of  fruiting  habits,  the  almond,  apricot,  plum 
and  sour  cherry  form  a  series  intermediate  in  their  habits  of  bearing 
between  the  peach  on  the  one  hand  and  the  sweet  cherry  on  the  other. 
That  is,  all  of  these  fruits  bear  fruit-buds  laterallj^  on  both  long  and  short 
growths.  Some  of  them,  as  certain  of  the  almonds  and  Japanese  plums, 
approach  the  peach  more  closely;  others,  as  the  Insititia  plums,  approach 
the  sweet  cherry  more  closely.  The  age  and  vigor  of  the  trees  and  the 
cultural  conditions  under  which  they  are  grown  influence  the  relative 
distribution  of  fruit  buds  on  spurs  and  on  shoots.  Roberts*^  states  that 
weak  or  moderately  vigorous  sour  cherry  trees  bear  a  much  larger  per- 
centage of  their  fruit  buds  on  medium  to  short  shoots  than  do  the  vigorous 
trees  of  the  same  varieties.  The  reverse  is  likely  to  hold  in  certain  varie- 
ties of  the  Japanese  plum. 

Since  the  bearing  habits  of  these  fruits  are  intermediate  between 
those  of  the  peach  and  of  the  sweet  cherry,  it  follows  that  their  pruning 
treatments  should  likewise  be  intermediate  between  those  given  typical 
bearing  trees  of  those  species.     If  the  bearing  habit  is  more  like  that 


466  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

of  the  peach  the  pruning  treatment  should  be  correspondingly  severe; 
if  it  is  more  like  that  of  the  sweet  cherry  it  should  be  correspondingly  light. 
In  kind,  likewise,  it  should  resemble  that  of  the  fruit  whose  bearing  habit 
it  most  closely  resembles.  Furthermore,  with  a  change  in  the  bearing 
habit  as  the  tree  grows  older  or  as  its  environment  varies  there  should  be  a 
corresponding  change  in  the  amount  and  kind  of  pruning. 

In  general  with  these  fruits  it  is  usually  desirable  to  employ  those 
cultural  and  pruning  practices  that  encourage  the  spur-bearing,  rather 
than  the  shoot-bearing,  habit.  The  production  of  fruits  on  spurs  means 
compactness  of  trees,  less  danger  from  the  breaking  of  limbs  and  lighter 
and  less  expensive  pruning.  There  is  not  the  necessity  of  constant  prun- 
ing for  "renewal"  purposes.  It  has  been  found  in  the  sour  cherry  at 
least  that  spur-borne  fruit  buds  are  hardier  than  those  borne  on  shoots.  ^^ 
Pruning  the  Currant  and  Gooseberry. — The  fruiting  habits  of  the 
currant  and  the  gooseberry  resemble  that  of  the  apricot  more  closely  than 
those. of  any  of  the  other  tree  fruits.  Within  certain  limits  their  pruning 
treatment  should  follow  closely  that  found  best  suited  to  the  apricot. 
Since  the  currant  and  gooseberry  are  bush,  rather  than  tree,  fruits,  they 
have  a  marked  tendency  to  throw  out  strong  vigorous  new  shoots  from 
the  crown  or  from  the  base  of  the  old  canes.  The  growth  of  this  wood, 
together  with  fruiting  of  the  older  wood,  weakens  the  latter  and  a  point 
is  soon  reached  where  its  retention  is  no  longer  profitable.  Experience 
has  demonstrated  that  canes  more  than  four  years  old  should  be  removed 
to  make  room  for  the  younger  and  more  vigorous  growth.  As  a  rule  more 
new  shoots  form  each  season  than  can  be  retained  without  undue  crowd- 
ing. Consequently  they  are  thinned  each  spring  to  from  3  to  6  of  the 
strongest  and  best  distributed;  these  are  headed  back  to  a  height  of 
2  or  3  feet  to  keep  the  bush  more  compact.  Thus,  when  the  currant 
or  gooseberry  plantation  once  becomes  well  established,  its  annual 
pruning  actually  comprises  a  removal  of  the  old  canes  that  are  becoming 
weak  and  a  thinning  of  the  new  shoots  to  make  provision  for  the  replacing 
of  the  old  wood  that  is  discarded.  Injured  or  diseased  canes  are  of 
course  removed  and  some  attention  should  be  devoted  to  training. 

Certain  varieties  or  types  that  have  growing  or  fruiting  habits 
different  from  those  described  as  typical  should  receive  a  correspondingly 
different  pruning  treatment.  The  wood  of  the  black  currant  loses  its 
vigor  and  becomes  relatively  unproductive  at  an  earlier  age  than  that  of 
the  red  currant  or  the  gooseberry.  Consequently  the  old  canes  are 
removed  after  they  have  fruited  1  or  2  years  and  a  correspondingly  larger 
number  of  new  shoots  are  retained  each  season  for  replacement  purposes. 

Both  currants  and  gooseberries  may  be  trained  in  either  the  bush  or 
the  tree  form.  In  America  the  bush  form  is  preferable,  both  because 
less  labor  is  required  in  training  and  because  it  lends  itself  more  readily 
to  an  economical  control  of  the  currant  borer. 


PRUNING  WITH  SPECIAL  REFERENCE  TO  PARTICULAR  FRUITS    467 

Pruning  the  Brambles. — Most  of  the  bramble  fruits  are  perennials, 
with  biennial  canes.  The  dying  of  the  canes  at  the  end  of  their  fruiting 
season  the  second  year  necessitates  their  removal.  Experience  demon- 
strates that  it  is  good  practice  to  cut  out  and  destroy  the  old  canes 
promptly  after  the  fruiting  season.  Their  retention  until  the  following 
fall  or  spring  can  serve  no  useful  purpose  and  they  prove  a  source  for  the 
spread  of  diseases  and  insects  to  the  new  growth  if  they  are  allowed  to 
remain. 

The  early  spring  pruning  of  this  group  usually  consists  in  some  thin- 
ning out  of  the  cane  growth  that  is  to  bear  fruit  during  the  following 
summer  and  at  the  same  time  a  heading  back  of  the  main  canes  or  of  their 
laterals,  or  perhaps  of  both.  This  pruning  is  done  almost  exclusively  for 
the  purpose  of  thinning  the  crop.  If  done  properly  it  reduces  the  number 
of  fruit  buds  but  results  in  little  or  no  reduction  in  the  total  yield.  Natur- 
ally its  severity  varies  greatly  with  variety  and  with  the  environmental 
conditions.  The  moisture  supply  during  the  ripening  season  limits  yield 
in  the  bramble  fruits  probably  more  frequently  than  any  other  single 
factor.  Consequently  the  severity  of  the  pruning  should  be  influenced  by 
the  prospect  for  available  water  during  and  just  before  harvesting. 
Under  conditions  of  ample  rainfall  or  abundant  irrigation  water  and  of 
relatively  high  atmospheric  humidity  this  pruning  may  be  much  less 
severe  than  when  summer  drought  is  likely.  The  bulk  of  this  spring 
pruning  of  dormant  or  nearly  dormant  canes  should  consist  in  heading 
back  rather  than  in  thinning  out.  The  laterals  from  the  median  and 
more  basal  fruit  buds  generally  produce  larger  clusters  and  their  indi- 
vidual berries  are  larger  than  those  from  the  more  apical  buds.  It  is  a 
good  plan  to  delay  this  pruning  until  the  buds  are  swelling  in  the  spring  so 
that  the  winter-injured  ends  of  the  canes  may  be  removed  without  extra 
labor. 

The  summer  pinching  of  the  bramble  fruits  has  been  discussed  under 
the  heading  of  Pinching  and  need  not  be  treated  at  this  point. 

Few  or  no  data  are  available  showing  the  best  methods  of  pruning 
certain  types  of  the  blackberry  that  have  perennial  canes.  However, 
observation  indicates  that  they  can  be  handled  best  by  treating  them  as 
ordinary  varieties  with  biennial  canes.  That  is,  their  canes  are  pruned 
out  as  soon  as  they  have  fruited  once,  even  though  they  would  bear  a 
second  crop  were  they  allowed  to  remain. 

The  so-called  everbearing  or  fall-bearing  raspberries  produce  their 
late  summer  crop  terminally  on  the  main  shoot  or  on  sub-terminal  laterals 
of  shoots  of  the  current  season.  The  following  main-season  crop  is 
borne  on  laterals  coming  from  lower  parts  of  the  same  canes.  They 
should  be  winter  pruned  in  the  same  way  as  related  mid-season  varieties. 

Pruning  the  Grape. — More  has  been  written  about  pruning  and 
training  the  grape  than  any  other  fruit.     Many  different  systems  or 


4.68  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

methods  have  been  worked  out  and  described  in  detail  and  an  examina- 
tion of  any  considerable  part  of  this  literature  is  as  likely  to  be  confusing 
as  it  is  enlightening.  This  is  not  because  the  several  practices  differ  so 
much  in  the  principles  involved,  but  because  there  is  so  great  diversity  in 
the  methods  of  their  application  that  the  principles  themselves  are 
likely  to  remain  hidden. 

As  pointed  out  in  the  classification  of  bearing  habits,  the  grape  pro- 
duces its  fruit  buds  laterally  on  shoots,  which  at  the  close  of  the  growing 
season  and  for  a  year  thereafter  are  called  canes.  These  fruit  buds  give 
rise  to  flower-bearing  or  fruiting  shoots  on  which  the  inflorescences  appear 
to  be  lateral.  However,  many  shoots  form  few  or  no  fruit  buds,  particu- 
larly those  springing  from  latent  or  adventitious  buds  on  2-year-old 
or  older  wood — in  Other  words,  those  arising  from  the  arms,  head,  trunk 
or  crown  of  the  plant.  Only  those  shoots  (canes,  when  a  year  old)  coming 
from  lateral  buds  on  the  canes  of  the  preceding  season  are  sure  to  form 
fruit  buds,  though  under  some  conditions  those  coming  from  the  older 
wood  differentiate  a  limited  number.  Furthermore  not  all  buds  on  shoots 
springing  from  the  preceding  year's  canes  contain  flower  parts.  Those 
at  the  basal  one  to  four  or  five  nodes,  depending  largely  on  variety,  seldom 
do.  Though  it  is  difficult,  and  often  impossible,  to  distinguish  the  fruit 
buds  from  the  leaf  or  wood  buds  by  their  external  appearance,  their 
position  on  the  plant  offers  a  rather  accurate  index  to  their  character 
and  the  grower  or  student,  once  he  becomes  well  acquainted  with  the 
characteristics  of  the  individual  variety,  will  have  little  difficulty  in  telling 
which  are  of  the  one  kind  and  which  of  the  other. 

Severity  of  Pruning. — Practically  all  grape  vines  differentiate  each 
year  more  fruit  buds  than  can  grow  into  fruiting  shoots  and  set  and  mature 
grapes  the  following  season.  It  is  therefore  unnecessary  in  pruning  the 
grape  to  give  thought  to  securing  larger  numbers  of  fruit  buds.  The  real 
problem  is  that  of  reducing  to  just  the  right  number  those  that  are  already 
formed  and  normally  would  or  could  produce  fruiting  shoots  the  following 
season.  Furthermore,  this  must  be  done  in  such  a  way  that  the  fruit 
will  be  well  distributed  and  that  the  new  shoots  on  which  fruit  buds  for  a 
succeeding  crop  are  differentiated  will  be  so  located  as  to  preserve  the 
compactness  and  established  form  of  the  vine. 

The  reduction  of  fruit  buds  to  just  the  right  number  is  often  difficult 
and  always  requires  an  accurate  knowledge  of  fruit-bud  location  in  the 
particular  variety  and  good  judgment  as  to  how  much  fruit  the  vine 
should  bear.  Overpruning  reduces  the  crop  and  diverts  the  energies  of 
the  plant  into  excessive  wood  growth.  This  is  well  illustrated  by  the 
work  of  Maney^"*  in  Iowa.  Underpruning  permits  the  plant  to  overbear, 
resulting  in  too  many  clusters,  undersized  berries  of  inferior  quality  and  a 
weakening  of  the  vine  itself  so  that  succeeding  crops  will  be  reduced  in 
size  and  the  life  of  the  plant  shortened.     These  statements,  of  course, 


PRUNINd  WITH  SPECIAL  REFERENCE  TO  PARTICULAR  FRUITS  469 

apply  to  the  priming  of  many  other  fruit  phmts,  but  not  to  the  same 
extent  that  they  do  to  the  grape.  In  practice  perhaps  the  best  way  of 
determining  the  severity  of  pruning  is,  following  a  suggestion  of  Hed- 
rick,2^  to  figure  the  problem  for  each  vine  on  a  mathematical  basis.  He 
says  in  reference  to  varieties  of  the  Labrusca  and  Labrusca-hybrid  types: 
"A  thrifty  grape-vine  should  yield,  let  us  say,  15  pounds  of  grapes,  a 
fair  average  for  the  mainstay  varieties.  Each  bunch  will  weigh  from 
a  quarter  to  a  half  pound.  To  produce  15  pounds  on  a  vine,  therefore, 
will  require  from  30  to  GO  ])unches.  As  each  shoot  will  bear  two  or  three 
bunches,  from  15  to  30  buds  must  be  left  on  the  canes  of  the  preceding 
year.  .  .  .  Pruning,  then,  consists  in  calculating  the  number  of  bunches 
and  buds  necessary  and  removing  the  remainder."  As  some  of  the  fruit- 
ing shoots  may  be  broken  off  incident  to  the  work  of  cultivation,  spraying 
or  other  vineyard  operations,  it  may  be  well  to  leave  a  few  extra  fruit 
buds;  this  matter,  however,  can  be  overdone  easily. 

Special  mention  should  be  made  of  the  variation  in  the  relative 
amounts  of  pruning  to  be  given  vines  of  any  given  variety,  not  only  with 
their  age  and  the  conditions  of  soil  moisture  and  fertility  but,  in  grafted 
vines,  with  the  stocks  on  which  they  are  grown.  Certain  stocks  have  the 
reputation  of  producing  shy-bearing  vines,  though  actually  they  are 
unproductive  only  when  pruned  too  closely. 

Another  point  already  mentioned  is  the  provision  that  should  be  made 
for  the  production  of  properly  placed  new  shoots  on  which  fruit  buds  for 
the  following  crop  can  form.  In  practice  this  "proper  distribution" 
generally  involves  their  location  as  near  the  head  of  the  vine  as  possible, 
so  that  the  fruiting  wood  is  not  pushed  out  unnecessarily  each  season; 
thus  the  plant  is  kept  compact.  In  many  varieties  this  is  secured  by 
retaining  the  lowest  or  basal  cane  (fruiting  shoot  of  the  preceding  season) 
on  each  arm  or  spur  and  pruning  away  those  originating  farther  from  the 
head.  In  certain  other  varieties,  however,  the  fruiting  shoots  develop 
only  from  buds  at  nodes  some  distance  from  the  base  of  the  canes  and  the 
more  basal  buds  remain  dormant  when  the  heading  back  is  light  enough 
to  permit  the  development  of  fruiting  shoots.  Pruning  varieties  with 
such  growing  and  fruiting  habits  in  the  way  just  described  would  quickly 
carry  the  bearing  surface  of  the  vine  far  from  its  head  and  necessitate 
frequent  resort  to  pi-uning  like  that  called  dehorning  in  tree  fruits.  The 
usual  method  of  handling  vines  of  this  type  is  each  year  to  prune  lightly 
or  moderately  certain  canes  for  fruit  production,  leaving  them  with  the 
requisite  number  of  fruit  buds  and  to  prune  severely  other  canes  so  that 
all  their  fruit  buds  are  removed  and  they  are  forced  to  develop  vegetative 
shoots  from  their  basal  buds.  These  vegetative  shoots  then  become  the 
fruiting  canes  of  the  following  year,  while  those  that  have  borne  fruit 
are  entirely  removed.  These  much  shortened  canes  are  spoken  of  as 
"renewal  spurs." 


470  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Kind  of  Pruning. — Pruning  the  grape,  like  the  pruning  of  most  other 
fruits,  includes  some  thinning  out  and  some  heading  back.  The  relative 
amounts  of  these  two  types  desirable  in  any  given  case  depend  largely  on 
the  style  of  training  employed.  Invariably  all  the  past  season's  shoots 
are  removed  except  those  retained  for  their  fruit  buds  or  for  "renewal" 
or  "replacement."  This  is  a  thinning  out  process.  If  the  style  of  train- 
ing calls  for  pruning  to  spurs,  more  of  last  season's  shoots  must  be 
retained ;  consequently  there  can  be  less  thinning  out  than  if  the  vines  are 
pruned  to  canes.  As  the  pruning  should  leave  a  fairly  definite  number  of 
fruit  buds,  the  amount  of  heading  back  of  the  canes  left  after  thinning 
varies  inversely  with  their  number.  Thus  there  is  much  less  severe 
heading  with  a  two-wire  Kniffin  system  of  training  than  with  pruning 
back  to  spurs.  Little  need  be  said  at  this  point  regarding  the  summer 
pruning  of  the  grape,  as  the  more  important  features  are  discussed  in 
Chap.  XXIV. 

Methods  of  Training. — As  already  indicated,  there  is  almost  endless 
variety  in  methods  of  training  the  vine.  A  description  of  each,  even  of 
those  that  are  fairly  distinct,  would  require  many  pages  and  probably 
would  be  of  little  real  use.  The  fundamental  objects  of  all  these  methods 
differ  little  from  those  governing  the  training  of  other  fruit-producing 
species.  Training  should  increase  yields,  improve  grades  or  quality  and 
reduce  production  costs  through  facilitating  other  vineyard  operations. 
In  this  fruit  the  usual  training  methods,  at  least  those  employed  in 
America,  have  little  influence  on  total  yields. ^^  They  do,  however,  affect 
quality  and  production  costs.  No  one  method  of  training  is  necessary 
for  the  production  of  fruit  of  the  highest  grade  or  quality.  Thus  in  New 
York,  vines  of  the  Concord  have  been  found  to  mature  their  fruit  better 
when  trained  to  the  umbrella  Kniffin  system  than  when  trained  in  any  of 
the  other  ways  standard  in  that  state. ^^  Husmann  and  Bearing^"  report 
that  in  Muscadine  grapes  the  upright  system  permits  the  fruit  to  ripen 
more  evenly  than  does  the  overhead  system.  Only  after  a  careful  study 
of  the  growing  and  fruiting  characteristics  of  the  different  varieties  in 
various  sections  and  soils  and  on  different  stocks  can  the  best  system 
of  training  be  selected  and  the  best  system  for  one  variety  may  not  be  best 
for  another  in  the  same  vineyard. 

In  general  those  systems  of  training  in  which  the  new  shoots  are 
allowed  to  droop  are  much  less  costly  than  those  in  which  they  are  tied 
in  horizontal  or  vertical  positions;  consequently  it  is  only  under  special 
conditions  that  these  latter  methods  of  training  are  to  be  recommended. 
Along  the  northern  limits  of  outdoor  grape  culture  some  of  the  low  renewal 
systems  of  training  greatly  facilitate  the  work  incident  to  artificial 
winter  protection  and  are  quite  generally  employed.  Those  varieties 
whose  canes  bear  fruit  buds  almost  to  the  very  base,  are  naturally  better 
suited  to  Spur  renewal  than  those  whose  canes  habitually  form  only 


PRUNING  471 

wood  buds  in  the  same  regions.  With  these  latter  cane  renewal  or  a 
combination  of  long  and  short  spur  renewal  is  more  practicable.  Only 
those  varieties  (particularly  of  the  Vinifera  group)  with  comparatively 
stocky  and  rigid  trunks  that  require  no  artificial  supports  can  be  trained 
to  the  tree  form  advantageously.     Other  varieties  require  trellising. 

Suggested  Collateral  Readings 

Howe,  G.  H.     The  Effect  of  Various  Dressings  on  Pruning  Wounds  of  Fruit  Trees. 

N.  Y.  Agr.  Exp.  Sta.  Bui.  396.     1915. 
Roberts,  R.  H.     Prune  the  Cherry  Trees.     Wis.  Agr.  Exp.  Sta.  Bui.  298.     1919. 
Tufts,  W.  P.     Pruning  Young  Deciduous  Fruit  Trees.     Cal.  Agr.  Exp.  Sta.  Bui.  313. 

1919. 
Alderman,  W.  H.,  and  Auchter,  C.  E.     The  Apple  as  Affected  by  Varying  Degrees  of 

Dormant  and  Seasonal  Pruning.     W.  Va.  Agr.  Exp.  Sta.  Bui.  158.     1916. 
Gardner,  V.  R.,  Magness,  J.  R.,  and  Yeager,  A.  F.     Pruning  Investigations.     Ore. 

Agr.  Exp.  Sta.  Bui.  139.     1916. 
Magness,   J.   R.,   Edminster,   A.   F.,   and   Gardner,   V.   R.     Pruning   Investigations. 

Ore.  Agr.  Exp.  Sta.  Bui.  146.     1917. 
Bioletti,  F.  T.     Vine  Pruning  in  California.     Cal.  Agr.  Exp.  Sta.  Bui.  241.     Part  1. 

(No  date.) 
Drinkard,  A.  W.     Fruit  Bud  Formation  and  Development.     Ann.  Rept.  Va.  Agr. 

Exp.  Sta.     Pp.  159-205.     1909-10. 
Sorauer,  P.     A  Popular  Treatise  on  the  Physiology  of  Plants.     Transl.  by  F.  E. 

Weiss.     Pp.  134-168.     London,  1895. 
Bioletti,  F.  T.     Vine  Pruning  in  California.     Cal.  Agr.  Exp.  Sta.  Bui.  246.     Part  2. 

1914. 


Literature  Cited 

1.  Alderman,  W.  H.,  and  Auchter,  E.  C.     \Y.  Va.  Agr.  Exp.  Sta.  Bui.  158.     1916. 

2.  Barry,  P.     The  Fruit  Garden.     Pp.  94-95.     Detroit,  1853. 

3.  Batchelor,  L.  D.,  and  Goodspeed,  W.  E.     Utah  Agr.  Exp.  Sta.  Bui.  140.     1915. 

4.  Bedford,  H.  A.  R.,  and  Pickering,  S.  U.     Science  and  Fruit  Growing.     Pp.  57-80. 

London,  1919. 

5.  Ibid.     P.  46. 

6.  Bioletti,  F.  T.     Cal.  Agr.  Exp.  Sta.  Bui.  241.     1913. 

7.  Blake,  M.  A.,  and  Connors,  C.  H.     N.  J.  Agr.  Exp.  Sta.  Bui.  326.     1917. 

8.  Brierley,  W.  G.     Proc.  Am.  Soc.  Hort.  Sci.     16:  102-104.     1919. 

9.  Card,  F.  W.     Bush  Fruits.     Pp.  48-51;  70-73.     New  York,  1917. 

10.  Chandler,  W.  H.     Mo.  Agr.  Exp.  Sta.  Res.  Bui.  14.     1914. 

11.  Chandler,  W.  H.     Proc.  Am.  Soc.  Hort.  Sci.     16:  88-101.     1919. 

12.  Childs,  L.     Ore.  Agr.  Exp.  Sta.  Bui.  171.     1920. 

13.  Cole,  S.  W.     The  American  Fruit  Book.     P.  57.     Boston,  1850. 

14.  Curtis,  O.  F.     Am.  J.  Bot.     7:  101-124.     1920. 

15.  Daniel,  L.     Compt.  rend.     131:1253-1255.     1900. 

16.  Daniel,  L.     Trav.  scient.  Univ.  de  Rennes.     6  (2) :  22-72.     1907. 

17.  Do\Aaiing,  A.  J.     The  Fruits  and  Fruit  Trees  of  America.     P.  31.     New  York, 

1856. 

18.  Drinkard,  A.  W.     Va.  Agr.  Exp.  Sta.  Ann.  Rept.     Pp.  96-120.     1913-1194. 

19.  Drinkard,  A.  W.     Va.  Agr.  Exp.  Sta.  Tech.  Bui.  17.     1917. 


472  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

20.  Edminster,  A.  F.     Ore.  Agr.  Exp.  Sta.  Bui.  146.     1917. 

21.  Gardner,  V.  R.,  et  al.     Ore.  Agr.  Exp.  Sta.  Bui.  139.     1916. 

22.  Gardner,  V.  R.     Ore.  Agr.  Exp.  Sta.  Bui.  146.     1917. 

23.  Gaucher,  N.     Handb.  der  Obstkultur.     Pp.  602-644.     Berlin,  1902. 

24.  Gladwin,  F.  E.     N.  Y.  Agr.  Exp.  Sta.  Bui.  464.     1919. 

25.  Goumy,  E.     Thesis  Presented  to  the  Faculty  of  Science  of  the  University  of  Paris. 

1905. 

26.  Hedrick,   U.   P.     Manual  of  American   Grape  Growing.     P.    114.     New   York, 

1919. 

27.  Hovey,  C.  M.     Hovey's  Mag.  of  Hort.     15:  301.     1849. 

28.  Howe,  G.  H.     N.  Y.  Agr.  Exp.  Sta.  Bui.  391.     1914. 

29.  Husmann,  G.  C.     U.  S.  D.  A.  Bui.  856.     1920. 

30.  Husmann,  G.  C.,  and  Bearing,  C.     U.  S.  D.  A.,  Bur.  Pi.  Ind.  Bui.  273.     1913. 

31.  Macoun,  W.  T.     Can.  Dept.  Agr.  Bui.  56.     1907. 

32.  Magness,  J.  R.     Ore.  Agr.  Exp.  Sta.  Bid.  139.     1916. 

33.  Magness,  J.  R.  et  al.     Ore.  Agr.  Exp.  Sta.  Bui.  146.     1917. 

34.  Maney,  T.  J.     la.  Agr.  Exp.  Sta.  Bui.  160.     1915. 

35.  Paddock,  W.     N.  Y.  Agr.  Exp.  Sta.  Bui.  151.     1898. 

36.  Paddock,  W.,  and  Whipple,  O.  B.     Fruit  Growing  in  Arid  Regions.     P.   112. 

New  York,  1910. 

37.  Pearson,  A.  H.     J.  Roy.  Hort.  Soc.     29:  274.     1896. 

38.  Quinn,  P.  T.     Pear  Culture  for  Profit.     P.  72.     New  York,  1889. 

39.  Quintinye,  J.  de  la.     Instructions  pour  les  jardins  fruitiers  et  potagers.     2:  579. 

Paris,  1746. 

40.  Ravaz,  L.     Taille  hative  ou  taille  tardive.     1912.     (Cited  by  Bioletti,  F.  T., 

Cal.  Agr.  Exp.  Sta.  Bui.  241.     1913.) 

41.  Rivers,  T.     The  Miniature  Fruit  Garden.     P.  8.     New  York,  1866. 

42.  Ibid.     Pp.  12,  82. 

43.  Roberts,  R.  H.     Wis.  Agr.  Exp.  Sta.  Bui.  298.     1919. 

44.  Roberts,  R.  H.     Wis.  Agr.  Exp.  Sta.  Bui.  317.     1920. 

45.  Taft,  L.  R.,  and  Lyon,  T.  T.     Mich.  Agr.  Exp.  Sta.  Bui.  169.     1899. 

46.  Thomas,  J.  J.     American  Fruit  Culturist.     P.  82.     New  York,  1867. 

47.  Tufts,  W.  P.     Cal.  Agr.  Exp.  Sta.  Bui.  313.     1919. 

48.  Vidal,  J.  L.     Rev.  de  Viticulture.      1:895-903.     1894. 

49.  Vincent,  C.  C.     Ida.  Agr.  Exp.  Sta.  Bui.  98.     1917. 

50.  Volck,  W.  H.     Mo.  Bui.  Cal.  St.  Com.  Hort.     6:  80-89.     1917. 

51.  Waugh,  F.  A.     The  American  Apple  Orchard.     P.  90.     New  York,  1912. 

52.  Yeager,  A.  F.     Ore.  Agr.  Exp.  Sta.  Bui.  139.     1916. 


SECTION  V 
FRUIT  SETTING 

It  is  customary  to  speak  of  the  reproductive  activities  of  the  plant 
as  distinct  from  its  vegetative  activities.  That  use  of  terms  is  accepted 
and  followed  here,  though  it  is  not  always  an  easy  matter  to  define  the 
two.  The  woody  tissues  of  the  shoot  and  spur  may  by  common  consent 
be  considered  vegetative  in  character.  Likewise,  it  is  generally  agreed 
that  the  ovarian  tissues  of  the  fruit  may  be  classed  as  reproductive, 
being  more  intimately  associated  with  reproduction  than  with  vegetative 
growth.  On  the  other  hand,  there  might  easily  be  some  difference  in 
opinion  regarding  the  tissues  composing  the  peduncle  or  central  axis  of  the 
inflorescence.  In  many  plants  these  structures  differ  but  little  from 
other  stem  structures  and  they  are  vegetative  in  character.  On  the 
other  hand,  when  these  tissues  become  fleshy  and  form  an  integral  part 
of  the  developing  fruit,  as  they  do  in  the  pineapple,  fig  and  many  other 
fruits,  they  would  as  naturally  be  considered  along  with  the  ovarian 
tissues  with  which  they  are  so  closely  associated.  Mention  is  made  of 
these  points  to  emphasize  the  fact  that  the  problem  of  fruit  setting  is  not 
necessarily  limited  to  a  consideration  of  strictly  reproductive  tissues 
and  reproductive  activities.  Indeed,  the  formation  of  an  abscission  layer 
at  the  base  of  the  ovary,  the  pedicel  or  the  peduncle  is  a  function  of  the 
sporophytic  tissue  at  that  point.  Consequently  it  is  subject  to  the  same 
influences,  though  perhaps  not  to  the  same  extent  or  in  exactly  the  same 
way,  as  abscission  layers  developed  in  other  places.  However,  fruit 
setting  and  fruit  formation  depend  on  the  initiation  and  successful 
completion  of  at  least  some  of  the  reproductory  processes.  Therefore, 
the  more  important  of  the  processes  more  or  less  directly  concerned  with 
the  setting  of  fruit  are  outlined  briefly. 

In  the  great  majority  of  higher  plants,  fruit  and  seed  formation  are 
conditioned  on  the  bringing  together  and  fusion  of  two  specialized  cells 
known  as  gametes.  The  larger  of  these  cells  is  called  the  egg  and  is 
borne  in  the  embryo  sac.  The  smaller  gametes  are  formed  by  a  divi- 
sion of  the  generative  nucleus  of  the  pollen  grain.  The  flower  is  the 
special  organ  of  the  plant  for  the  production  of  these  gametes.  More 
specifically  the  stamen  or  microsporangium  is  the  organ  for  the  pro- 
duction of  the  male  gametes  and  the  ovule  or  macrosporangium  the 
organ  for  the  production  of  the  female  gametes.     The  great  diversity 

473 


474 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


in  the  size,  form,  color  and  odor  of  flowers  docs  not  modify  the  funda- 
mental processes  which  take  place,  following  pollination,  in  the  growth  of 
the  pollen  tube  or  in  fertilization.  In  this  discussion,  therefore,  but 
little  attention  need  be  given  to  the  structure  of  the  so-called  non- 
essential flower  organs. 


r^^ 


Plate  I.— Successive  stages  in  the  development  of  the  ovule  of  the  orange.  In  Figure 
1,  mm  =  macrospore,  u  =  inner  integument,  and  oi  =  outer  integument.  Figs.  2  and  3, 
later  stages  in  which  the  integument  more  nearly  encloses  the  nucellus.  Fig.  4,  the  fully 
developed  embryo  sac,  showing  the  egg  apparatus  at  the  upper  end,  the  polar  bodies  near 
the  center,  the  antipodals  at  the  bottom.  Fig.  5,  the  embryo  sac  after  fertilization,  one 
of  the  synergids  (pO  disintegrating,  the  egg  cell  at  oo,  and  8  endosperm  nuclei  (e7i)-     {After 


CHAPTER  XXVI 

THE  STRUCTURES  AND  PROCESSES  CONCERNED  IN  FRUIT 
FORMATION 

The  entire  flower  may  be  regarded  as  a  specialized  branch,  consisting 
of  a  central  axis  to  which  are  attached  several  whorls  or  sets  of  organs 
that  bear  a  certain  resemblance  to  leaves.  The  two  outer  or  lower 
whorls,  the  calyx  and  corolla,  take  no  direct  part  in  reproduction  and 
are  spoken  of  as  non-essential  organs,  though  after  fertilization  the 
calyx  may  undergo  considerable  differentiation  and  form  a  considerable 
part  of  the  mature  fruit.  As  stated  before,  the  stamens  bear  the  male 
gametes.  In  the  higher  plants,  exclusive  of  the  gymnosperms,  the  female 
gametes  are  developed  inside  an  enclosed  structure,  the  ovary.  This 
last  may  consist  of  a  single  carpel  (or  modified  leaf,  to  follow  the  concep- 
tion of  one  school  of  botanists)  or  of  several  that  are  more  or  less  com- 
pletely united.  In  the  latter  case  the  ovary  and  the  fruit  which  develops 
from  it,  may  be  several-loculed.  That  portion  of  the  central  axis  of  the 
flower  to  which  the  several  sets  of  floral  organs  are  attached  is  the  recep- 
tacle or  torus. 

A  fruit  may  be  defined  as  a  ripened  ovary  together  with  whatever 
may  be  intimately  attached  to  it  at  maturity.  If  it  consists  of  a  ripened 
ovary  only,  as  in  the  peach  or  tomato,  it  is  a  simple  fruit;  if  it  includes 
additional  structures  it  is  spoken  of  as  an  accessory  fruit.  Sometimes 
the  accessory  structure  may  be  the  torus,  as  in  the  apple;  sometimes 
the  torus  and  the  calyx,  as  in  the  cranberry  and  sometimes  a  part  of 
the  peduncle  or  pedicel,  as  in  some  varieties  of  the  pear.  The  developing 
ovaries  of  certain  fruits  grow  together  and  give  rise  (1)  to  aggregate 
fruits,  if  they  all  belonged  to  the  same  flower,  as  in  the  raspberry,  or 
(2)  to  multiple  fruits  if  they  belonged  to  different  flowers,  as  in  the 
mulberry.  In  the  latter  the  mature  fruit  includes  ovarian,  toral  and 
stem  tissues.  Not  infrequently  the  ovarian  tissues  constitute  only  a 
small  part  of  the  mature  fruit  and  as  a  rule  it  is  the  accessory  tissues 
(when  they  are  present)  in  which  the  pomologist  is  mainly  interested, 
for  they  are  likely  to  constitute  most  of  its  edible  portion.  However, 
it  is  the  ovary  with  its  enclosed  ovules  on  which  fruit  formation 
depends;  consequently  a  discussion  of  fruit  setting  and  fruit  formation 
must  start  with  the  ovary  and  its  ovules. 

The  Ovule. — The  ovule  arises  as  a  protuberance  from  the  inner  wall 
of  the  ovary.     The  particular  points,  lines  or  surfaces  from  which  it 

475 


476 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


/^.^ 


Plate  II. — Successive  stages  in  the  development  of  tlie  pollen  grain  of  the  grape. 
Fig.  1,  section  of  anther  showing  epidermal,  middle,  tapetal  and  mother-cell  layers.  Figs. 
2  and  3,  later  stages  in  these  same  layers.  Fig.  4,  a  pollen-mother-cell.  Fig.  5,  the  tetrad 
stage  in  the  pollen-mother-cell.  Fig.  6,  a  microspore  or  pollen  grain,  before  its  liberation 
from  the  pollen-mother-cell.  Fig.  7,  a  pollen  grain  of  the  Concord  grape.  Fig.  8,  the  genera- 
tive cell  in  a  mature  pollen  grain.  Figs.  9-12,  various  stages  in  the  development  of  the 
generative  and  vegetative  nuclei,  but  in  each  instance  one  or  both  nuclei  are  undergoing 
degeneration.  Fig.  13,  the  normal  generative  cell  and  vegetative  nucleus  of  a  pollen  grain. 
(After  Dorsey.^^) 


FRUIT  FORMATION  477 

springs  are  known  as  the  placentae.  Successive  stages  in  the  develop- 
ment of  a  typical  ovule  are  shown  in  Figs.  1  to  3  of  Plate  I.  The  ovules 
of  different  species  vary  greatly  in  size,  shape  and  degree  of  development 
and  differentiation.  However,  practically  all  differentiate  into  a  central 
portion  and  one  or  two  enveloping  layers.  The  central  portion  is  known 
as  the  nucellus,  the  enveloping  layers  as  the  outer  and  inner  integuments. 
These  several  structures  are  clearly  shown  in  Figs.  2  and  3  of  Plate  I. 
The  integuments  never  completely  enclose  the  nucellus  but  leave  an 
opening  of  varying  size,  the  micropyle,  through  which  the  pollen  tube 
usually  passes  to  effect  fertilization.  The  stalk  or  filament  by  which  the 
ovule  is  attached  to  the  ovarian  wall  is  known  as  the  funicle.  Through 
it  the  ovule  and  later  the  developing  seed  receives  its  supply  of  food 
material.  In  many  species  the  funicle  is  fused  with  the  outer  integument 
for  a  short  distance,  giving  rise  to  a  ridge  known  as  the  raphe.  The 
point  where  the  nucellar  and  integumental  tissues  are  continuous  and 
grown  together  is  the  chalaza. 

The  Embryo  Sac. — At  an  early  stage  in  the  development  of  the 
nucellus,  one  of  its  cells,  the  macrospore,  becomes  differentiated  from 
the  others.  This  cell  enlarges  and  divides  first  into  two  and  then  into 
four  cells  forming  the  axial  row.  The  first  division  of  the  macrospore 
mother  cell  is  the  reduction  division,  which  means  that  the  number 
of  chromosomes  in  the  nucleus  of  each  of  these  four  cells  is  half  of  the 
number  in  the  mother  cell  from  which  they  were  derived.  Ordinarily 
only  one  of  these  four  cells  develops  and  this  becomes  the  embryo  sac, 
shown  in  Fig.  3  of  Plate  I.  Its  nucleus  divides  into  two,  then  four  and 
finally  eight,  presenting  the  condition  shown  in  Fig.  4  of  Plate  I.  At  this 
stage  the  protoplasm  of  the  embryo  sac  is  highly  vacuolated.  At  one 
end,  three  of  the  nuclei  are  visible,  constituting  the  egg  apparatus.  Only 
one  is  capable  of  being  fertilized.  The  other  two  are  called  synergids; 
their  exact  function  is  not  known.  At  the  opposite  end  of  the  embryo  sac 
are  three  nuclei  called  antipodals  which  are  separated  at  an  early  stage 
from  the  rest  of  the  sac  contents  by  the  formation  of  cell  walls.  These 
cells  do  not  take  any  direct  part  in  the  process  of  fertihzation  and  they 
do  not  influence  the  development  of  the  fruit  so  far  as  known.  Sooner 
or  later  they,  like  the  synergids,  disintegrate.  Near  the  center  of  the 
embryo  sac  are  the  other  two  nuclei  called  polar  bodies  because  each  has 
come  from  the  group  of  nuclei  at  the  extreme  ends  or  poles  of  the  embryo 
sac.  These  nuclei  fuse  and  divide  rapidly,  forming  the  endosperm;  in 
many  instances  one  of  the  male  gametes  unites  with  the  fusion  nucleus 
bringing  about  double  fertilization. 

Pollen. — Stamens  originate  as  small  protuberances  at  their  points 
of  insertion  on  the  axis  of  the  flower.  At  first  these  projections  consist 
of  homogeneous  tissue,  but  differentiation  soon  occurs  and  it  becomes 
possible   to  recognize   filament  and   anther.     The  anther  increases  in 


478  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

size  more  rapidly  than  the  filament  and  gives  rise  to  a  structm^e  that  is 
generally  grooved  longitudinally  on  the  outside  and  four-loculed  in 
cross  section.  Figures  1  to  8  of  Plate  II  show  successive  stages  in  the 
development  of  the  male  reproductive  cell,  or  pollen  grain,  from  the 
tissues  of  the  anther  in  the  grape.  At  a  comparatively  early  stage  there 
is  a  differentiation  between  the  cells  of  its  outer  layers  and  those  in  the 
interior.  This  differentiation  has  progressed  rather  far  in  the  section 
shown  in  Fig.  1,  Plate  II,  the  epidermal,  middle,  tapetal  and  mother- 
cell  layers  being  clearly  distinguishable.  Eventually  the  epidermal 
and  sub-epidermal  layers  undergo  a  series  of  changes  which  lead  to 
their  separation  from  the  sporogenous  tissue  within  and  to  their  assuming 
the  role  of  a  simple  protective  shell  or  covering.  Some  idea  of  these 
changes  is  afforded  by  Figs.  2  and  3  of  Plate  II.  Figure  4  of  Plate  II 
shows  a  single  large  pollen-mother-cell  just  previous  to  the  reduction 
division,  which  gives  rise  to  four  daughter  cells,  each  of  which  is  sur- 
rounded by  a  membrane  or  cell  wall.  This  is  the  so-called  tetrad  stage, 
shown  in  Fig.  5,  Plate  II,  though  only  three  of  the  four  microspores  are 
shown  in  the  plane  in  which  that  figure  was  drawn.  Shortly  after  the 
formation  of  these  tetrads  the  mother-cell  wall  breaks  down  and  liberates 
the  microspores.  Figure  6  of  Plate  II  shows  one  of  the  microspores  of  the 
Brighton  grape  just  previous  to  its  liberation  and  Fig.  7  of  Plate  II  shows 
one  of  the  Concord  variety  a  short  time  after  its  liberation.  Its  thick 
wall,  large  nucleus  and  vacuole  are  prominent.  Usually  some  time 
before,  though  sometimes  after,  the  dehiscence  of  the  anther  and  the 
dispersal  of  the  pollen  there  are  further  changes  within  the  pollen  grain. 
The  nucleus  divides  giving  rise  to  two  daughter  nuclei.  One  is  called  the 
generative  nucleus,  because  it  alone  gives  rise  to  the  gametes.  This 
generative  nucleus  becomes  surrounded  by  a  cell  wall  and  is  then  called 
the  generative  cell  of  the  pollen  grain.  The  other  is  called  the  vegetative 
nucleus,  because  its  function  is  more  closely  associated  with  germination 
and  because  it  functions  as  the  nucleus  of  the  pollen  tube.  Figures  9 
and  12  of  Plate  II  show  two  stages  in  the  development  of  these  two  nuclei, 
though  both  cases  are  somewhat  abnormal  because  they  show  the  initial 
stages  of  a  degeneration  that  leads  to  impotency.  Figure  14  of  Plate  II 
shows  the  generative  cell  and  vegetative  nucleus  of  a  mature  pollen  grain 
of  the  Concord  grape  before  dehiscence. 

Pollination. — In  the  ordinary  course  of  events  the  maturing  of  the 
ovules  and  of  the  pollen  grains  is  followed  by  a  transfer  of  pollen  from 
stamen  to  stigma.  If  the  transfer  is  from  stamen  to  stigma  of  the  same 
flower  or  to  the  stigma  of  another  flower  on  the  same  plant,  or,  in  the 
case  of  pomological  varieties,  to  the  stigma  of  a  flower  on  any  plant  of 
the  same  variety,  the  process  is  self  pollination.  If  the  transfer  is  to 
the  flower  of  another  individual,  or,  in  the  case  of  pomological  varieties, 
to  the  flower  of  another  variety,  the  process  in  cross  pollination.    When 


FRUIT  FORMATION 


479 


Plate  III. — Fig.  1,  an  early  stage  in  the  development  of  the  normal  orange  embryo, 
showing  the  so-called  suspensor.  Figs.  2-4.  stages  in  the  development  of  the  ovule  of  the 
orange  showing  various  degenerative  changes  which  result  in  embryo  abortion;  should  the 
fruit  mature  it  would  be  seedless.     {After  Osawa.^"") 


480  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

self  pollination  is  effected  without  the  aid  of  any  outside  agency,  such 
as  wind  or  insects,  the  process  is  known  as  autogamy.  Many  of  the 
peculiarities  of  form,  structure,  color  and  odor  of  flowers  are  closely 
associated  with  means  for  securing  proper  self  or  cross  pollination. 
Some  of  the  factors  which  are  of  importance  in  aiding  or  preventing 
pollination  are  discussed  later. 

Germination  of  the  Pollen  Grain. — Pollination  is  usually  followed 
promptly  by  the  germination  of  the  pollen  grain.  This  is  brought 
about  by  the  absorption  of  water  and  various  substances  in  the  stigmatie 
fluid.  The  grain  swells  and  a  tube  is  pushed  out  through  one  of  the 
pores  in  the  outer  covering  or  extine.  The  tube  is  formed  by  the  intine 
or  inner  covering  which  pushes  out  through  the  germ  pore.  As  it  elongates 
it  penetrates  the  tissues  of  the  style  by  growing  between  the  cells  and  as  it 
advances  toward  the  ovarian  cavity  its  rate  of  growth  may  increase.  The 
styles  of  the  flowers  of  many  species  contain  rows  of  cells  that  may  be 
looked  upon  as  specialized  conducting  tissue  for  the  purpose  of  guiding  and 
facilitating  the  growth  of  the  pollen  tubes.  In  other  species  there  is 
no  evidence  of  such  tissue.  For  the  most  part  pollen  tubes  digest  their 
way  as  they  go,  by  the  secretion  of  a  pectin-digesting  enzyme.  This 
dissolves  the  middle  lamella  which  is  composed  of  pectin-like  substances 
that  hold  adjoining  cells  together  and  thus  permits  the  insertion  of  the 
pollen  tube  between  them.^"^  Green^^  has  shown  that  the  pollen 
of  many  kinds  of  plants  contains  diastase  and  some  kinds  were  found  to 
contain  invertase  as  well ;  during  the  process  of  germination  these  enzymes 
increase  in  amount.  Presumably  they  are  effective  in  rendering  available, 
for  the  nutrition  of  the  pollen  tube,  food  materials  stored  in  either  pollen 
grain  or  style.  This  assumption  is  supported  by  work  which  showed  that 
pollination  produces  a  rapid  rise  of  respiratory  activity  in  the  gynaeceum.  ^*^ 

In  Pelargonium  zonale  the  amount  of  carbon  dioxide  produced  by 
the  pollinated  flowers  is  5.8  times  greater  than  that  produced  by  the 
unpollinated  flowers,  though  most  other  cases  studied  were  somewhat 
less  extreme.  It  was  also  found  that  in  every  case  pollination  resulted 
in  some  change  in  the  respiratory  coefficient — the  ratio  of  oxygen  taken 
in  to  the  carbon  dioxide  given  off. 

Course  of  the  Pollen  Tube. — For  the  most  part,  the  growth  of  the  pollen 
tube  is-  directed  by  chemotropic  influences  supplied  by  the  tissues  of 
the  ovary,  the  ovules  and  by  the  style  and  stigma.  Miyoshi^*  sowed 
pollen  grains  on  agar  in  which  were  imbedded  pieces  of  stigma,  ovary 
and  ovules  of  different  degrees  of  development.  The  pollen  tubes  grew 
toward  the  pieces  from  the  vicinity  of  the  stigma,  but  they  were  attracted 
most  strongly  by  ovules  ready  for  fertilization,  growing  into  the  micropyle 
in  each  instance.  In  other  investigations  pieces  of  stigmatie  tissue  were 
observed  to  influence  the  direction  of  pollen  tube  growth  at  distances 
up  to  70  times  the  diameter  of  the  poUen  grain.  ^*^     Pollen  tubes  are 


FRUIT  FORMATION  481 

especially  sensitive  to  sugar  solutions,  growing  toward  them  readily. 
They  tend  to  grow  away  from  dry  air  and  "show  a  preference  for  spaces 
saturated  with  aqueous  vapour  to  such  as  are  less  humid.  "^^  Investi- 
gations of  the  mode  of  growth  of  the  pollen  tube  in  Houstonia  led  to  the 
conclusion  that  the  tissues  of  the  style  influence  its  direction  only  in  a 
passive  manner  but  that  "a  chemotactic  stimulus  originating  in  the 
egg-apparatus,  or  the  egg  itself,  is  the  chief  directive  influence,  "^^ 
Dorsey,  however,  has  found  tubes  growing  in  plum  styles  with  aborted 
ovules;  therefore  it  is  possible  that  growth  often  depends  less  on  a 
normal  egg-apparatus  than  the  work  with  Houstonia  would  indicate. 
Dorsey  found  also  that  in  the  apple  the  pollen  tube  may  grow  beyond 
the  ovule  and  down  into  the  stem.  Kerner  and  Oliver^^  state  that 
ovules  ready  for  fertilization  "attract  not  onlj^  pollen-tubes  from  pollen 
of  the  same  species,  but  of  others  far  removed  from  it  in  point  of  affinity. 
The  delicate  hyphae  of  several  mould-fungi  are  similarly  attracted." 

Time  for  Pollen  Tube  Growth. — Ordinarily  germination  of  the  pollen 
grain  occurs  promptly  after  pollination,  the  pollen  tube  grows  fairly 
rapidly  and  fertilization  occurs  within  a  period  of  1  or  2  days,  though 
the  time  may  be  expected  to  vary  with  temperature  and  other  environ- 
mental factors.  Under  favorable  conditions  there  is  an  interval  of  from 
9  to  120  hours  between  pollination  and  fertilization  in  apples,  plums 
and  cherries."'*'**^  The  very  much  slower  growth  of  Rome  pollen  tubes  in 
Rome  styles  as  compared  with  that  of  the  tubes  of  other  apple  varieties 
found  by  one  investigator^^  is  interesting  and  may  offer  an  explanation  of 
some  cases  of  self  sterility.  A  period  of  from  26  to  41  hours  has  been  re- 
ported in  the  case  of  certain  cucurbitaceous  plants,  ^^  4  days  in  one  of  the 
species  of  Gastrodia,^"^  one  month  in  Betula,  ^  several  months  in  H amamelis^^^ 
and  approximately  a  year  in  certain  of  the  oaks.-^  That  there  may  be 
a  great  variation  in  this  respect  between  closely  related  plants  is  evident 
from  the  behavior  of  the  Satsuma  orange  in  which  about  30  hours  have 
been  found  to  elapse •  between  pollination  and  fertilization,^^  while  a 
corresponding  period  of  4  weeks  has  been  reported  in  Citrus  trifoliata.^°° 

Fertilization. — In  Fig.  13  of  Plate  II  are  shown  the  vegetative 
nucleus  and  the  generative  cell  of  the  mature  pollen  grain.  During  the 
growth  of  the  pollen  tube  the  nucleus  of  the  generative  cell  divides,  giving 
rise  to  two  male  gametes,  each  consisting  of  a  nucleus  and  a  small  portion 
of  stainable  material.  The  pollen  tube,  after  entering  the  micropyle, 
penetrates  the  intervening  tissue  of  the  nucellus  and  then  enters  the 
embryo  sac.  The  following  account  of  fertilization  is  adapted  from 
Mottier's^^  description  of  the  process:  The  end  of  the  tube  may  enter 
the  sac  at  one  side  of  the  synergids,  in  which  case  only  one  of  these  cells 
is  at  once  disorganized,  the  other  retaining  its  normal  structure  for  some 
time.  This  condition  is  illustrated  in  Fig.  5,  Plate  I.  Often  it  enters 
between  the  two  synergids,  in  which  case  both  cells  disintegrate  almost 


482  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

immediately,  ''As  soon  as  the  end  of  the  pollen  tube  enters  the  embryo- 
sac  it  opens,  discharging  the  two  male  gametes  and  other  contents.  One 
of  the  male  nuclei  enters  the  egg-cell  and  applies  itself  to  the  nucleus  of 
the  egg,  while  the  other  passes  into  the  cavity  of  the  sac.  ...  It  is  pre- 
sumably the  first  male  nucleus  which  escapes  from  the  pollen  tube  that 
unites  with  the  nucleus  of  the  egg,  but  positive  proof  on  this  point  is 
wanting.  ...  As  fusion  progresses,  the  nuclei  become  quite  alike  in 
shape,  size  and  structure.  Their  membranes  gradually  disappear  at  the 
place  of  contact,  their  cavities  become  one,  and  the  resulting  fusion 
nucleus,  which  is  in  the  resting  condition,  can  scarcely  be  distinguished 
from  the  nucleus  of  an  unfecundated  egg.  The  nucleoli  finally  unite 
also."  The  fertilized  egg  cell  becomes  the  embryo  cell,  the  antecedent 
of  the  embryo. 

Secondary  Fertilization. — Attention  has  been  called  to  the  presence 
of  two  nuclei,  the  so-called  polar  nuclei,  near  the  center  of  the  mature 
embryo  sac.  These  are  shown  clearly  in  Fig.  4  of  Plate  I.  Usually  these 
two  fuse  with  the  second  sperm  nucleus  and  the  nucleus  resulting  from 
this  triple  fusion  divides  repeatedly  giving  rise  to  many  daughter  nuclei, 
shown  in  Fig.  5  of  Plate  I.  Soon  these  daughter  nuclei  are  separated  by 
the  formation  of  cell  walls,  the  resulting  tissue  being  the  antecedent  of  the 
seed  endosperm. 

Sometimes  the  second  sperm  nucleus  fuses  with  but  one  of  the  polar 
nuclei^^^  and  sometimes  it  degenerates  in  the  cytoplasm  of  the  embryo 
sac.  In  the  former  case,  the  endosperm  is  of  the  same  parentage  as  the 
embryo  beside  which  it  develops;  in  the  latter  case  it  is  built  from 
maternal  tissue  alone.  In  plants  with  albuminous  seeds,  this  results  in 
the  condition  known  as  xenia. 

Development  of  the  Embryo  and  Endosperm. — Following  the  process 
of  fertilization  the  embryo  cell  "divides  by  a  transverse  wall  into  two 
cells,  one  directed  towards  the  micropyle,  the  other  towards  the  base  of 
the  embryo  sac.  The  upper  of  these  two  cells  stretches,  and  is  repeatedly 
segmented;  thus  a  string  of  cells  is  formed,  known  as  the  suspensor,  bear- 
ing at  its  lower  extremity  the  embryo-cell,  which  gives  rise  to  the  greater 
portion  of  the  young  plant. "^'^     This  stage  is  shown  in  Fig.  1,  Plate  III. 

Coordinate  with  the  development  of  the  embryo  is  that  of  the 
endosperm.  To  be  exact,  in  most  developing  seeds  the  growth  of  the  endo- 
sperm is  at  first  more  rapid  than  that  of  the  embryo.  In  many  exal- 
buminous  seeds  there  is  a  period  of  very  rapid  growth  of  the  endosperm 
during  which  the  young  embryo  either  grows  very  slowly  or  persists  in 
a  practically  resting  stage.  This  is  followed  by  a  period  of  rapid  embryo 
development,  which  occurs  largely  at  the  expense  of  the  materials  accu- 
mulated in  the  endosperm.  The  initiation  of  this  period  of  rapid  growth 
in  the  slow  growing  or  resting  embryos  is  apparently  one  of  the  "sticking 
points"  in  the  process  of  seed  formation  and  in  many  species  it  is  very 


FRUIT  FORMATION  483 

important  in  determining  whether  or  not  the  fruit  shall  matm-e  or  fall 
prematurely. 

In  the  developing  seeds  of  most  species  the  tissues  of  the  nucellus 
disintegrate  and  their  substance  is  used  by  the  growing  endosperm  or 
embryo.  In  some  species,  however,  the  nucellar  tissues  persist  and  develop 
into  a  storage  tissue  that  can  hardly  be  distinguished  from  endosperm. 
Storage  tissue  of  such  origin  is  known  as  pcrisperm. 


THE  SETTING  OF  THE  FRUIT 

The  fertilization  process  and  the  following  segmentation  and  growth  of 
the  embryo  and  endosperm  within  the  ovule  are  accompanied  b}^  changes 
in  the  surrounding  ovary  wall  and  often  in  the  torus  and  other  adjoining 
tissues.  Most  noticeable  among  these  changes  is  a  thickening  and  an 
increase  in  size,  perhaps  with  some  change  in  color,  shape  and  position, 
so  that  it  is  evident  very  soon  after  blossoming  that  the  fruit  has  or  has 
not  "set,"  or  that  there  is  or  is  not  a  possibihty  of  its  maturing  properly 
in  due  time. 

However,  some  blossoms  do  not  set  fruit  and  sometimes  the  percentage 
that  sets  is  extremely  small.  Nothing  is  of  greater  importance  to  the 
fruit  grower  than  having  a  reasonable  percentage  of  the  blossoms  set. 
Yield,  income  and  profits  are  all  absolutely  dependent  on  what  the  tree 
does  in  this  respect  at  and  just  after  the  time  of  blossoming.  Of  course 
accidents  or  unfavorable  conditions  later  in  the  season  may  injure  or 
destroy  the  crop,  but  they  are  contingencies  with  which  the  grower  has 
greater  confidence  in  dealing  than  the  accidents  that  may  befall  at  the 
time  of  fruit  setting. 

The  term  "fruit  setting"  is  used  here  to  refer  to  the  initial  and  appreciable 
swelling  of  the  ovary  occurring  shortly  after  the  period  of  petal  fall.  It  is  gener- 
ally accompanied  by  some  thickening  of  the  pedicel  or  of  the  peduncle.  Meanwhile, 
flowers  that  have  not  "  set "  are  turning  yellow  or  withering  and  faUing  off.  After 
this  stage  is  passed  accidents  may  happen  and  the  "June  drop"  or  some  other 
"drop"  or  some  environmental  factor  may  cause  abscission;  nevertheless,  at 
least  for  the  time  being,  it  appears  as  though  fertilization  had  taken  place  and 
the  chances  are  good  for  the  fruit  maturing. 

What  Constitutes  a  Normal  Set  of  Fruit. — It  is  not  to  be  expected  that 
all  the  blossoms  will  set  fruit,  even  though  conditions  are  ideal.  In  most 
species  and  varieties  they  are  produced  in  such  profusion  that  a  total  set 
would  be  little  short  of  calamitous  for  the  grower.  He  is  more  interested 
in  obtaining  a  reasonable  number  of  specimens  of  good  marketable  size 
than  a  much  larger  number  of  a  size  for  which  there  is  little  demand. 
Furthermore,  he  prefers  a  crop  such  as  the  trees  can  mature  without 
undue  exhaustion,  for  then  he  is  surer  of  crops  the  following  years. 


484  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

The  set  that  the  grower  would  call  perfect  varies  greatly  with  species, 
variety  and  with  conditions.  In  1899,  Fletcher'*''  counted  4725  blossoms 
of  the  apple,  pear,  plum  and  apricot;  from  these  617  fruits  developed  what 
was  considered  a  full  crop  for  the  branches  on  which  they  were  borne. 
It  would  be  called  a  perfect  set  by  the  grower,  yet  the  percentage  actually 
setting  was  13.  The  setting  of  20  to  30  per  cent  of  the  blossoms  of  the 
Muscadine  grape  would  give  a  full  crop.^*  If,  however,  the  setting  of  10 
per  cent  of  the  blossoms  provides  for  a  full  crop,  a  5  per  cent  set  will 
provide  only  half  a  crop,  though  proportionally  but  a  few  more  blossoms 
drop.  In  terms  of  the  percentage  of  blossoms  setting,  then,  a  difference 
of  a  few  per  cent  may  have  a  great  effect  on  the  size  of  the  crop  so  that 
it  becomes  important  to  ascertain  the  causes  of  these  slight  differences  and 
the  methods  of  controlling  them. 

The  usual  failure  of  many  blossoms  to  set  and  mature  fruit  is  due  to 
many  factors,  the  more  important  of  which  are  discussed  later.  It 
should  be  understood,  however,  that  many  cultivated  varieties  char- 
acteristically produce  more  blossoms  than  possibly  can  mature  into  fruits 
and  that  consequently  a  certain  amount  of  dropping  is  to  be  expected. 
This  may  be  regarded  in  the  same  light  as  the  nearly  universal  abortion 
of  one  of  the  two  ovules  in  the  ovaries  of  most  stone  fruit  varieties 
or  two  of  the  three  ovaries  in  the  flower  of  the  date  palm — phenomena 
due  to  deep-seated  hereditary  causes  that  are  quite  beyond  control  by 
any  cultural  means. 

The  June  Drop  and  Other  Drops. — All  of  the  flowers  that  fail  to 
mature  fruit  do  not  drop  at  one  time  and  a  continuous  dropping  from 
the  flowering  stage  up  to  the  time  of  maturity  is  not  common.  Instead 
there  are  more  or  less  definite  periods  or  stages  when  extensive  dropping 
occurs.  The  loss  comes  in  a  series  of  waves,  varying  with  the  different 
fruits  in  number  and  in  the  length  of  time  between  them.  There  appear 
to  be  certain  "sticking  points,"  critical  periods,  through  which  each 
fruit  must  proceed  to  reach  full  maturity.  When  one  of  these  stick- 
ing points  is  safely  passed  there  is  comparatively  little  danger  of  the  fruit 
falling  before  the  next  critical  period  arrives.  Apparently  these  sticking 
points  for  fruit  setting  are  closely  correlated  with  definite  changes  in 
the  development  taking  place  in  the  embryo  and  in  the  endosperm  of  the 


Dorsey^^  has  made  a  careful  study  of  dropping  of  blossoms  and  newly-set 
fruits  in  the  plum  and  the  following  account,  adapted  from  his  report,  illustrates 
the  phenomenon  as  it  occurs  in  fruits  in  general : 

The  First  Drop. — The  first  drop  takes  place  very  soon  after  blossoming. 
Examination  of  the  pistils  of  the  flowers  dropping  at  this  time  shows  that  they 
are  defective.  In  some,  pistil  abortion  has  occurred  at  an  earlier  stage  than  in 
others  though  the  stage  at  which  it  occurs  is  quite  constant  for  each  variety. 
Pistils  show  all  degrees  of  development,  ranging  from  mere  rudiments  up  to  those 


FRUIT  FORMATION  485 

that  are  nearly  perfectly  formed.  The  more  defective  pistils  drop  earliest,  but 
all  flowers  come  into  full  bloom.  Flowers  with  defective  pistils  always  drop  at 
the  pedicel  base  and  neither  the  calyx  tube  nor  the  style  is  shed  by  abscission 
because  growth  is  not  carried  far  enough.  The  immediate  cause  of  the  dropping 
is  the  abortion  of  pistils  that  are  structurally  defective  and  cannot  function. 

The  Second  Drop. — "The  first  drop  is  followed  2  weeks  or  so  after  bloom  by 
another  distinct  wave  of  falling  pistils.  While  there  are  a  few  intergrading 
forms  between  these  two  drops,  certain  features  of  the  second  drop  separate  it 
distinctly  from  the  first.  Unlike  the  pistils  of  the  first  drop,  those  of  the  second 
have  every  external  appearance  of  being  normal.  Enlargement  up  to  a  certain 
point  takes  place  and  in  most  cases  the  calyx  tube  breaks  away  at  least  in  part 
even  though  there  is  insufficient  growth  in  the  young  plum  to  throw  it  off.  The 
style  is  not  deciduous  in  the  earliest  pistils  to  fall,  but,  like  the  calyx  tube,  drops 
in  those  which  fall  later.  .  .  .  Pistils  which  fall  in  the  second  drop,  as  in  the 
first,  absciss  at  the  pedicel  base  while  the  pistil  is  still  green,  although  the  pedicel 
has  become  light  yellow.  Yet  in  the  last  pistils  of  the  second  drop  to  fall  the 
abscission  layer  is  formed  at  the  base  of  the  ovary  and  in  some  instances  can 
be  easily  broken  off  at  this  point.    .    .    . 

"Emphasis  is  placed  upon  the  following  points.  .  .  :  (a)  the  period  of 
abscission  of  the  second  drop  extended  from  17  to  30  days  after  bloom;  (b) 
beginning  with  the  first  pistils  to  fall,  size  differences  between  those  persisting  and 
those  which  fell,  gradually  increased  with  time;  (c)  pistils  which  fell  within  the 
above-mentioned  time  limit  enlarged  only  up  to  a  certain  point ;  ((/)  those  pistils 
with  the  stigmas  snipped  before  pollination,  enlarged  before  falling,  to  a  size 
comparable  with  that  of  those  not  so  treated;  and  (e)  in  each  variety  there  was 
a  gradual  increase  in  the  size  of  the  pistils  which  fell  off.    .    .    . 

"The  condition  found  in  the  unfertilized  series  is  in  marked  contrast  with 
that  found  when  fertilization  takes  place.  As  early  as  18  days  after  bloom  the 
embryo  sac  in  which  the  egg  has  been  fertilized  extends  the  entire  length  of  the 
nucellus  to  the  chalaza,  and  a  jacket  of  endosperm,  usually  only  one  cell  thick, 
covers  the  entire  area  of  the  'dumb-bell-shaped'  sac.  With  the  completion  of 
these  changes  in  the  embryo  sac  the  embryo  may  be  no  larger  than  four  cells 
across.   .    .    . 

"It  will  be  seen  from  the  above  observations  that  all  the  evidence  shows  that 
fertihzation  has  not  occurred  in  the  pistils  which  fall  at  the  second  drop.  .  .  . 
Pollination  may  have  taken  place,  but  tube  growth  was  retarded  to  such  an 
extent  that  fertilization  was  prevented  probably  by  the  abscission  of  the  style." 

The  Third  Drop  or  June  Drop. — "Following  the  second  drop  there  is  still 
another — the  so-called  'June  drop.'  In  popular  usage  the  term  June  drop 
applies  primarily  to  the  third  drop  of  large  plums  because  they  are  much  more 
conspicuous,  but  does  not  include  the  relatively  few  which  fall  from  time  to  time, 
even  up  to  maturity ...  It  has  been  shown  that  time  and  size  of  dropping  draw 
a  relatively  sharp  line  between  the  first  and  the  second  waves  of  dropping.  Like- 
wise these  two  factors  separate  the  second  drop  from  the  third.  .  .  .  When 
fertilization  does  not  take  place  enlargement  reaches  only  a  certain  point,  the 
maximum  recorded  being  in  the  5.6  to  6.0  milUmeter  class,  while  the  mode  is 
near  3.0  millimeters.  Among  the  last  of  the  second  drop  an  occasional  ovule  is 
found  with  slight  embryo  development,  which  shows  that  there  are  connecting 


486  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

forms  between  the  second  and  third  drops  as  well  as  between  the  first  and  second. 
In  approximately  one  month  the  second  drop  is  over,  and  those  setting  have  so 
increased  in  size  as  to  place  them  in  a  distinct  size  class  from  those  which  have 
fallen.   .    .    . 

"Sections  have  been  made  of  the  embryos  of  a  large  number  of  plums  which 
fell  at  the  June  drop.  Dissections  were  also  made  of  ovules  at  various  stages  to 
determine  the  amount  of  growth  in  the  embryo.  The  general  condition  found 
may  be  summarized  as  follows:  (a)  embryo  development  started  but  growth 
stopped  at  any  time  from  the  stage  when  the  embryo  was  a  few  cells  across  to 
the  time  at  which  it  had  reached  nearly  the  mature  size;  (b)  endosperm  had  partly 
formed,  but  the  embryo  gained  the  ascendency  to  such  an  extent  that  it  was 
often  found  naked  in  the  nucellus ;  (c)  enlargement  in  the  seed  could  reach  nearly 
the  mature  size  when  fertilization  had  once  occurred,  accompanied  by  only  a 
sUght  growth  of  the  embryo.    .    .    . 

"The  status  of  development  in  the  ovule  in  the  third  drop  shows  marked 
differences  from  that  in  the  second.  Firstly,  greater  size  is  attained  than  is  ever 
found  in  the  second  drop,  and  secondly,  instead  of  there  being  disintegrating 
nuclei  within  a  slightly  elongated  embryo  sac,  tissues  cease  growing  at  various 
stages  rather  than  disintegrating.  This  latter  fact  alone  suggests  an  additional 
stimulus  absent  in  the  second  drop.    ..." 

It  is  not  known  exactly  how  many  other  fruits  have  three  distinct 
periods  in  which  blossoms  and  developing  fruits  drop.  However,  the 
sweet  cherry  has  three  such  periods;  some  varieties,  at  least,  of  the  apple 
and  pear  have  corresponding  periods  and  presumably  they  are  to  be  found 
in  a  number  of  other  fruits,  though  in  some  of  these  species  or  varieties 
they  may  be  associated  with  other  internal  and  environmental  condi- 
tions. Certain  other  fruits,  such  as  the  currant  and  the  raspberry 
show  quite  different  characteristics  in  their  fruit  setting  and  fruit  drop- 
ping. In  some,  as  the  strawberry,  the  flowers  either  set  fruit  or  fail  to  set 
and  there  is  no  later  dropping  or  abortion.  However,  the  so-called  "June 
drop,"  which  may  or  may  not  occur  in  June  and  may  correspond  either  to 
the  second  or  the  third  drop  of  the  plum  is  important  in  determining  the 
size  of  the  crop  with  most  deciduous  tree  fruits. 

Usually,  though  not  always,  the  relation  between  the  losses  incident 
to  the  successive  drops  varies  with  the  severity  of  any  one  of  them. 
Heinicke''^  points  out  that  when  the  "first"  drop  in  the  apple  is  relatively 
large  the  June  drop  is  relatively  small;  on  the  other  hand  the  June  drop 
is  heavy  if  a  comparatively  large  proportion  of  the  flowers  begin  to  form 
fruits.  This  may  vary  according  to  variety  or  with  the  conditions  under 
which  it  is  grown.  Comparable  to  this  is  the  condition  pointed  out  by 
Reed^*"  in  certain  lemon  varieties,  in  which  an  individual  flower  bud  on 
a  small  inflorescence  has  a  greater  chance  to  set  and  develop  into  a  mature 
fruit  than  one  on  a  large  inflorescence.  Napoleon  is  an  example  of  a 
sweet  cherry  variety  that,  as  grown  in  the  Pacific  northwest,  almost 
invariably    shows  a  heavy  first   drop,    a  light  to   heavy    second   drop. 


FRUIT  FORMATION  487 

depending  on  conditions,  and  an  almost  negligible  June  drop.  When 
Llewelling  is  grown  under  similar  conditions  it  usually  shows  a  fairly- 
heavy  first  drop,  a  light  second  drop  and  a  very  heavy  June  drop. 

It  is  interesting  in  this  connection  that  occasionally  certain  flowers 
of  the  cluster  do  not  set  well,  while  others  set  fruit  perfectly.  Schuster^^^ 
has  called  attention  to  this  peculiarity  in  the  flower  clusters  of  Ettersburg 
121,  a  strawberry  variety.  The  primary  flowers  of  the  cluster,  those  com- 
ing from  the  forks,  set  freely;  only  a  small  percentage  of  the  secondaries, 
those  coming  from  the  lateral  branches  of  the  peduncle,  set  fruit.  The 
case  is  not  exactly  one  of  blossom  dropping,  for  the  flowers  do  not  drop 
off;  but  it  is  at  least  in  certain  respects  comparable  to  the  first  drop 
described  by  Dorsey  for  the  plum,  though  the  pistils  do  not  appear  to  be 
defective.  Valleau^^^  found  in  some  species  and  in  certain  varieties  of  the 
strawberry  that  the  later  flowers  to  open  may  have  sterile  pistils.  He 
ascribes  this  to  a  tendency  toward  dioeciousness. 

Another  interesting  case  of  the  June  drop  or  of  a  pheuomenon  comparable 
to  it  is  found  in  the  date  pahn.  Ordinarily  by  the  end  of  June  three  partly 
grown  fruits  of  approximately  equal  size  have  developed  from  the  three  ovaries 
of  each  pistillate  flower.  If  pollination  and  fertilization  have  taken  place  two  of 
these  developing  fruits  drop  off,  leaving  a  single  one  to  mature.  On  the  other 
hand,  if  the  flowers  have  not  been  pollinated,  all  three  may  persist  and  continue 
to  grow  slowly;  they  never  reach  full  edible  maturity  and  are  without  value. 
They  are  seedless,  closely  crowded  together  and  generally  somewhat  deformed.  ^^"^ 

Fruit    Setting,    Fruitfulness    and    Fertility    Distinguished. — In    the 

preceding  discussion  the  term  "fruit  setting"  has  been  used  to  refer  both 
to  the  initial  setting  of  the  fruit  at  or  just  after  the  time  of  blossoming 
and  to  its  remaining  on  the  plant  until  maturity.  The  term  is  used  often 
in  a  somewhat  narrower  sense  to  indicate  whether  or  not  it  remains 
attached  to  the  plant  for  any  considerable  time  after  flowering  and  whether 
any  enlargement  of  the  ovary  takes  place.  Probably  in  the  case  of  the 
plum  just  described  in  detail  few  would  regard  the  fruit  as  having 
set  if  it  did  not  siyvive  the  second  drop,  but  many  would  consider  it  as 
having  set  if  it  remained  through  this  period,  even  though  abscission 
took  place  at  the  time  of  the  third  or  June  drop.  There  are  reasons  for 
refraining  from  an  attempt  to  limit  too  closely  the  meaning  and  use  of  the 
term.  However,  it  is  desirable  to  be  able  to  refer  to  definite  conditions 
that  are  exemplified  in  many  different  species.  By  common  consent  the 
term  "fruitful"  is  used  to  describe  the  plant  that  not  only  blossoms  and 
sets  fruit,  but  carries  it  through  to  maturity.  The  plant  that  is  unable  to 
do  this,  or  that  does  not  do  it,  is  "unfruitful"  or  "barren."  "Fertihty" 
indicates  ability  not  only  to  set  and  mature  fruit  but  to  develop  viable 
seeds.  Inability  to  do  this  is  described  by  the  terms  "infertility"  and 
"sterility."     Fruitfulness  and  fertility  are  not  synonymous,  for  manj^ 


488  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

fruits,  like  the  banana,  mature  their  fruits  though  they  bear  no  mature 
seeds.  This  should  be  emphasized  because  fruitful  plants  are  often 
spoken  of  as  being  fertile,  when,  as  a  matter  of  fact,  they  may  or  may  not 
be.  Fertile  plants  are  necessarily  fruitful.  Self  fruitfulness,  therefore, 
refers  to  the  ability  of  the  plant  to  mature  fruit  without  the  aid  of  pollen 
from  some  other  flower,  plant  or  variety,  as  the  case  may  be ;  self  fertility 
indicates  a  similar  ability  to  mature  viable  seed  without  the  aid  of  pollen 
from  some  other  flower,  plant  or  variety. 

Sterility  and  Unfruitfulness  Classified. — In  a  general  way  the  causes 
of  sterility,  unfruitfulness  and  of  the  failure  of  the  fruit  to  set  may  be 
grouped  in  two  main  classes — those  internal  to  the  plant  and  those  ex- 
ternal, that  concern  more  directly  its  environment.  Frequently  it  is 
difficult,  if  not  impossible,  to  differentiate  between  these  groups  of 
factors,  for  they  are  interdependent  to  an  important  extent;  nevertheless 
it  is  convenient  to  make  such  a  grouping. 

Summary. — The  essential  organs  of  the  flower  as  they  concern  fruit 
setting  and  fruit  production  are  the  pistils  and  stamens,  though  other 
parts  may  enter  into  the  structure  of  the  fruit.  The  changes  taking 
place  in  the  ovule  and  anther  just  previous  to  the  time  of  pollination  and 
fertilization  are  described  in  detail.  Pollination  is  followed  by  the  germi- 
nation of  the  pollen  grain  and  the  growth  of  the  pollen  tube,  under  the 
influence  of  chemotropic  factors,  down  the  style.  With  the  penetration 
of  the  nucellus  by  the  pollen  tube  and  the  fusion  of  one  of  the  generative 
nuclei  of  the  latter  with  the  egg  cell,  fertilization  is  complete,  though  a 
secondary  fertilization  of  one  of  the  polar  nuclei  by  the  second  generative 
nucleus  occurs  frequently.  The  embryo  results  from  the  segmentation 
and  growth  of  the  embryo  cell  and  the  endosperm  is  the  tissue  developing 
from  the  polar  nuclei.  Fertilization  is  usually  followed  by  a  growth  of 
the  surrounding  ovarian  tissues,  resulting  in  a  "setting"  of  the  fruit. 
As  a  rule  only  a  small  percentage  of  the  flowers  of  most  deciduous  fruits 
"set"  and  many  of  those  that  remain  fall  before  the  fruit  reaches 
maturity.  In  many  fruits  there  are  several  distinct  periods  of  dropping, 
these  distinct  waves  being  referred  to  as  the  first,  second  and  June  drops. 
These  periods  of  dropping  generally  are  closely  associated  with  definite 
stages  in  the  development  of  the  tissues  of  the  ovule.  Fruit  setting, 
fruitfulness  and  fertility  are  distinguished.  The  factors  responsible  for 
unfruitfulness  may  be  classified  for  convenience  into  those  which  are 
external  and  those  which  are  internal  to  the  plant. 


CHAPTER  XXVII 
UNFRUITFULNESS  ASSOCIATED  WITH  INTERNAL  FACTORS 

Stout^^"  recognizes  three  types  of  sterility  that  are  to  be  attributed 
mainly  to  internal  factors:  (1)  sterility  from  impotence,  (2)  sterility  from 
incompatibility,  (3)  sterility  from  embryo  abortion.  Sterility  from  impo- 
tence arises  when  one  or  both  of  the  sex  organs  fails  to  develop.  This  may 
be  complete,  in  which  case  either  no  flowers  or  no  sex  organs  are  formed,  or 
it  may  be  partial,  in  which  case  either  stamens  or  pistils  are  abortive. 
Sterility  from  incompatibility  arises  when,  though  the  sex  organs  are 
completely  formed,  they  fail  to  function  properly.  In  the  last  type  of 
sterility  the  gametes  are  formed  and  apparently  function  but  abortion 
of  the  developing  embryo  takes  place  before  maturity  is  reached.-  The 
same  classification  may  hold  for  the  internally  controlled  factors  with 
which  unfruitfulness  and  the  failure  to  set  fruit  are  associated.  It  may 
be  observed  that  the  sterility  due  to  impotence  represents  an  evolutionary 
tendency  in  the  group  or  species — an  evolutionary  tendency  that  finds 
immediate  expression  in  a  distribution  of  the  two  sexes  between  different 
flowers  or  branches  on  the  same  plant  or  between  different  plants.  The 
distinction  between  sterility  due  to  incompatibility  and  that  due  to 
embryo  abortion  is  drawn  in  recognition  of  the  time  or  stage  of  develop- 
ment at  which  the  male  and  female  gametes,  both  structurally  and  func- 
tionally perfect,  show  their  incompatibihty — their  inability  to  unite  or 
develop  together  to  form  a  mature  embryo. 

Perhaps  a  classification  of  the  causes  of  sterility  associated  with 
internal  factors  and  based  upon  more  fundamental  processes  would  recog- 
nize: (1)  those  due  to  evolutionary  tendencies,  mentioned  above;  (2) 
those  due  to  genetic  influences,  regardless  of  the  exact  time  or  stage  of 
development  when  the  two  kinds  of  gametes  show  their  mutual  aversion 
and  (3)  those  due  to  physiological  factors,  in  which  case  there  is  not  true 
incompatibility  but  a  failure  of  the  plant  to  provide  nutritive  conditions 
suitable  for  continued  growth.  This  last  type  of  sterility  cannot  always 
be  differentiated  clearly  from  that  due  to  environmental  factors. 

DUE  PRINCIPALLY  TO  EVOLUTIONARY  TENDENCIES 

In  nature  the  advantage  of  cross  fertilization  in  maintaining  the  vigor 
of  the  species  has  resulted  in  many  cases  in  the  development  of  certain 
characteristics  which  make  self  fertilization  difficult,  if  not  impossible. 
These  factors,  so  favorable  to  the  maintenance  of  the  species,  may,  in 

489 


490  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

cultivation,  limit  its  usefulness  and  range.  The  more  important  of 
these  characteristics,  as  they  concern  the  fruit  grower,  are  mentioned 
here. 

Imperfect  Flowers:  Dicecious  and  MoncEcious  Plants. — Most 
fruit-producing  species  bear  perfect  flowers.  There  are  some,  however, 
in  which  the  sexes  are  separated.  In  certain  species,  such  as  the  walnut 
and  pecan,  they  are  found  in  different  flowers  on  the  same  tree  or  plant; 
in  others,  such  as  the  papaya  and  sometimes  the  strawberry,  they  are 
found  on  different  plants. 

Monoecious  plants  bear  the  pistillate  and  staminate  flowers  on  the 
same  individual  and  are  always  fruitful — at  least  theoretically — and  rather 
frequently  they  are  self  fruitful.  Certainly  the  segregation  of  the  sexes 
to  separate  flowers  of  the  plant  does  not  in  itself  interfere  with  pollination, 
fruit  setting  and  fruitfulness.  Among  the  more  common  fruits  that  are 
monoecious  are  the  walnut,  pecan,  filbert  and  chestnut.  The  members  of 
the  Cucurbitacese  also  are  for  most  part  monoecious. 

Probably  the  strawberry  is  the  most  widely  grown  of  the  dioecious 
fruits.  A  comparatively  large  percentage  of  its  varieties  bear  perfect 
flowers,  but  some  of  the  best  are  pistillate.  For  many  years  after 
the  strawberry  was  introduced  into  cultivation  no  attention  was  paid  to 
the  matter  of  planting  so  as  to  secure  pollination  of  the  pistillate  varieties, 
hence  much  of  the  failure  of  the  fruit  to  set  properly  in  the  plantations  of 
a  century  ago.  It  was  not  until  the  observations  of  Nicholas  Longworth 
of  Cincinnati  were  brought  to  the  attention  of  horticulturists  generally 
in  the  fifties  that  the  unisexuality  shown  by  plants  of  this  species  attained 
recognition  and  planting  practices  were  modified  accordingly.  Experi- 
ence has  taught  long  since  that  these  pistillate  sorts  should  be  interplanted 
with  perfect  flowering  varieties.  There  are  many  strawberry  varieties 
classified  as  perfect  flowering  that  produce  only  small  amounts  of  pollen. 
These,  as  well  as  the  imperfect  sorts,  should  be  interplanted  with  good 
pollen  producers. 

The  Japanese  persimmon  or  kaki  presents  a  very  interesting  case  of 
sex  distribution.  Many  of  its  varieties,  such  as  Tanenashi,  Hyakume, 
Hachiya  and  Costata,  produce  only  pistillate  flowers  year  after  year. 
These  are  called  "pistiUate  constants"  by  Hume.^"  Certain  other  varie- 
ties bear  each  year  pistillate  flowers  and  also  some  staminate  flowers; 
these  he  designates  as  "staminate  constants."  Still  other  varieties  bear 
only  pistillate  flowers  some  seasons  and  in  other  seasons  both  pistillate 
and  staminate.  These  are  called  "staminate  sporadics."  Hume'^^  also 
records  the  occasional  appearance  of  perfect  flowers  on  trees  that  regularly 
or  occasionally  bear  staminate  flowers,  though  they  have  not  been 
found  on  plants  of  the  pistillate  constant  type.  In  other  words,  certain 
varieties  are  monoecious,  others  dioecious;  still  others  vary  from  the  one' 
condition  to  the  other  and  occasionally  a  variety  becomes  temporarily 


UNFRUITFULNESS  ASSOCIATED  WITH  INTERNAL  FACTORS  491 

perfect  flowering.  The  study  of  these  flowering  characteristics  of  the 
persimmon  and  the  ehissification  of  the  more  important  of  its  varieties 
has  done  much  to  explain  the  rather  erratic  behavior  of  this  plant  in 
fruit  setting  and  the  maturing  of  seed-bearing  or  seedless  fruits. 

Even  more  variable  is  the  distribution  of  tlie  sexes  between  different  flowers 
and  different  plants  in  the  papaya.  Higgins  and  Holf^"  recognize  13  classes  of 
trees,  depending  on  the  combination  or  separation  of  stamens  and  pistils  and  on 
form  of  the  flower  clusters,  corolla  and  fruit.  Independent  of  the  classes  based 
on  features  other  than  sex  distribution,  these  types  are: 

1.  Pure  pistillate  flowering  plants. 

2.  Pure  staminate  flowering  plants. 

3.  Plants  producing  both  staminate  and  perfect  flowers. 

4.  Plants  producing  both  staminate  and  perfect  flowers,  but  with  sterile 
pollen.     These  might  be  called  pseudo-hermaphrodite  plants. 

5.  Plants  producing  staminate  and  perfect  flowers  in  which  neither  pistils 
nor  pollen  are  fertile.     The  plants  might  be  called  sterile  hermaphrodites. 

G.  Plants  producing  staminate,  pistillate  and  perfect  flowers. 

7.  Plants  producing  pistillate  and  perfect  flowers. 

8.  Plants  producing  staminate  and  pistillate  flowers. 

Tj^pes  2  and  5  are  necessarily  unfruitful,  though  type  5  is  unfruitful  appar- 
ently because  of  incompatibiUty  rather  than  impotence,  for  the  sex  organs  are 
developed  but  non-functioning.  Types  1  and  4  are  self  unfruitful,  though  it  is 
possible  that  4  is  self  barren  because  of  incompatibility  rather  than  impotence. 
The  other  types  are  self  fruitful;  at  least  fruitfulness  is  not  impossible  because 
of  impotence.  Some  of  these  self  fruitful  types  are  dioecious,  some  are  poly- 
gamo-dicecious.  Types  1  and  2  are  by  far  the  most  common;  that  is,  the  papaya 
is  for  the  most  part  unisexual.  Consequently  in  the  average  planting  of  that 
fruit  it  is  customary  to  retain  a  few  of  the  staminate  trees  in  order  to  insure  a 
good  set  of  fruit  on  those  bearing  pistillate  flowers.  Of  course  staminate  trees 
remain  barren,  but  if  there  should  be  only  relatively  few  of  them,  they  probably 
would  be  valued  more  highly  than  an  equal  number  of  the  fruit  producers. 

The  fig  shows  a  distribution  of  its  sexes  somewhat  less  complicated  than 
the  papaya;  nevertheless  this  distribution  should  often  be  given  careful 
attention  at  the  time  of  planting.  Two  kinds  of  flower  clusters  are  borne 
by  fig  trees.  Certain  bear  pistillate  flowers  only.  The  standard  fig 
varieties  include  trees  of  this  type  exclusively.  Certain  other  trees, 
called  "caprifigs, "  produce  both  pistillate  and  staminate  flowers  within 
the  same  cluster.  As  a  rule,  the  staminate  flowers  are  borne  near  the 
"eye"  of  the  fig  and  the  pistillate  flowers  near  its  base.  Fig  trees  may 
thus  be  placed  in  two  classes  in  respect  to  sex  distribution,  dioecious  or 
unisexual  trees  and  monoecious  trees.  The  pistillate  flowering  trees 
alone  produce  the  figs  of  commerce.  The  monoecious  trees  or  caprifigs 
are  planted  only  for  the  purpose  of  furnishing  pollen  for  the  pistillate  sorts. 
Some  authorities  would  take  exception  to  certain  of  the  statements  just  made 
about  the  nature  of  fig  flowers.     Eisen^"  states   that  there  are  three  kinds  of 


492  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

flowers  on  trees  of  the  caprifig  class — pistillate,  staminate  and  gall.  The  gall 
flower  is  regarded  as  a  specialized  pistillate  that  can  harbor  the  pollen-carrying 
Blastophaga  wasp  but  cannot  develop  seed.  Rixford,"^  on  the  other  hand,  holds 
that  all  so-called  gall  flowers  are  in  reality  simple  pistillates,  not  structurally 
different  from  other  pistillate  caprifig  flowers  that  occasionally  are  pollenized, 
set  fruit  and  form  seed.  Usually  they  do  not  have  the  opportunity  to  set 
and  develop  seed  because  they  are  not  pollinated  or  because  they  are  stung  by 
the  Blastophaga  and  subsequently  become  galls. 

Eisen^o  and  many  others  recognize  a  third  kind  of  pistillate  flower  which 
they  call  ''mule"  flowers.  These  are  produced  by  most  of  those  cultivated 
varieties  which  yield  seedless  fruits.  They  are  held  to  be  somewhat  different 
in  structure  from  the  pistillates  of  such  varieties  as  the  Smyrna,  that  are  capable 
of  setting  seed.  However,  Rixford"^  has  shown  that  these  so-called  mule 
flowers  do  set  and  mature  seed  when  properly  pollinated  and  consequently 
considers  them  true  pistillates. 

Heterostyly. — It  has  been  stated  that  the  flowers  of  many  species  present 
peculiarities  of  form  and  structure,  the  main  function  of  wliich  is  to  aid  in  bringing 
together  the  male  and  female  gametes  so  that  fertilization  may  take  place  and 
reproduction  be  insured.  However,  many  of  these  peculiarities  of  form  and 
structure  are  of  such  a  nature  as  to  prevent  self  pollination  and  make  cross 
pollination  more  certain.  If  cross  pollination  does  »ot  occur,  the  plant  is  very 
likely  to  remain  unfruitful  even  though  perfect  sex  organs  have  been  developed. 

One  of  these  diversities  of  form  is  heterostyly,  a  type  of  dimorphism  in  which 
some  of  the  flowers  have  short  styles  and  long  filaments  and  other  flowers  of  the 
same  species  or  variety  have  long  styles  and  short  filaments.  The  structure 
and  arrangement  is  such  that  when  these  flowers  are  visited  by  pollen-carrying 
insects  no  self  pollination  takes  place  but  pollen  from  short  stamens  is  deposited 
upon  the  stigmas  of  the  short  pistils  and  pollen  from  the  long  stamens  is  carried 
to  the  stigmas  of  the  long  pistils.  Cross  pollination  between  two  flowers  of  the 
same  form  on  a  single  plant  may  occur,  but  the  arrangement  assures  a  consider- 
able amount  of  crossing  between  plants.  It  has  been  shown  that  when  the  pistils 
of  heterostyled  plants  are  pollenized  with  pollen  from  the  same  flowers  or  from 
other  flowers  containing  stamens  of  an  equal  height  the  union  may  be  fruitful 
but  is  likely  to  be  attended  by  varying  degrees  of  sterility. ^^  This,  however, 
introduces  the  factor  of  incompatibility,  about  which  more  is  said  later. 
Apparently  heterostyly  is  relatively  unimportant  in  determining  setting  in 
deciduous  fruits. 

Dichogamy :  Protandry  and  Protogyny. — It  has  just  been  pointed  out 
that  in  heterostyled  plants  the  sexes  are  nearly  as  completely  separated 
and  self  pollination  as  completely  prevented  as  in  monoecious  plants. 
Likewise  there  may  be  more  or  less  separation  of  the  sexes  and  a  pre- 
vention of  self  pollination  in  perfect  flowered  plants  through  the  maturing 
of  the  two  sex  elements  at  different  times.  This  behavior  of  the  plant 
is  known  as  dichogamy.  If  the  stamens  ripen  before  the  pistil  is  ready 
to  receive  pollen  the  flower  is  protogynous;  if  the  reverse  condition 
holds  it  is  protandrous.     Dichogamy  is  incomplete  when  there  is  an 


UNFRUITFULNESS  ASSOCIATED  WITH  INTERNAL  FACTORS  493 

overlapping  in  the  seasons  of  maturity  of  the  two  sex  elements;  otherwise 
it  is  complete.  Complete  dichogamy  insures  pollination  with  some  other 
flower  and  perhaps  with  another  plant.  Incomplete  dichogamy  tends 
in  that  direction,  but  still  allows  opportunity  for  a  certain  amount  of 
selfing. 

The  frequent  occurrence  of  dichogamy  and  consequently  its  impor- 
tance in  influencing  the  setting  of  fruit  is  not  generally  appreciated. 
Kerner  and  Oliver^*  state:  "  .  .  .  It  appears  that  all  species  of  plants 
whose  hermaphrodite  flowers  are  adapted  to  cross-fertilization  by  the 
relative  position  of  anthers  and  stigmas  are,  moreover,  dichogamous, 
although  this  dichogamy  may  be  of  slight  duration.  Plants  with  hetero- 
styled  flowers  are  also  dichogamous,  since  those  with  short-styled  and 
those  with  long-styled  flowers  develop  at  different  times.  .  .  .  As  far  as 
we  can  tell  at  present  all  monoecious  plants  are  protogynous.  .  .  . 
Alders  and  Birches,  Walnuts,  and  Planes,  Elms  and  Oaks,  Hazels  and 
Beeches  are  all  markedly  protogynous.  In  most  of  these  plants  .  .  .  the 
dust-like  pollen  is  not  shed  from  the  anthers  until  the  stigmas  on  the 
same  plant  have  been  matured  2  to  3  days.  Sometimes  the  interval 
between  the  ripening  of  the  sexes  is  still  greater.  The  majority  of 
dioecious  plants  are  also  protogynous."  Both  Waugh^^*  and  Dorsey^^ 
call  attention  to  the  existence  of  dichogamy  in  the  plum.  Pecan  varieties 
have  been  classified  in  two  main  groups,  those  exhibiting  dichogamy  and 
those  which  mature  their  stamens  and  pistils  simultaneously. ^-'' 

Interesting  as  illustrating  the  influence  of  dichogamy  on  fruit  setting  are 
certain  experiments  of  Wester ^^^  with  Anonas.  Flowers  of  the  cherimoya 
(Anona  cherimolia)  and  of  the  custard  apple  {A.  reticulata)  were  found  to  shed 
their  pollen  iu  the  afternoon  from  about  3:30  to  6:00.  Flowers  of  the  sugar 
apple  (.4.  squamosa)  discharge  their  pollen  from  sunrise  to  about  9:00  a.  m. 
A  few  trees  of  this  latter  species  were  found  to  shed  their  pollen  in  the  afternoon 
and  these  same  trees  did  not  shed  any  pollen  in  the  morning.  Many  pollina- 
tions were  made,  the  results  of  all  pointing  to  the  same  general  conclusion.  The 
follo^^^ng  account  of  one  of  his  experiments  illustrates  the  results  obtained: 
"...  1-43  flowers  on  one  sugar  apple  tree  were,  in  April  and  May,  1908,  pol- 
linated with  their  own  pollen  or  that  of  flowers  of  other  plants  of  the  same 
species,  41  with  pollen  of  the  cherimoya,  31  with  pollen  of  the  pond  apple,  and, 
51  flowers  with  pollen  of  the  custard  apple.  In  no  instance  did  fruit  set  where 
the  pollen  was  applied  to  the  stigma  simultaneously  with  the  discharge  of  its 
pollen;  practicallj''  all  responded  where  it  was  applied  15  to  48  hours  previous  to 
this  act,  though  here,  as  in  the  case  of  the  cherimoya,  the  tree  shed  much  of  the 
fruit  before  it  matured  OA\'ing  to  its  inability  to  carry  it  all." 

The  flower  clusters  of  the  caprifig,  the  dioecious  form  of  the  fig  tree,  afford 
an  extreme  and  very  interesting  instance  of  dichogamy.^"  The  stamens  and 
their  pollen  do  not  mature  until  shortly  before  the  ripening  of  the  fig,  when  the 
wasps  have  attained  their  maturity  in  the  gall  flowers  of  the  same  flower  clusters 
and  are  ready  to  emerge  and  enter  other  fruits  to  which  they  carry  pollen.     On 


494  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

the  other  hand  the  pistillate  flowers  of  the  fig  are  receptive  weeks,  or  even  months, 
earlier.  In  this  way  the  wasps,  carrying  the  pollen  from  one  crop  {e.g.,  the  pro- 
fichi)  of  the  fig,  enter  the  flowers  of  the  following  crop  (mammoni)  at  a  time  when 
their  stigmas  are  receptive.  It  is  possible  for  self  pollination  to  take  place  within 
the  tree,  but  there  is  at  least  a  crossing  between  two  successive  crops  of  the 
caprifig  and  there  is  often  actual  cross  pollination  between  trees  or  varieties. 

Commenting  on  the  significance  of  dichogamy  Kerner  and  Oliver^^  remark: 
"  From  these  facts  we  may  infer  that  every  dichogamous  plant  has  an  opportunity 
for  illegitimate  crossing  or  hybridization  at  the  beginning  or  end  of  its  flowering, 
and  that  dichogamy — especially  incomplete  dichogamy — is  the  most  important 
factor  in  its  production.  Of  course  this  does  not  exclude  dichogamy  from  playing 
an  important  part  in  legitimate  crossing  as  well.  On  the  whole,  however,  we 
can  maintain  the  view  that  the  separation  of  the  sexes  by  the  maturation  of  the 
sexual  organs  at  different  times  leads  to  hybridization,  while  their  separation 
in  space  promotes  legitimate  crossing.  The  fact  that  the  separation  of  the  sexes 
in  time  and  space  usually  occur  in  conjunction  harmonizes  with  this  conclusion, 
i.e.,  that  the  dioecious,  monoecious,  and  pseudo-hermaphrodite  flowers,  as  well 
as  those  hermaphrodite  flowers  whose  sexual  organs  are  separated  by  some  little 
distance,  are  in  addition  incompletely  dichogamous,  because  by  this  contrivance 
the  flowers  of  any  species  obtain  (1)  the  possibility  of  hybridization  at  the  begin- 
ning or  end  of  their  flowering  period,  and  (2)  of  legitimate  crossing  during  the 
rest  of  that  time.  This  also  explains  why  incomplete  dichogamy  is  so  much  more 
frequent  than  complete  dichogamy ;  why  there  are  no  dioecious  species  of  plants 
with  completely  dichogamous  flowers;  and  why,  if  one  ever  should  occur,  it 
would  of  necessity  soon  disappear.  Let  us  suppose  that  somewhere  or  other 
there  grows  a  species  of  Willow  with  completely  protogynous  dioecious  flowers, 
that  is  to  say,  a  species  in  which  the  female  flowers  mature  first,  and  have  ceased 
to  be  receptive  before  the  male  flowers  in  the  same  region  discharge  their  pollen. 
Hybridization  only  could  occur  in  it,  and  the  young  Willow  plants  resulting  from 
it  would  all  be  hybrids  whose  form  would  no  longer  agree  absolutely  with  that 
of  the  pistiUiferous  plant.  The  species  would  therefore  not  be  able  to  reproduce 
its  own  kind  by  its  seed,  and  it  would  leave  no  descendants  of  similar  form;  in 
other  words,  it  would  die  out." 

Data  are  not  available  as  to  the  exact  degree  of  dichogamy  char- 
acteristic of  different  species  and  varieties  of  the  deciduous  fruits ;  therefore 
it  is  impossible  to  state  accurately  the  extent  to  which  it  interferes  with 
their  self  pollination  or  to  what  extent  it  is  a  factor  in  determining  their 
fruit  setting.  Furthermore,  as  is  shown  later,  the  completeness  of 
dichogamy  varies  considerably  with  environmental  conditions.  There 
can  be  no  question,  however,  but  that  in  many  varieties  it  explains  the 
failure  of  numerous  blossoms  to  set. 

Impotence  from  Degenerating  or  Aborted  Pistils  or  Ovules. — It  is 
obvious  that,  if  the  setting  and  maturing  of  fruit  usually  depend  on  the 
union  of  two  properly  formed  sex  cells,  anything  which  occurs  to  interfere 
with  the  development  and  proper  functioning  of  either  gamete  probably 
will  result  in  unfruitfulness  or  at  least  in  sterility.     This  occurs  in  the 


UNFRUITFVLNESS  ASSOCIATED  WITH  INTERNAL  FACTORS  495 

developing  pistils  and  stamens  of  manj^  species  and  is  responsible  for 
many  failures  in  fruit  setting. 

Sometimes  degeneration  takes  the  form  of  an  abortion  of  the  entire 
pistil.  This  may  occur  early  or  comparatively  late  in  the  course  of  its 
development;  consequently  in  certain  species  there  are  pistils  in  all 
stages  from  those  very  rudimentary  and  plainly  not  functioning  to  those 
that  apparently  are  perfect  in  structure  and  ready  for  fertilization. 
Goff^'  records  this  condition  as  very  common  in  many  varieties  of  our 
native  plun>s,  and  Hodgson^^  states  that  the  same  thing  is  found  in  the 
pomegranate.  It  occurs  more  frequently  in  the  ornamental  types  of  the 
pomegranate  than  in  those  varieties  cultivated  primarily  for  their  fruit; 
in  either  case  it  is  one  of  the  main  causes  of  the  failure  of  the  fruit  to  set. 
Waugh/^*  in  a  rather  extended  study  of  the  occurrence  of  defective 
pistils  in  plums,  found  striking  differences  in  various  groups.  His 
findings  are  summarized  in  Table  1. 

Table  1. — Percentage  of  Defective  Pistils  in  Different  Groups  of  Plums 
{After  Waugh'^*) 

Domestica  group 4.3     Wayland  group 10.5 

Japanese  group 11.2     Wildgoose  group 19 . 8 

Americana  group 21 . 2     Chicasaw  group 10. 5 

Nigra  group 17.0     Hybrids  group 18.1 

Miner  group 1.9 

In  a  number  of  species  and  varieties  the  pistils  attain  their  usual  size 
and  they  contain  ovules  that  to  the  unaided  eye  appear  entirely  normal. 
However,  examination  shows  partial  or  complete  degeneration  in  the 
embryo  sac  just  prior  to  its  maturing;  therefore  fertilization  is  impossible. 
Embryo  sacs  of  the  orange  showing  degeneration  at  various  stages  in 
their  development  are  pictured  in  Figs.  2  to  4  of  Plate  III.  Sometimes 
these  degenerative  processes  set  in  early  in  the  development  of  the  ovules 
and  their  abortion  is  so  complete  that  it  is  evident  to  the  unaided  eye 
at  the  time  for  fertilization.  In  the  Unshu  and  Washington  Navel 
oranges,  however,  the  fruits  may  develop  in  spite  of  that  defect,  though 
they  are  seedless.  Embryo  sac  abortion  thus  becomes  in  certain  instances 
a  cause  of  seedlessness  rather  than  unfruitfulness.  Pistil  abortion, 
apparently  at  a  comparatively  late  stage  in  development,  has  been  found 
to  explain  the  failure  of  many  strawberry  blossoms  to  set  fruit  and  the 
production  of  "nubbins"  from  many  others. ^^^  One  of  the  two  ovules 
in  the  ovary  of  the  plum"  and  other  stone  fruits  is  often  much  sma^er 
than  the  other  at  the  time  of  flowering,  showing  that  at  least  a  part  of  the 
almost  universal  failure  of  one  of  the  ovules  to  develop  into  a  seed  is 
due  to  processes  operating  before  the  time  of  fertilization.  It  should  be 
noted  in  this  case,  as  in  many  other  fruits,  that  the  abortion  of  a  part 
of  the  ovules  of  the  flower  does  not  lead  necessarily  to  unfruitfulness. 


496  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

The  relation  of  number  or  proportion  of  seeds  to  the  holding  of  the  fruit 
is  discussed  in  another  connection. 

Impotence  of  Pollen. — It  has  long  been  known  that  many  apparently 
perfect  flowered  plants  produce  only  small  amounts  of  pollen  and  that 
occasionally  a  considerable  portion  of  that  which  is  borne  is  non-viable. 
In  fact  it  is  unusual  to  find  pollen  that  is  100  per  cent  viable.  However, 
few  data  have  been  available  as  to  the  proportion  of  the  pollen  produced 
by  ordinary  fruits  under  varying  conditions  that  is  defective  and  until 
recently  there  has  been  little  realization  of  the  importance  of  this  factor 
in  determining  fruit  setting  and  fruitfulness. 

Beach,  ^>  ^>  *  was  one  of  the  first  to  investigate  this  subject  carefully 
as  it  pertains  to  deciduous  fruits.  He  found  that  varieties  of  American 
grapes  fall  readily  into  three  classes  in  respect  to  fruitfulness  when  de- 
pendent on  their  own  pollen  for  fertilization.  These  he  called  self 
fertile,  self  sterile  and  partly  self  sterile.  The  varieties  of  the  partly 
self  sterile  group  varied  from  vineyard  to  vineyard  and  from  season  to 
season  in  their  degree  of  self  sterility,  but  those  of  the  self  fertile  group 
remained  completely  self  fertile;  likewise  those  of  the  self  sterile  group 
remained  completely  self  sterile.  Controlled  cross  pollination  experi- 
ments led  to  the  conclusion  that  the  partial  or  complete  self  sterility  of 
those  two  groups  was  not  due  to  any  defect  in  the  pistils  but  to  impotence 
in  their  pollen,  though  an  abundance  of  it  was  formed.  The  stamens  of 
the  self  fertile  varieties  were  erect,  while  those  of  the  self  sterile  sorts  were 
reflexed.  A  detailed  study  of  the  pollen  of  these  different  classes  showed 
marked  differences  in  the  shape  and  appearance  of  the  grains.^  Those 
of  the  self  fertile  varieties  were  oblong,  blunt  at  the  ends  and  quite  sym- 
metrical and  they  germinated  well ;  those  of  self  sterile  sorts  were  irregular 
in  shape  and  did  not  germinate  well.  Stamens  of  the  partly  self  sterile 
varieties  were  found  to  contain  some  good  and  some  poor  pollen. 

A  little  later  Reimer  and  Detjen^'"  reported  that  all  the  varieties  of 
the  Muscadine  grape  bear  reflexed  stamens  only  and  that  all  their  pollen 
is  defective.  Their  flowers  are  pseudo-hermaphrodites  rather  than  true 
hermaphrodites.  For  fruit  to  set  the  pistils  must  receive  pollen  from 
male  or  staminate  vines.  The  plants  of  this  species  are  essentially  dioe- 
cious. Failure  to  recognize  this  fact  has  been  responsible  for  much  of 
the  unfruitfulness  previously  encountered  in  the  culture  of  this  group  of 
grapes.  Among  the  plants  growing  wild  about  three-fourths  are  stami- 
nate and  one-fourth  pseudo-hermaphroditic  with  functional  pistils.^* 
More  recently  there  have  been  found  ^^ '  '^^  several  plants  of  this  species 
producing  true  hermaphrodite  flowers;  these  have  afforded  a  starting 
point  for  the  breeding  of  a  new  and  perfect  flowered  race  of  Muscadine 
grapes. 

Apparently  the  failure  properly  to  set  and  mature  fruit  occasionally 
found  in  European  varieties  of  grapes  is  likewise  due  at  least  partly  to 


UNFRUITFULNESS  ASSOCIATED  WITH  INTERNAL  FACTORS  497 

defective  pollen.''  This  dropping  of  grape  blossoms  or  of  the  partly 
developed  berries  in  those  of  the  Vinifera  varieties  is  commonly  known 
as  "coukire." 

Dorsey^*^  has  made  a  study  of  the  cj^tological  changes  within  the 
developing  pollen  grain  of  the  grape  leading  to,  or  associated  with, 
its  impotence.  Figm-es  9  to  11  in  Plate  II  show  something  of  the  nature 
of  these  degenerative  changes.  He  distinguishes  between  what  he  terms 
sterile  pollen  and  aborted  pollen.  In  the  former  after  true  pollen  grains 
are  formed  degeneration  occurs  in  cither  their  generative  or  vegetative 
nuclei  or  in  both.  Aborted  pollen  results  from  a  development  arrested 
at  an  earlier  stage.  The  following  quotation  from  his  report  brings  out 
the  more  important  details  of  his  investigations: 

"In  the  formation  of  the  sterile  and  fertile  pollen  of  the  grape  the  hetero- 
typic and  homotypic  divisions  and  the  divisions  of  the  microspore  nucleus  take 
place  normally.  Sterile  pollen  in  the  grape  results  from  degeneration  processes 
in  the  generative  nucleus  or  arrested  development  previous  to  mitosis  in  the 
microspore  nucleus.  Where  degeneration  begins  early  after  the  division  of  the 
microspore  nucleus,  both  the  generative  and  vegetative  nucleus  may  be  affected. 
If  the  generative  cell  is  well  organized  before  disintegration  begins  the  vegetative 
nucleus  may  remain  normal.   .    .    . 

"Aborted  microspores  occur  in  various  percentages  in  the  native  forms,  as 
well  as  in  the  cultivated  varieties.  While  in  the  end  the  result  is  the  same,  a 
distinction  should  be  made  between  aborted  and  sterile  pollen.  The  former  occurs 
in  both  sterile  and  fertile  forms  and  seems  to  be  due  to  arrested  development  soon 
after  being  Uberated  from  the  tetrad,  while  the  latter  results  from  disintegration 
processes  subsequent  to  mitosis  in  the  microspore  nucleus,  and  occurs  associated 
with  the  reflex  type  of  stamen  and  the  absence  of  the  germ  pore.     .    .    . 

"The  amount  of  aborted  pollen  which  occurs  in  the  grape  varies  much  in 
different  vines.  In  the  52  cultivated  varieties  the  average  per  cent,  of  aborted 
pollen  is  22.83,  compared  with  4.08  in  121  wild  staminate  vines  of  V.  vulpina 
and  3.70  in  50  wild  pistillate.  ...  Of  the  52  cultivated  varieties  only  10 
have  less  than  5  per  cent,  of  aborted  pollen.    .    .    . 

"The  difference  between  the  percentage  of  aborted  pollen  in  known  hybrids 
and  the  pure  forms,  among  the  cultivated  varieties,  is  only  slight.  The  average 
percent  of  aborted  pollen  from  10  vines,  of  varieties  generally  regarded  to  be 
pure  V.  labrusca,  is  23.10,  while  that  for  38  of  the  hybrid  varieties  is  24.60. 
There  are  some  instances,  however,  among  the  hybrids,  as  in  Black  Eagle,  where 
the  amount  of  aborted  pollen  is  small.   .    .    . 

"Since  aborted  pollen  occurs  in  much  the  same  relative  amounts  in  the  self 
fertile  and  self  sterile  varieties,  from  the  standpoint  of  fertilization  and  the  setting 
of  fruit  it  would  seem  that  the  aborted  pollen  is  unimportant  in  the  grape,  be- 
cause in  the  fertile  forms  there  is  still  an  abundance  of  potent  pollen.'"'^ 

It  should  not  be  inferred,  because  the  discussion  thus  far  has  been 
limited  to  the  grape,  that  sterility  or  unfruitfulness  due  to  pollen  abortion 
does  not  occur  in  other  fruits.     Pollen  abortion  is  a  common  occurrence 

32 


498  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

and  a  frequent  cause  of  unfruitfulness.  Osawa^"^  reports  irregular 
development  of  the  pollen  mother  cells  and  much  defective  pollen  in 
Daphne  odora.  Two  to  10  per  cent  of  the  pollen  of  the  mango  is  regu- 
larly defective,  i"*^  Dorsey^^  finds  pollen  abortion  common  in  the  plum, 
noting  that  in  that  fruit  the  disintegration  processes  usually  occur  after 
the  liberation  of  the  tetrad  from  the  pollen  mother  cell.  If  distinction 
is  to  be  made  between  pollen  sterility  and  pollen  abortion,  in  this  case 
as  in  the  grape,  the  defective  pollen  of  the  plum  is  sterile  rather  than 
aborted.  In  neither  the  plum  nor  the  mango,  however,  is  the  percentage 
of  defective  pollen  high  enough  to  interfere  seriously  with  the  setting  of  the 
fruit.  Pollen  abortion  has  been  reported  as  a  practically  constant  char- 
acteristic of  blackberries  in  New  England. ^^  Furthermore  it  has  been 
found  to  vary  greatly  with  the  variety  and  species.  For  instance  Ruhus 
allegheniefisis  was  found  to  have  about  96  per  cent,  while  R.  hispidus 
had  less  than  10  per  cent,  morphologically  perfect  pollen.  Between  these 
extremes  were  all  gradations.  The  higher  percentages  of  defectiveness 
were  enough  to  reduce  very  materially  the  set  of  fruit.  A  similar  condi- 
tion is  reported  in  the  strawberry. ^^^ 

Degeneration  occurs  in  nearly  all  the  pollen  mother  cells  of  the 
Washington  Navel  orange.  ^^^  ^<"'  Consequently  practically  no  mature 
and  perfect  pollen  grains  are  formed.  In  the  Unshu  variety ^°°  degen- 
eration is  not  so  general;  nevertheless  it  affects  a  large  number  of  the 
pollen  mother  cells.  In  these  two  varieties,  as  in  certain  others,  pollen 
abortion  is  not  accompanied  by  unfruitfulness  because  the  fruits  are 
capable  of  parthenocarpic  development,  but  it  is  responsible  for  partial  or 
complete  suppression  of  their  seeds. 

DUE  PRINCIPALLY  TO  GENETIC  INFLUENCES 
The  forms  of  self  sterility  and  self  unfruitfulness  discussed  up  to  this 
point  are  due  plainly  to  factors  associated  with  the  fundamental  constitu- 
tion of  the  protoplasm.  It  is  also  clear  that  sterility  due  to  these  factors 
is  inherited,  though  the  underlying  causal  agents  are  evolutionary 
tendencies  within  the  species.  Self  sterility  and  self  unfruitfulness  that 
are  to  be  attributed  more  directly  to  genetic  factors,  to  the  inheritance 
received,  are  here  discussed  under  the  headings  of  hybridity  and  incom- 
patibility. However,  it  is  impossible  to  differentiate  sharply  between 
these  two  types  of  sterility. 

East  and  Park^^  remark:  "Self-sterility  is  a  condition  determined 
by  the  inheritance  received,  but  can  develop  to  its  full  perfection  only 
under  a  favorable  environment."  In  his  study  of  fertility  in  chicory 
Stout^^^  found  that  out  of  a  total  of  101  plants  in  one  crop  which  came 
from  three  generations  of  known  self  sterile  ancestry  11  were  self  fertile 
and  90  were  self  sterile.  From  his  data  he  was  able  to  conclude  not  only 
that  self  sterility  is  inherited  but  that  in  this  species  narrow  breeding 


UNFRUITFULNESS  ASSOCIATED  WITH  INTERNAL  FACTORS  499 

is  more  likely  to  give  rise  to  self  sterile  plants  than  is  broad  breeding. 
Detjen^^  concluded  from  his  studies  with  the  Southern  dewberry  {Rubus 
trivialis)  that  not  only  is  self  sterility  in  that  species  transmitted  to  its 
pure  offspring,  but  frequently  to  its  hybrid  progeny. 

Sterility  and  Unfruitfulness  Due  to  Hybridity. — Unfruitfulness  and 
sterility  have  long  been  recognized  as  conditions  frequently  associated 
with  hyl)ridity.  Generally  the  wider  the  crossing  the  greater  is  the  degree 
of  sterility  encountered.  Many  instances  might  be  cited;  a  few  will 
suffice.  Waugh^^^  describes  a  hybrid  between  the  Troth  Early  peach  and 
the  Wildgoose  plum  that  has  been  named  the  IVIule.  It  bears  an  abun- 
dance of  flowers  but  they  are  without  pistils  or  petals.  The  stamens  are 
numerous,  but  malformed,  assuming  something  of  the  shape  and  appear- 
ance of  pistils.  The  variety  is  fairly  constant  in  its  flower  characteristics, 
completely  sterile  and  also  barren.  He  mentions  another  peach-plum 
hybrid,  known  as  the  Blackman,  with  similar  characteristics.  A  hybrid 
between  the  pear  and  the  quince,  described  under  the  name  Pyronia, 
flowers  and  fruits  freely  but  is  always  seedless.  ^^7  jj^  ^]^jg  ^g^gg  hybridity 
is  responsible  for  sterility  alone,  instead  of  sterility  and  barrenness,  as  in 
the  peach-plum  hybrids.  The  Royal  and  Paradox  walnuts,  hybrids 
between  the  Persian  and  the  California  and  Eastern  Black  respectively, 
are  almost  barren.  In  these  cases,  as  in  many  other  hybrids,  barrenness 
due  to  hybridity  is  associated  with  great  vegetative  vigor.  The  high 
percentage  of  aborted  pollen  found  in  wild  and  cultivated  blackberries  in 
New  England  is  to  be  attributed  mainly  to  a  condition  of  hybridity.  ^^ 
A  number  of  hybrids  between  Vitis  rotundifolia  and  various  species  of  the 
Euvitis  group  have  been  found  almost  completely  sterile;  this  is  attributed 
mainly  to  their  hybrid  condition. ^^     In  describing  one  of  these  V.  vinifera 


"Flowers  perfect  hermaphroditic  and  imperfect  hermaphroditic;  stamens 
upright  and  pistils  medium  large  in  the  perfect  hermaphroditic ;  stamens  reflexed 
and  pistils  well  developed  in  the  imperfect  hermaphroditic  flowers.  .  .  .  The 
pollen  in  the  perfect  hermaphroditic  flowers  is  a  mixture  of  shriveled  and  plump, 
sterile  and  fertile  grains.  The  fertihty  of  these  plump  grains  has  been  demon- 
strated in  actual  hand-made  cross  poUinations,  also  by  selfing  some  of  the  flowers. 
The  pollen  in  the  imperfect  hermaphroditic  flowers  is  all  shriveled  and  impotent. 
The  pistils  in  both  types  of  flowers  are  mostly  sterile,  only  two  from  17  perfect 
hermaphroditic  flower-clusters  having  developed  into  berries  in  1918.  The 
perfect  hermaphroditic  flowers  are  sterile  because  of  hybridization,  while  the 
imperfect  hermaphroditic  flowers  are  sterile  due  to  the  double  phenomenon  of 
hybridization  and  intersexualism  with  attendant  impotence." 

However,  abortion  of  pollen  and  of  pistils  cannot  always  or  entirely 
be  attributed  to  hybridity;  and,  conversely,  hybridity  is  not  always  a 
cause  of  unfruitfulness  or  even  of  sterility.  Many  of  the  cultivated 
American  varieties  of  the  grape  that  are  probably  pure  species  bear  some 


500  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

aborted  pollen  and,  furthermore,  many  varieties  of  known  hybrid  origin 
are  highly  self  fertile.  In  discussing  this  matter  Dorsey^**  says:  "Since 
both  fertile  and  sterile  hybrids  occur  among  the  cultivated  varieties  of 
American  grapes,  hybridity  is  not  necessarily  a  cause  of  sterility.  The 
relation  of  the  sterile  pollen  to  the  absence  of  the  germ  pore,  the  reflexed 
type  of  stamen,  and  the  tendency  toward  diceciousness,  suggest  that 
pollen  sterility  in  the  grape  is  only  a  step  toward  functional  dicliny." 
The  same  investigator^^  reports  somewhat  more  aborted  pollen  in  some 
of  the  hybrid  plum  varieties  than  in  some  of  those  of  pure  species  and  also 
a  tendency  for  the  degeneration  processes  to  start  earlier  in  the  hybrids. 

All  the  available  evidence  warrants  the  conclusion  that  the  highest 
fertility  is  correlated  with  neither  the  narrowest  nor  the  broadest  breeding 
possible. 

Incompatibility. — One  of  the  most  common  causes  of  self  unfruit- 
fulness  and  self  sterility  is  incompatibility  between  the  pollen  and  the 
ovules  of  the  same  plant  or  of  the  same  variety.  That  is,  both  the  ovules 
and  the  pollen  of  the  plant  are  fertile  in  themselves,  but  they  fail  to 
effect  conjugation.  Miiller  found  self  incompatibility  in  Oncidium  flexuo- 
sum  and  a  number  of  other  species  of  orchids.  ^^  In  some  instances  not 
only  did  the  pollen  fail  to  impregnate  the  ovule  but  its  action  was  injurious 
or  poisonous  to  the  stigmas,  causing  them  to  turn  brown  and  to  decay 
prematurely.  At  the  same  time  unpollinated  stigmas  remained  fresh. 
Those  that  were  pollinated  with  pollen  from  other  plants  showed  no  signs 
of  injury;  fertilization  took  place  and  fruit  set;  the  pollen  that  acted  so 
injuriously  upon  the  stigmas  of  its  own  flowers  functioned  perfectly  on 
other  plants.  The  same  condition  has  been  reported  in  Lobelia^^  and  as 
not  uncommon  in  Cichorium  intybus.'^^'^ 

The  self  sterility  or  self  unfruitfulness  that  has  been  reported  in  the 
apple,  88,  107  in  pears,^^;  "^  [^  ^^^  sweet  cherry,^";  ^^s  j^  the  plum,^^;  i^" 
in  dewberries  and  blackberries^^  and  in  the  almond^^^  is  probably  in  large 
part  attributable  to  incompatibility.  In  practically  all  of  the  instances 
cited  the  varieties  set  fruit  properly  when  cross  pollinated,  showing  that 
the  pistils  were  perfectly  developed  and  functional.  Furthermore  the 
pollen  from  these  same  varieties  proved  viable  and  capable  of  taking  part 
in  the  fertilization  process  and  in  yielding  mature  fruits  and  seeds  when 
it  was  applied  to  other  varieties  of  the  same  species.  Nevertheless, 
barrenness  followed  self  pollination.  However,  in  most  cases  data 
are  lacking  to  show  whether  or  not  pollination  was  followed  by  fertiliza- 
tion. It  is  possible  that  in  many  instances  fecundation  took  place  and  the 
immediate  cause  of  the  failure  of  the  fruit  to  set  or  mature  was  embryo 
abortion  at  a  later  stage.  This  has  been  mentioned  as  a  distinct  cause 
of  fruit  dropping.  It  is,  however,  in  most  cases  very  closely  related  to, 
if  it  is  not  actually  one  aspect  of,  incompatibility.  Therefore  the  self 
sterility  and  self  unfruitfulness  of  these  common  fruits  may  be  considered 


UNFRUITFULNESS  ASSOCIATED  WITH  INTERNAL  FACTORS  501 

as  due  to  incompatibility,  using  that  term  in  its  broader  sense  signifying 
that  the  normal  processes  of  fertilization  fail  somewhere  between  the 
production  of  functional  gametes  and  the  fusion  of  the  sex  cells. 

I  nterfruitf  Illness  and  Inter  fertility. — Just  as  the  terms  self  fruitfulness 
and  self  fertility  refer  to  the  ability  of  a  plant  or  a  variety  to  mature 
fruits  or  seed  with  pollen  from  its  own  flowers,  so  interfruitfulness 
and  interfertility  indicate  the  abihty  of  two  plants  or  two  varieties  to 
mature  fruits  and  seed  with  each  other's  pollen.  Varieties  that  are 
self  unfruitful  because  of  dioecism,  such  as  for  instance  pistillate  flowered 
strawberries,  figs  of  the  Smyrna  type  and  the  date  palm,  have  long  been 
known  to  be  interbarren  as  well.  Other  fruit  varieties,  such  as  many 
of  the  grapes,  that  are  self  barren,  or  partly  so,  because  of  impotent 
pollen,  have  been  recognized  as  interbarren  for  the  same  reason. ^^  Until 
comparatively  recently,  however,  it  has  been  the  rather  general  belief 
that  most  fruit  varieties  are  interfertile,  or  at  least  interfruitful,  even 
though  they  might  be  self  sterile,  provided  that  they  bear  good  pollen. 
That  is,  it  was  assumed  that  any  variety  of  apple  can  successfully 
pollenize  and  fecundate  any  other  apple  variety,  the  only  precaution 
necessary  in  planting  being  to  choose  varieties  blossoming  at  approxi- 
mately the  same  season.  .Occasional  instances  of  interunfruitfulness 
were  encountered  in  experimental  studies^"^  but  later  work  with  the  same 
varieties  in  the  same  or  in  a  different  place  often  proved  them  interfruitful 
and  the  first  results  were  regarded  as  due  to  accident  or  experimental 
error.  However,  Whitaker  and  Milton,  which  are  open  pollinated 
seedlings  of  the  Wildgoose  plum,  have  been  reported  intersterile  and 
though  both  are  fertile  when  pollinated  with  Sophie,  that  variety  is 
sterile  to  their  pollen.^" 

In  1913,  Gardner^''  reported  the  three  leading  varieties  of  the  sweet 
cherry  grown  on  the  Pacific  Coast  as  intersterile  and  interunfruitful 
in  Oregon  and  a  little  later  the  same  condition  was  reported  for  two  of 
these  varieties  in  California. '^^  At  the  same  time  all  three  varieties 
were  found  to  have  perfectly  good  pistils  and  potent  pollen.  This  is 
clearly  an  instance  of  intersterility  due  to  incompatibility.  More 
recently  several  varieties  of  the  almond  have  been  shown  to  be  inter- 
sterile in  California.  ^-^  Stout^-"  has  found  cross  incompatibility  occurring 
sporadically  in  his  pedigree  cultures  of  chicory  and  it  has  been  recorded 
in  tobacco. ^^  In  summarizing  their  observations  on  cross  incompati- 
bihty  in  tobacco.  East  and  Parks  state :^^  "Cross-sterility  in  its  nature 
identical  with  self-sterility  was  found  in  every  population  of  self-sterile 
plants  tested.  The  percentage  of  cross-sterility  in  different  populations, 
based  in  each  case  on  numerous  cross  matings,  varied  from  2.4  per  cent, 
to  100  per  cent. " 

Cross-stei'ility  is  much  less  common  than  self-sterility  but  apparently 
is  to  be  expected  in  all  those  groups  in  which  self-sterility  exists.     Data 


502  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

are  not  available  to  show  to  what  extent,  if  at  all,  the  degree  of  inter- 
unfruitfulness  can  be  modified  by  environmental  conditions  and  it  is 
not  possible  to  tell,  without  trial,  which  varieties  are  and  which  are  not 
interfruitful. 

In  Reciprocal  Crossings. — In  the  investigations  with  tobacco  to  which 
reference  has  just  been  made,  there  was  found  a  uniformity  of  behavior 
between  reciprocal  crossings. ^^  That  is,  if  a  certain  crossing  proved 
sterile,  its  reciprocal  was  likewise  sterile  and  if  one  variety  proved  incom- 
patible with  two  others,  those  two  were  likewise  sterile  to  each  other. 
On  the  other  hand,  all  grades  of  opposite  results  in  interfertility  have 
been  obtained  in  Verhascum  phceniceum  when  reciprocal  crossings  were 
made.^^^  In  some  instances  when  one  plant  was  used  as  the  male  and 
the  other  as  the  female  parent  there  was  complete  compatibility  and 
when  the  reverse  combination  was  attempted  there  was  complete  incom- 
patibility. A  similar  condition  has  been  reported  in  chicory.  ^^^  Vitis 
vinifera,  V.  bourquiniana,  V.  labrusca  and  V.  cordijolia  hybridize  freely 
with  V.  routundifolia  and  V.  munsoniana  when  the  latter  two  are  used 
as  the  pollen  parent,  but  they  hybridize  much  less  freely  when  the  re- 
ciprocal crossing  is  made.^^ 

An  interesting  case  of  interf  ruitf  ulness  of  a  reciprocal  crossing  but  of  intersteril- 
ity  when  the  crossing  was  made  one  way  and  interfertility  when  made  the  other 
appeared  in  work  done  at  the  Georgia  Experiment  Station. ^^  Flowers  of  the 
upland  cotton,  Gossypiiwi  Barbadense,  were  crossed  with  pollen  of  the  okra. 
Hibiscus  esculentns.  Perfect  cotton  bolls  were  produced  but  the  seeds  were  non- 
viable. The  reciprocal  crossing  resulted  in  normal  appearing  okra  fruits  and  in 
viable  seeds.  WeUington^'''^  secured  seedless  tomatoes  by  using  pollen  of  the 
Jerusalem  cherry,  Solanum  pseudocapsicum,  but  no  fruit  was  formed  when  the 
reciprocal  crossing  was  made. 

DUE  PRINCIPALLY  TO  PHYSIOLOGICAL  INFLUENCES 

Besides  the  effects  of  evolutionary  and  genetic  influences  in  hmiting 
the  set  of  fruit  there  are  a  number  of  others  that  can  be  conveniently 
grouped  as  physiological,  though  exact  demarcation  is  impossible. 

Unfruitfulness  Due  to  Slow  Growth  of  the  Pollen  Tube. — Closely 
related  to  the  unfruitfulness  and  the  sterility  due  to  incompatibility  is 
that  caused  by  the  very  slow  growth  of  the  pollen  tubes  in  the  style. 
Indeed,  this  may  be  considered  one  type  of  incompatibility,  due  to 
chemotropic  influences. 

Darwin^^  made  many  crossings  between  different  forms  of  heterostyled 
dimorphic  and  trimorphic  plants.  He  found  that  when  pistils  were 
pollinated  with  pollen  from  stamens  of  corresponding  height  there  was 
a  high  degree  of  fertility;  when  pollinated  from  stamens  of  a  different 
height  there  were  varying  degrees  of  sterility.  This  sterility  ranged 
from  slight  to  absolute.     Pollen  from  stamens  of  a  height  corresponding 


UNFRUITFULNESS  ASSOCIATED  WITH  INTERNAL  FACTORS  503 

to  that  of  the  stigma  (legitimate  polHnation)  placed  on  stigmas  24  hours 
after  pollination  from  stamens  of  anothcn-  height  (illegitimate  pollination) 
was  found  to  effect  fertilization,  the  earlier  applied  pollen  still  remaining 
ungerminated.  Plants  raised  from  the  few  seeds  obtained  from  illegiti- 
mate pollinations  showed  many  of  the  characteristics  of  hybrids  between 
species,  being  few  flowered,  weak  or  perhaps  profuse  flowered  and  partly 
sterile.  Practically  the  same  has  been  found  in  the  heterostyled  flowers 
of  buckwheat.  ^^^  In  the  legitimate  pollinations  less  than  18  hours 
was  required  for  the  growth  of  the  pollen  tube  and  the  fusion  of  its 
generative  cell  with  the  egg  cell  of  the  embryo  sac.  In  the  illegitimate 
pollinations  more  than  72  hours  were  necessary  for  the  same  series  of 
events.  Discussing  the  cause  of  self-sterility  in  Nicotiana  East  and  Parks 
say:^^  "...  The  immediate  difference  between  a  fertile  and  a  sterile 
combination  is  in  the  rate  of  pollen  tube  growth.  If  at  the  height  of  the 
season  a  series  of  self  pollinations  and  a  series  of  cross  pollinations  are  made 
on  a  single  plant  and  the  pistils  fixed,  sectioned  and  stained  at  intervals  of 
12  hours,  it  is  found  by  plotting  the  average  length  of  the  pollen  tubes 
in  each  pistil  against  time  in  12-hour  periods  that  the  growth  curve  of 
selfed  pollen  tubes  is  a  straight  line  which  reaches  less  than  half  the 
distance  to  the  ovary  during  the  life  of  the  flower,  while  the  curve  of 
crossed  pollen  tubes  resembles  that  of  an  autocatalysis  and  reaches  the 
ovary  in  less  than  96  hours."  Similar  differences  have  been  found  in  the 
rate  of  pollen  tube  growth  in  selfed  and  crossed  apples.*^ 

Obviously,  slow  pollen  tube  growth  alone  cannot  be  responsible  for 
a  failure  of  the  fruit  to  set,  for  eventually  the  tubes  would  reach  the 
ovules.  However,  flowers  do  not  remain  attached  to  the  flower  cluster 
or  to  the  stem  indefinitely  when  fertilization  does  not  occur.  Unless  it 
occurs  within  a  fairly  short  time,  varying  with  species,  variety  and 
environmental  conditions,  abscission  takes  place  at  the  base  of  the  style, 
ovary,  pedicel  or  peduncle  and  fruit  setting  is  prevented. 

The  failure  of  the  flowers  to  set  fruit  through  the  retarding  of  pollen 
tube  growth  by  low  temperature  is  discussed  in  another  connection. 

Premature  or  Delayed  Pollination. — Hartley^^  has  found  that  the 
flowers  of  tobacco  are  very  susceptible  to  injury  from  premature  pollina- 
tion. When  mature  pollen  grains  are  applied  to  immature  pistils  they 
germinate,  penetrate  the  styles  and  enter  the  ovules  and  if  the  ovules  are 
not  ready  for  fertilization  the  flowers  soon  fall.  In  cases  of  this  kind 
"the  separation  of  the  flower  from  the  plant  was  rapid  and  complete  and 
not  accompanied  by  any  previous  wilting  of  the  flower,  but  invariably 
occurred  at  a  j  oint  situated  at  the  base  of  the  peduncle. ' '  This  is  somewhat 
different  from  the  falling  of  flowers  from  other  causes.  Table  2  shows  the 
results  of  one  series  of  pollinations  at  various  stages  of  pistil  maturity. 
Hartley  did  not  find  any  injurious  results  from  pollinating  orange  blossoms 
nine  days  before  opening  and  but  little  injury  from  premature  polhnation 


504 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


in  the  tomato.     To  what  extent  premature  pollination  interferes  with 
the  set  of  fruit  in  the  orchard  is  unknown. 

Table  2. — Influence  op  Premature  Pollination  on  Setting  in  Tobacco 
{After  Hartleif^) 


Number  flowers 

Time  pollinated 

Per  cent  set 

20 

4 

days  before  opening 

5 

40 

3 

days  before  opening 

5 

20 

2 

days  before  opening 

0 

40 

1 

day  before  opening 

77 

20 

]/2  day  before  opening 

95 

20 

When  fully  receptive 

95 

It  is  well  known  that  if  pollination  is  long  delayed  the  blossoms  fall  without 
setting.  Kusano/''  working  with  orchids  belonging  to  the  genus  Gastrodia,  found 
that  when  pollination  was  delayed  for  2  to  3  days  fertilization  took  place  in  an 
almost  normal  manner.  When  it  was  delayed  4  days  it  was  rather  ineffective 
and  when  it  was  effective  the  resulting  fruit  varied  in  size  "according  to  the 
number  of  embryogenic  seeds."  He  also  made  the  interesting  observation  that 
when  pollination  was  delayed  3  to  4  days  a  comparatively  large  percentage  of 
the  seeds  formed  were  poly  embryonic,  while  seeds  resulting  from  earlier  pollina- 
tion seldom  contained  more  than  one  embryo. 

Nutritive  Conditions  Within  the  Plant. — There  is  abundance  of 
both  circumstantial  and  experimental  evidence  to  show  that  the  nutri- 
tive conditions  within  the  plant  at  and  just  after  the  time  of  blossoming 
are  important  in  determining  the  percentage  of  the  blossoms  that  will  set 
and  also  the  percentage  that  will  finally  reach  maturity. 

Effect  on  Pollen  Viability. — Sandsten"*  collected  pollen  from  old 
apple  trees  in  a  poor  state  of  vigor  and  at  the  same  time  from  strong  young 
trees  of  the  same  varieties  in  an  adjoining  orchard.  The  average  percent- 
age germination  of  the  first  lot  was  39.8  while  that  of  the  second  lot  was 
56.5.  The  average  number  of  hours  required  for  germination  of  the  pollen 
from  the  strong  trees  was  19.8 ;  for  that  from  the  weak  trees,  28.7.  Though 
these  differences  may  not  be  great  enough  under  average  conditions  to 
account  for  much  failure  to  set  fruit,  it  is  conceivable  that  they  may 
be  of  real  importance  under  some  conditions.  Furthermore,  it  is  possible 
that  greater  differences  frequently  exist  between  the  pollen  of  strong  and 
weak  blossoms  of  other  varieties  and  of  other  fruits. 

Effect  on  Defectiveness  of  Pistils. — Goff^^  reported  the  percentage 
of  defective  pistils  borne  by  trees  of  the  American  varieties  of  plums  and 
consequently  their  fruitfulness  to  be  closely  correlated  with  nutritive 
conditions  within  the  tree.  Exhaustion  or  weakening  one  season  by 
overbearing,  drought  or  poverty  of  soil  was  found  to  induce  the  production 
of  many  defective  pistils  the  following  spring.     He  suggested  thinning  as 


UNFRUITFULNESS  ASSOCIATED  WITH  INTERNAL  FACTORS  505 

a  preventive.  Dorsey^^  has  observed  the  same  occurrence  in  the  plum 
group  in  Minnesota.  He  mentions  two  cases 'in  particular:  "One 
variety,  Wickson,  bore  two  heavy  crops  of  crossed  plums  in  the  greenhouse 
and  the  following  year  all  pistils  were  aborted.  In  the  second  instance, 
Wolf  under  orchard  conditions  bore  heavily  in  1914,  and  for  three  con- 
secutive seasons  afterward  produced  less  than  1  per  cent  of  normal 
pistils."  Hendrickson^^  mentions  two  French  prune  trees  in  California, 
one  of  which  bore  a  heavy  and  the  other  a  hght  crop  in  1916.  In  1917  the 
conditions  of  these  two  trees  were  reversed.  Paralleling  these  alter- 
nations in  crop  yields  were  differences  in  the  actual  percentage  of  blossoms 
setting  and  maturing  fruit.  In  each  case  the  light  crop  was  due  partly 
to  a  poorer  setting  of  the  blossoms  through  exhaustion  from  heavy  bearing 
the  previous  season. 

Fruit  Setting  of  Flowers  in  Different  Positions. — Some  fruits,  like  the 
plum  and  cherry,  bear  on  both  shoots  and  spurs  and  it  is  to  be 
expected  that  slightly  different  nutritive  conditions  obtain  in  these  diff- 
erent tissues.  Dorsey"  studied  fruit  setting  of  the  plum  in  these  positions 
and  found  a  distinctly  heavier  June  drop  in  the  shoot-borne  fruits.  Some 
of  his  observations  are  particularly  interesting: 

"In  the  varieties  available  in  this  investigation^""  there  was  a  pronounced 
June  drop  in  the  plums  borne  on  the  terminal  wood.  In  fact,  on  the  older  trees 
fruit  seldom  matured  in  this  position.  The  dropping  of  fruit  from  the  terminal 
growths  can  be  partly  accounted  for  on  the  basis  of  the  competition  from  a 
thorn  or  branch  which  is  developed  between  the  lateral  fruit  buds  on  the  terminal 
twigs  the  second  season.  This  condition  occurs  over  the  entire  outer  area  of  the 
tree.  .  .  .  Under  favorable  conditions  fruit  matures  on  the  terminal  shoots, 
but  the  percentage  to  set  is  small  considering  the  mass  of  bloom,  and  even  the 
small  setting  noted  above  is  far  in  excess  of  the  usual  condition  when  there  is  a  full 
crop  on  the  remainder  of  the  tree.  It  is  apparent  that  in  this  position  competi- 
tion takes  place  between  fruit  and  branch  as  well  as  between  different  fruits."^' 

Strong  and  Weak  Spurs. — A  number  of  important  correlations  have 
been  reported  between  fruit  setting  in  the  apple  and  nutritive  conditions 
in  the  spurs  or  limb  upon  which  the  blossoms  are  borne.  ^^  As  between 
limbs  from  the  same  trees,  on  those  with  a  light  bloom  73.8  per  cent  of 
the  spurs  set  fruit,  while  on  those  with  a  heavy  bloom  only  14.1  per  cent 
set  fruit.  Of  the  spurs  on  vigorous  limbs  with  large  leaves  41.6  per  cent 
set  fruit;  15.7  per  cent  set  on  weak  limbs  with  small  leaves.  Spurs  that 
lost  all  their  flowers  and  fruit  at  the  time  of  the  first  drop  had  the  smallest 
average  number  of  flowers  (4.45)  and  those  that  flnally  set  had  the  largest 
average  (5.74).  Furthermore,  a  slightly  higher  percentage  of  the  flowers 
borne  on  spurs  with  many  flowers  actually  developed  into  fruits  than  of 
those  borne  on  spurs  with  few  flowers.  Of  2066  spurs  making  more  than 
1  centimeter  growth  in  length  in  1915,  791,  or  38.3  per  cent,  set  fruit 
in  1916;  of  3,171  spurs  making  less  than  1  centimeter  of  growth  in  length 


506 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


in  1915  only  561,  or  17.7  per  cent,  set  fruit  in  1916.  Five  hundred 
ninety-five  flower-bearing  spurs  of  several  varieties  that  set  fruit 
averaged  2.55  grams  in  weight;  760  flower-bearing  non-setting  spurs 
of  the  same  varieties  averaged  only  1.50  grams  in  weight.  Table  3  shows 
stiU  more  clearly  the  influence  of  weight  of  spur  on  its  fruitfulness.  In 
a  series  of  defoliation  experiments  Heinicke  found  that  though  50.6  per 
cent  of  the  check  spurs  set  fruit,  only  47.6  per  cent  of  those  partly  defoli- 
ated and  20.2  per  cent  of  those  completely  defoliated  set. 

Table  3. — Weight  op  Baldwin  Apple  Spurs  Holding  Fruits  Varying  Lengths 

OF  Time 

(After  Heinicke^^) 


Time  spur  held  fruit 

Number  of  spurs 

Average  weight 
in  grams 

Until  first  drop                ...        

30 

28 
30 

2  94 

Until  June  drop          

3  29 

4  27 

Evidence  Jrom  Ringing  Experiments. — Certain  plants  which  under 
ordinary  circumstances  would  not  set  and  develop  fruit  partheno- 
carpically  have  been  made  to  do  so  by  ringing  or  girdling  and  thus  leading 
to  the  accumulation  of  an  extra  store  of  food  materials  above  the  injury. 
Instances  of  this  kind  have  been  recorded  in  the  gooseberry''^  and  grape.'* 
That  ringing  often  does  not  have  such  an  influence  on  fruit  setting  is 
indicated  by  certain  experiments  with  Nicotiana.^^^  It  is  probable  how- 
ever that  ringing  has  quite  different  effects  on  various  plants  and  broad 
generalizations  cannot  be  made  from  the  available  data. 

Evidence  from  Starvation  Experiments. — Kusano^^  produced  experi- 
mentally a  series  of  extreme  nutritive  conditions  in  an  orchid  belonging  to 
Gastrodia,  at  the  time  of  fertilization  and  during  the  period  of  develop- 
ment of  the  fruit  by  partly  or  completely  separating  the  ovaries  from  their 
source  of  food.  Though  the  results  he  obtained  probably  would  not 
apply  generally  to  the  developing  fruits  of  other  species  treated  similarly, 
they  are  instructive  in  pointing  out  some  of  the  relations  existing  between 
fruitfulness,  sterility  and  nutritive  conditions.  The  following  quotations 
from  Kusano's  report  summarizes  his  findings: 

"Imperfect  or  almost  no  fruit,  but  normal  seed  with  embryo:  where  the 
normally  fertilized  flower  is  separated  from  its  nutritive  connection. 

"Imperfect  or  almost  no  fruit,  and  nearly  normal  but  embryoless  seed: 
when  the  unpoUinated  flower  is  parted  from  its  nutritive  connection ;  the  number 
of  seeds  is  exceedingly  diminished. 

"Imperfect  or  almost  no  fruit  and  seed,  but  almost  normal  embryo:  when 
the  fertilized  flower  is  subjected  to  an  extremely  unfavorable  condition  of  nutri- 


UNFRUITFULNESS  ASSOCIATED  WITH  INTERNAL  FACTORS   507 

tion.  In  this  case  the  typical  integument  is  quite  suppressed  in  development 
and  the  ovular  tissue  developed  previous  to  the  fertilization  stage  partakes  of  the 
formation  of  the  imperfect  seed-coat.   .    .    . 

"From  the  above  we  see  that  the  embryo  does  not  require  during  its  develop- 
ment the  accompaniment  of  the  normal  development  of  the  ovarial  wall  and 
the  sporophytic  ovular  tissue  and  that  the  seed-coat  alone  can  develop  com- 
pletely, independent  of  the  formation  of  the  embryo,  or  of  the  normal  develop- 
ment of  the  fruit-wall.  But  it  must  be  remembered  that  a  nutritive  condition 
which  renders  the  development  of  the  fruit-wall  unfavorable  may  bring  about  a 
small  amount  of  embryoless  seed. 

"In  the  process  of  fruitification  the  embryo  is  placed  in  the  first  rank  for 
development;  if  the  nutritive  condition  is  favorable,  it  accompanies  the  develop- 
ment of  the  seed-coat  and  fruit- wall;  if  not,  only  the  latter  portions  are  in  high 
degree  retarded  in  development.  A  similar  relation  may  exist  between  the 
fruit- wall  and  the  embryoless  seed;  under  the  condition  which  induces  most 
ovules  to  develop  into  embryoless  seeds  the  fruit-wall  develops  most  vigorously; 
under  an  insufficient  supply  of  nutritive  substances  the  number- of  the  seed- 
forming  ovules  is  diminished,  and  in  this  case  the  fruit-wall  is  sacrificed  for 
development;  in  the  extreme  case  of  an  insufficient  nutrition  both  the  fruit-wall 
and  a  larger  number  of  ovules  are  suppressed  in  development,  thereby  supplying 
limited  nutritive  material  to  a  few  ovules,  enabling  them  to  form  seed.  .  .  . 
The  development  of  the  fruit-wall  alone  under  entire  suppression  of  the  ovular 
development  is  found  in  some  instances  of  the  habitual  parthenocarpy." 

It  may  be  noted  in  passing  that  the  influences  of  the  nutritive  condi- 
tion of  the  plant  upon  fruit  setting,  fruitfulness  and  fertility  that  have 
been  pointed  out  have  been  in  part  upon  pistil  or  pollen  abortion  and  thus 
more  or  less  indirect  and  they  have  been  in  part  direct  in  apparently 
affecting  the  ability  of  the  developing  seeds  or  fruits  to  complete  their 
maturing  processes.  No  direct  or  indirect  influence  on  compatibility 
has  been  noted.  On  the  other  hand,  experimental  studies  with  chicory 
have  led  to  the  conclusion  that,  at  least  in  that  species,  "self  compati- 
bility and  self  incompatibility  operate  independently  of  the  purely 
nutritive  relations  of  the  embryos  to  their  parent  plants." ^^^ 

Summary. — The  individual  plants  of  many  species  and  likewise  many 
bud-propagated  varieties  are  self  unfruitful  because  their  flowers  are 
unisexual  and  flowers  of  but  one  sex  occur  on  a  single  plant.  Among 
deciduous  fruits  often  self  unfruitful  from  this  cause  the  kaki  or  Japanese 
persimmon  and  the  strawberry  are  the  most  familiar.  Of  more  general 
occurrence  among  fruits  is  dichogamy.  Though  seldom  complete, 
it  accounts  for  the  failure  of  many  individual  blossoms  to  set  fruit  and 
emphasizes  the  importance  of  planting  with  cross  pollination  in  mind, 
even  though  the  varieties  in  question  are  partly  self  fertile.  Heterostyly 
is  not  important  in  limiting  the  "set"  of  deciduous  fruits.  Impotence 
(partial  or  complete)  resulting  from  the  degeneration  of  pistils  or  ovules 
is    very    common    among    certain    deciduous    fruits.     Many    varieties, 


508  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

particularly  of  grapes,  produce  large  numbers  of  impotent  pollen  grains 
and  they  have  all  the  appearance  of  perfect-flowering  sorts,  though 
in  reality  they  are  pseudo-hermaphrodites.  If  the  embryo  sacs  degen- 
erate and  fruit  still  forms,  seedless  specimens  are  produced.  The  self 
sterility  of  many  varieties  is  associated  with  the  hybrid  condition  of 
the  plant.  Hybrids  between  rather  distantly  related  forms  are  likely 
to  be  self  sterile  and  often  self  unfruitful  as  well.  On  the  other  hand, 
there  is  some  evidence  that  very  narrowly  bred  varieties  or  strains  are 
rather  inclined  to  sterility.  When  sterility  is  due  to  hybridity  it  is 
likely  to  be  associated  with  pollen  or  embryo  sac  degeneration.  Incom- 
patibility is  another  cause  of  much  self  unfruitfulness.  This  is  par- 
ticularly important  in  the  apple,  pear,  plum  and  cherry.  Not  only  are 
some  varieties  self  unfruitful  but  incompatibility  exists  between  them  and 
certain  other  varieties.  This  characteristic  has  immediate  importance 
in  the  sweet  cherry  and  almond.  In  some  cases  failure  to  set  fruit 
properly  is  due  to  premature  or  delayed  pollination  or  to  a  slow  growth  of 
the  pollen  tube.  Unfavorable  nutritive  conditions  within  the  plant  are 
responsible  for  much  failure  in  fruit  setting.  Trees  that  have  been 
weakened  by  overbearing  or  other  causes  are  very  likely  to  produce 
pistils  which  are  defective  or  pollen  that  is  low  in  vitality.  There  is  often 
considerable  difference  between  flowers  borne  in  various  positions,  or 
between  those  borne  on  strong  and  weak  limbs,  in  their  abilities  to  set 
fruit. 


CHAPTER  XXVIII 
UNFRUITFULNESS  ASSOCIATED  WITH  EXTERNAL  FACTORS 

Practically  every  phase  of  the  environment  to  which  the  plant  is 
subject  just  before,  at  and  shortly  after  the  time  of  blossoming  has 
some  effect  on  fruit  setting.  The  influence  may  make  itself  felt  through 
rendering  the  plant  or  the  variety  more  or  less  completely  dichogamous, 
through  the  production  of  more  or  less  defective  pistils,  ovules,  embryo 
sacs  or  pollen  grains,  through  affecting  compatibility,  indirectly  through 
aiding  or  interfering  with  pollen  transfer  or  in  a  number  of  other  ways. 

Nutrient  Supply. — It  is  often  impossible  to  distinguish  clearly  between 
the  influence  of  nutritive  conditions  within  the  plant  and  of  conditions 
of  nutrient  supply  without  upon  fruit  setting,  fruitfulness  and  fertility. 
Though  the  nutrient  supply  available  to  the  plant  probably  acts  upon 
fruit  setting  and  development  largely  through  first  influencing  nutritive 
conditions  within,  there  are  so  many  cases  in  which  the  association 
between  the  two  is  so  evident  that  the  intervening  effect  of  the  environ- 
ment upon  nutritive  condition  within  is  overlooked.  Furthermore, 
nutritive  conditions  within  the  plant  are  controlled  more  readily  by 
affording  or  withholding  certain  nutrients  than  by  most  other  means. 
It  is  therefore  desirable  to  give  some  attention  to  nutrient  supply  as  it 
influences  fruit  setting  and  fruitfulness. 

.  Darwin"  states  that  much  manure  renders  many  kinds  of  plants 
completely  sterile.  He  cites  Gartner  as  authority  for  the  statement  that 
sterility  from  overfeeding  is  very  characteristic  in  certain  families, 
Gramineae,  Cruciferse  and  Leguminosae  being  mentioned  specially.  In 
India  Agave  vivipara  is  said  invariably  to  produce  bulbs  but  no  seeds  when 
grown  in  a  rich  soil,  though  when  it  is  grown  in  a  poor  soil  without  too 
much  moisture  the  converse  condition  holds. ^s  On  the  other  hand 
extreme  poverty  of  soil  often  leads  to  dwarfing  and  sterility,  certain  spe- 
cies of  clover  being  mentioned  particularly  in  this  connection."  Sand- 
sten^^^  found  that  excessive  feeding  of  tomatoes  caused  abnormal  flowers. 
In  some  instances  the  stamens  almost  aborted;  in  others  the  pistils  were 
greatly  thickened  and  overgrown.  There  was  a  general  tendency  for  the 
overfed  plants  to  produce  fruits  with  fewer  seeds.  Two  plants  produced 
seedless  fruits  of  normal  size.  Though  these  two  plants  produced  many 
flowers  they  set  fruit  poorly.  The  Jonathan  apple,  which  is  usually  self 
sterile  or  nearly  so  on  rich  land  in  Victoria  (Australia) ,  becomes  self 
fruitful  when  grown  on  land  of  low  productivity."     The  Hope  grape, 

509 


510  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

which  is  classified  as  a  perfect  flowered  variety  of  the  Muscadine  group, 
produces  true  hermaphrodite  flowers  only  when  given  proper  cultivation 
and  care.^^  Under  neglect  "its  pistils  gradually  cease  to  function  and 
the  vine  assumes  the  general  role  of  one  that  is  staminate."  This  is  just 
the  reverse  of  the  condition  found  in  the  Hautbois  race  of  strawberries, 
which  is  reported  as  perfect  flowered  and  productive  when  grown  under 
ordinary  culture,  though  in  a  rich  soil  the  stamens  develop  poorly  and 
produce  little  good  pollen,  the  result  being  a  poor  setting  of  fruit.  ^* 

The  data  presented  in  Table  69  of  the  section  on  Nutrition  are 
particularly  pertinent.  Applications  of  nitrate  of  soda  to  the  trees  a  week 
or  10  days  before  blossoming  increased  the  set  of  fruit  by  as  much  as  300 
per  cent  in  some  instances.  Data  are  not  available  to  show  just  how  the 
fertilizer  applications  increase  fruit  setting,  though  recent  investigations 
indicate  that  a  high  nitrogen  content  in  the  spur  itself  favors  that 
process.^^  The  results  of  these  and  similar  experiments  in  other  parts  of 
the  country  and  with  other  fruits  are  of  far  reaching  practical  importance, 
for  they  indicate  that  fruit  setting  may  be  much  more  completely  and 
directly  under  control  than  has  been  realized. 

Pruning  and  Grafting. — Pruning  and  grafting  result  in  a  changed 
environment  for  at  least  portions  of  the  plant  and  in  changed  nutritive 
conditions  within  the  entire  plant  or  within  certain  parts.  The  general 
influence  of  these  practices  on  vegetative  growth  and  fruitfulness  is 
discussed  in  some  detail  in  the  sections  on  Propagation  and  on  Prun- 
ing. In  addition  to  those  indirect  influences  on  fruit  production,  how- 
ever, they  often  have  a  more  direct  influence  on  fruit  setting.  Thus 
Darwin^^  states  that  plants  of  Passiflora  alata  as  grown  in  England  are 
generally  self  sterile.  However,  at  Taymouth  Castle  one  plant  of  this 
species  grafted  on  an  unknown  variety  became  entirely  self  fertile. 
Pinching  the  growing  tips  of  the  shoots  of  certain  European  grape  varie- 
ties when  they  are  18  to  24  inches  long  and  the  blossom  bunch  is  well 
formed  helps  materially  in  the  setting  of  the  fruit.  ^  Pruning,  along  with 
other  practices,  is  reported  to  be  one  of  the  means  of  keeping  the  Hope 
grape  (one  of  the  Muscadine  group)  in  a  true  hermaphrodite  condition. ^^ 
If  this  is  neglected  the  variety  tends  to  sterihty  through  a  weakening  and 
an  abortion  of  its  pistils.  The  Malta  orange  grafted  on  rough  lemon  or 
"khatti"  stock  in  Baluchistan  produces  fruits  averaging  16  to  17  seeds; 
when  grafted  on  the  sweet  lime  the  fruits  of  the  same  variety  average 
but  seven  seeds.  ^^  In  this  case  the  trees  have  remained  fruitful,  but 
fecundity  has  been  modified.  Though  data  on  this  question  as  it  pertains 
to  deciduous  fruits  are  almost  lacking,  there  is  reason  to  believe  that  the 
subject  is  often  of  real  importance  in  commercial  production. 

Locality. — Fruit  setting  on  trees  of  the  same  variety  is  often  much 
better  in  one  locality  than  in  another.  It  might  be  possible  to  segre- 
gate  the   various   factors    of   soil,   temperature,   humidity,  light,   etc., 


UNFRUITFULNESS  ASSOCIATED  WITH  EXTERNAL  FACTORS  511 

that  constitute  what  is  termed  locality  and  to  assign  to  each  its  portion  of 
the  total  influence  on  fruit  setting.  This,  however,  is  often  difficult  and 
from  the  grower's  standpoint  it  is  only  the  environmental  complex  and 
the  plant's  response  to  it  that  are  discernible.  Therefore  it  is  suitable 
to  make  some  mention  of  the  influence  of  localitj^  in  fruit  setting,  without 
attempting  a  detailed  analysis. 

The  common  lilac  is  said  to  bear  seeds  moderately  well  in  England 
but  in  parts  of  Germany  its  capsules  never  contain  seed.^^  The  America 
grape  has  been  found  self  sterile  in  the  Experiment  Station  grounds  at 
Columbia,  Mo.,  though  it  has  been  reported  perfectly  self  fertile  farther 
south. "2  Since  the  immediate  cause  of  self  sterility  in  the  American 
varieties  of  grape  is  of  two  general  types — pollen  abortion  and  degeneration 
in  the  generative  nucleus — locality  may  be  considered  to  have  an  influence 
on  pollen  development.  Acoinis  calmnus,  when  grown  in  certain  parts 
of  Europe,  becomes  sterile  through  the  degeneration  of  both  pollen  grains 
and  embrj^o  sacs.^*^  The  Jonathan  apple  is  often  self  sterile  in  Victoria 
( Australia), ^^  though  in  the  United  States  it  is  almost  invariably  self 
fertile.     As  self  sterility  in  the  apple  is  due  usually  to  incompatibility  or 


Table  4. — Pekcentace  of  Defective  Pistils  i\  Burbank  P 
{After  Waugh''*) 

LUM 

Source  of  flowers 

Per  cent 
defective 

Source  of  flowers 

Per  cent 
defective 

Denison,  Tex 

Santa  Rosa,  Cal 

Stark ville   Miss 

27 
0 
9 

36 

Phoenix,  Ariz 

Manhattan,  Kan 

Parry,  N.J 

5 

21 
0 

Auburn,  Ala 

embryo  abortion,  the  conclusion  seems  warranted  that  it  is  in  one  of 
these  ways  that  the  difference  between  the  localities  produces  this  dis- 
tinctive effect  on  fruitfulness. 

Still  another  way  in  which  the  factors  characteristic  of  locality  influ- 
ence fruitfulness  is  in  the  production  of  defective  pistils.  Waugh^'* 
obtained  flowers  of  the  Burbank  plum  from  different  sources  and  found 
the  percentages  of  defective  pistils  to  be  as  shown  in  Table  4.  He  found 
all  the  pistils  of  Rollingstone  defective  in  flowers  obtained  from  Minnesota 
City,  Minn.,  and  none  in  a  lot  obtained  from  Lafayette,  Ind.  He 
observed  also  that  in  some  seasons  certain  plum  varieties  were  protogyn- 
ous  in  one  locality  and  protandrous  in  another. 

A  case  in  which  self  fertilitj^  and  fruitfulness  vary  according  to  locality, 
apparently  through  some  influence  on  compatibility,  was  mentioned  by 
Darwin. ^'^  He  stated  that  "  Escholtzia  is  completely  self  sterile  in  the 
hot  climate  of  Brazil,  but  is  perfectly  fertile  there  with  the  pollen  of  any 


512  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

other  individual.  The  offspring  of  Brazihan  plants  became  in  England 
in  a  single  generation  partially  self  fertile,  and  still  more  so  in  the  second 
generation.  Conversely,  the  offspring  of  English  plants,  after  growing 
for  two  seasons  in  Brazil,  became  in  the  first  generation  quite  self  sterile." 

Season. — Just  as  it  is  almost  impossible  to  separate  the  influence  on 
fruit  setting  of  nutritive  conditions  within  the  plant  from  those  of  nutrient 
supply  without,  so  it  is  almost  impossible  to  distinguish  the  influence  of 
locality  from  that  of  season.  Seasonal  variations  at  the  same  place  may 
give  rise  to  practically  the  same  changes  in  environment  as  are  occasioned 
by  differences  in  localities  during  a  single  season.  When  this  is  true 
approximately  the  same  responses  to  the  changed  conditions  would  be 
expected.  Darwin^^  stated  that  Kolreuter  had  several  plants  of  Verhas- 
cum  phoeniceum  that  for  2  years  flowered  freely  and,  though  self  sterile, 
were  interfertile  with  other  plants, but  that  later  "assumed  a  strangely 
fluctuating  condition,  being  temporarily  sterile  on  the  male  or  female 
side,  or  on  both  sides,  and  sometimes  fertile  on  both  sides;  but  two  of  the 
plants  were  perfectly  fertile  throughout  the  summer."  Trees  of  the 
native  plum  varieties  have  been  found  to  vary  greatly  in  fertility  from 
season  to  season^^  and  a  plum  variety  that  is  protandrous  one  season 
may  be  protogynous  the  next."* 

An  interesting  case  of  a  return  of  the  potato  to  the  fertile  condition 
through  seasonal  influences  has  been  observed  in  the  Greeley  district  of 
Colorado.*^  The  Pearl  variety  as  grown  in  that  section  usually  pro- 
duces no  flowers.  During  seasons  that  are  unfavorable  for  the  normal 
development  of  the  plant  and  its  tubers,  however,  flowers  are  formed  on 
the  late  branches.  Though  ordinarily  the  blossom  buds  of  the  potato 
fall  off,  in  this  case  they  opened  but  no  pollen  was  produced.  Thus  the 
degeneracy  from  the  standpoint  of  the  potato  grower  is  accompanied  by 
some  added  development  in  the  direction  of  fruitfulness.  A  ''bastard" 
type  is  described  as  occurring  sometimes  in  the  Greeley  fields  of  this 
variety;  in  this  there  is  still  further  degeneration  of  the  tuber-bearing 
habit,  but  an  abundance  of  potent  pollen  is  produced. 

End-season  Fertility. — End-season  fertility  of  normally  self  sterile 
plants  is  rather  common.  Whitten^^^  reports  that,  "during  1897,  Ideal, 
a  hybrid  (grape)  variety,  proved  to  be  self  impotent  early  in  the  season 
but  self  potent  later  on,  the  season  being  favorable  to  a  succession  of 
bloom  throughout  the  summer."  He  states  that  since  the  vine  had 
little  fruit  to  carry,  it  made  a  vigorous  growth  and  bore  a  succession  of 
flowers.  The  appearance  of  the  self  fertile  condition  late  in  the  season 
was  accompanied  by  an  increasing  uprightness  of  the  stamens  and  pre- 
sumably with  the  formation  of  good  instead  of  sterile  pollen.  A  gradual 
decrease  in  the  percentage  of  defective  mango  pollen  has  been  noted  as 
the  season  advanced.  ^''^  East  and  Park^^  found  end-season  fertility 
developing  in  their  self  sterile  Nicotiana  plants.     In  this  case  the  imme- 


UNFRUITFULNESS  ASSOCIATED  WITH  EXTERNAL  FACTORS  513 

diate  cause  of  the  normal  self  sterility  was  a  slow  growth  of  the  pollen 
tubes,  presumably  a  result  of  chemotropic  influences;  the  appearance 
of  the  self  fertile  condition  followed  an  acceleration  in  pollen  growth. 
These  investigators  remark:  "Since  we  have  reason  to  believe  that  the 
difference  between  a  sterile  and  a  fertile  combination  in  these  plants  is  the 
ability  of  the  pollen  grain  through  something  inherent  in  its  constitution 
to  call  forth  in  the  tissue  of  the  style  in  the  former  and  not 
in  the  latter  case  a  secretion  which  accelerates  pollen-tube  growth,  it 
follows  that  in  weakened  style  tissue  some  change  has  occurred  that  renders 
this  secretion  more  easily  produced."  They  report  that  self  sterility  can 
be  restored  in  these  weakened  plants  by  allowing  them  to  go  through  a 
period  of  rest  and  then  forcing  them  into  vigorous  growth.  Their  sugges- 
tion that  "truly  self  fertile  plants  cannot  be  forced  into  self  sterility  by 
any  treatment"  obviously  holds  if  self  fertility  is  defined  to  agree  with  that 
concept.  However,  if  that  is  to  be  the  concept  of  self  fertility  it  may  be 
questioned  whether  any  of  our  cultivated  fruits  be  self  fertile.  In  the 
fruit  plantation  there  are  fruit  setting,  fruitf ulness  and  fecundity  conditions 
which  vary  with  environment. 

Contrasting  sharply  with  the  end-season  fertility  that  has  just  been 
mentioned  as  sometimes  occurring  in  the  grape,  mango  and  tobacco  is  an 
end-season  sterility  found  by  Valleau^^'^  to  be  quite  common  in  the 
strawberry. 

A  striking  example  of  seasonal  influence  on  fruit  setting  and  fruitful- 
ness  occurs  in  figs  of  the  San  Pedro  class. -^  In  varieties  of  this  group  the 
early  crop,  or  brebas,  set  freely  without  pollination,  developing  seedless 
fruits.  The  later  main  or  summer  crop  will  not  set  and  mature  without 
caprification.  This,  like  the  strawberry,  is  particularly  interesting  both 
because  it  is  an  instance  of  early  season  rather  than  late  season  fruitful- 
ness  and  because  it  is  a  constant  characteristic  of  these  varieties. 

Change  of  Sex  with  Season. — Related  to  the  influences  of  season  on 
fruit  setting,  fruitfulness  and  fertihty,  or,  more  accurately,  to  be  mentioned 
as  the  immediate  explanation  of  some  of  those  influences,  are  the  occa- 
sional effects  of  season  upon  the  complete  suppression  of  one  or  the  other 
of  the  two  sex  organs,  its  effect  upon  their  development  when  normally 
they  are  undeveloped  or  non-functional  and  its  effect  upon  change  of 
sex.  The  sweet  gale  or  bog  myrtle  {Myrica  gale)  is  a  small  shrub  which 
grows  abundantly  in  the  swamps  of  Europe,  Asia  and  North  America. 
It  is  described  by  many  authorities  as  strictly  dioecious.  However,  it  has 
been  found  that  intersexes  or  mixed  plants  of  many  gradations  are  present 
everywhere  in  the  peat  moors  of  England. ^^  Furthermore,  a  .study  of 
individual  plants  for  a  series  of  years  showed  that  changes  of  sex  occurred 
from  year  to  year.  Plants  entirely  female  in  1913  were  entirely  male  in 
1914.  Plants  female  in  1913  were  mixed  in  1914,  entirely  male  or  nearly 
all  male  in  1915  and  again  female  in  1916.     There  is  a  record  of  a  hybrid 


514  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

grape  vine  (F.  riparia  X  V.  labrusca)  which  fruited  only  twice  during  a 
30-ycar  period,  "the  pistils  evidently  varying  in  strength  but  being  gener- 
ally too  weak  to  produce  fruit.  "^  Though  the  date  palm  is  usually 
monoecious,  still  a  tree  that  ordinarily  produces  pistillate  flowers  only  may 
develop  occasionally  a  cluster  of  staminate  flowers,  or  perhaps  one  year 
produce  a  few  hermaphrodite  flowers  and  never  do  so  again.  ^^^  Certain 
varieties  of  the  Japanese  persimmon  show  great  variation  in  the  kinds 
of  flowers  they  bear  from  year  to  year. 2";  ^o  jj^  some  seasons  they 
produce  pistillate  flowers  only  and  in  other  seasons  they  produce  a  num- 
ber of  staminate  flowers  along  with  the  pistillates.  "Seedling  (per- 
simmon) trees  are  very  unreliable  in  the  production  of  blossoms,  bearing 
male  flowers  during  the  first  few  years,  then  a  small  proportion  of  female 
flowers,  while  later  the  appearance  of  male  flowers  is  sporadic  on  some 
trees  and  regular  on  others.  "2" 

Age  and  Vigor  of  Plant. — Practically  inseparable  from  the  influences 
on  fruit  setting  of  nutritive  conditions  within  the  plant,  of  nutrient 
supply  without,  of  locality  and  of  season,  is  that  of  age  and  vigor.  The 
change  from  the  production  of  staminate  flowers  only  to  that  of  some 
staminate  and  some  pistillate  flowers  and  later  of  pistillate  flowers  only, 
mentioned  in  a  preceding  paragraph  as  common  in  seedlings  of  the 
Japanese  persimmon,  is  a  case  in  point.  Young  vigorous  apple  trees 
often  fail  to  set  fruit  under  controfled  cross  pollinations,  when  older  and 
less  vigorous  trees  of  the  same  varieties  set  freely. ^"'^  Waugh^^*  found  on 
the  average  a  higher  percentage  of  defective  pistils  in  young  and  vigorous 
plum  trees  than  in  older  trees  of  the  same  kinds.  The  Muscat  of  Alex- 
andria grape  is  reported  to  show  marked  susceptibility  to  "coulure"  or 
dropping  for  the  year  or  two  after  starting  to  bear,  but  later  this  trouble 
is  much  less  serious.^  Young  grape  vines  have  been  found  to  produce 
less  pollen  than  mature  vines  of  the  same  variety.^ 

In  the  instances  cited,  age  of  plant  has  been  the  factor  apparently 
associated  with  the  degree  or  percentage  of  fruit  setting.  It  is  probable, 
however,  that  age  is  effective  through  its  influence  on  vigor  and  the 
internal  conditions  of  nutrition  or  hybridity  with  which  vigor  is  asso- 
ciated. It  is  interesting  that  Stout  found  self  compatibility  in  chicory 
entirely  independent  of  differences  in  vegetative  vigor,  thus  suggesting 
that  some  of  the  internal  factors  controlling  fruit  setting  and  fertility  are 
not  influenced  by  vigor.  As  in  the  cases  where  fruitfulness  is  influenced 
by  variations  in  nutritive  conditions,  nutrient  supply,  locality  and  season, 
most  of  the  influence  of  varying  age  and  vigor  seems  to  be  through 
effects  on  impotence  preceding  fertilization  and  embryo  abortion  at  a 
later  stage  and  not  on  compatibility,  using  that  term  in  its  narrower 
sense. 

Temperature. — The  general  effect  on  the  setting  of  fruit  of  tempera- 
tures slightly  below  freezing  just  before,  at  or  shortly  after  blossoming  is 


UNFRUITFULNESS  ASSOCIATED  WITH  EXTERNAL  FACTORS  515 

well  known  and  in  the  section  on  Temperature  Relations  is  a  some- 
what detailed  account  of  the  more  important  factors  in  frost  occurrence 
and  their  bearing  upon  fruit  production.  However,  temperatures  well 
above  the  freezing  point  often  are  important  in  determining  the  setting 
of  fruit.  Darwin^s  calls  attention  to  the  rather  common  failure  of 
European  vegetables  to  develop  fruits  and  seeds  when  grown  in  India  and 
attributes  this  failure  to  the  hot  climate  of  that  country.  In  some  of 
these  instances  the  influence  of  temperature  may  be  more  directly  upon 
the  formation  of  flower  buds  and  flower  parts  than  upon  the  processes  of 
fruit  setting. 

Goff^^  has  shown  that  though  pollen  of  most  deciduous  "fruits,  like 
the  plum,  cherry,  apple  and  pear,  germinates  freely  at  temperatures  of 
50°F.  or  above,  the  process  is  practically  inhibited  by  temperatures  of 
40°F.  or  lower.  In  a  number  of  plums  the  stigma  is  receptive  for  a 
period  of  only  4  to  6  days.  The  abscission  of  the  style  occurs  in  from 
8  to  12  days  after  bloom  and  it  is  not  influenced  to  any  great  extent  by 
temperature.^^  On  the  other  hand,  the  period  required  for  the  germina- 
tion of  the  pollen  grain  and  its  penetration  of  the  style  may  depend  on 
temperature  and  may  be  as  short  as  4  days  and  as  long  as  12.  A  period 
of  cool,  but  frostless,  weather  during  blossoming,  therefore,  may  prac- 
tically prevent  fertilization  and  thus  very  materially  limit  the  set  of  fruit. 
Presumably  similar  conditions  are  found  in  many  other  fruits,  though 
the  relative  importance  of  this  factor  varies  greatly  with  different 
species  and  varieties. 

In  this  connection  mention  should  be  made  of  the  indirect  influence 
of  temperature  on  fruit  setting  through  its  effect  on  the  activity  of  pollen- 
carrying  insects.  Evidently  the  temperature  at  which  bees  and  other 
pollen-carrying  insects  will  work  depends  on  conditions,  for  40°F.  has 
been  given  as  the  lowest  temperature  at  which  the  honey  bee  will  take 
flight^^  though  normally  they  do  not  leave  the  hive  until  the  temperature 
reaches  about  60°F.,  except  after  a  considerable  period  of  confinement. 
Whatever  the  exact  temperature  may  be,  it  is  evident  that  should  all 
other  conditions  be  favorable  a  continued  period  during  blossoming  well 
above  freezing  but  still  too  low  for  much  activity  of  the  pollen-carrying 
insects  may  account  for  many  failures  in  fruit  setting. 

An  interesting  example  of  the  influence  of  temperature  on  fruit  setting  is 
furnished  by  the  papaya.  Though  usually  a  strictly  monoecious  plant,  the 
"male"  form  sometimes  bears  fruit  in  cool  climates.  In  commenting  on  the 
change  of  sex  here  involved  Higgins  and  Holt  remark:  ^^  "This  'fruiting  of  the 
male  papaya'  takes  place  most  freely  in  cool  climates  outside  the  tropics  or  at 
high  altitudes.  In  Hawaii  it  may  be  seen  that  these  trees  fruit  more  abund- 
antly on  the  mountains  than  near  the  sea  level.  Information  received  by  cor- 
respondence with  experiment  stations  and  botanic  gardens  in  many  parts  of  the 
world,  in  reply  to  direct  inquiry,  have  confirmed  this  conclusion.     In  torrid  cli- 


516  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

mates  the  fruiting  of  the  male  is  rare.  It  is  to  be  remembered  in  this  connection 
that  all  the  staminate  flowers  of  the  male  trees  possess  an  undeveloped  or  an 
abortive  pistil.  The  only  change  in  the  cases  mentioned  consists  in  the  develop- 
ment of  this  pistil." 

Light. — It  is  doubtful  if  variations  in  light  supply  are  important 
with  deciduous  fruits.  However,  it  is  of  some  interest  that  the  willow- 
herb  (Epilobiu7n  angustifolium)  develops  its  flowers  normally  and  sets 
fruit  and  seed  freely  in  open  sunny  situations  but  when  shaded  its  flower 
buds  abort  and  fall  off  before  opening. ^^  In  fact,  this  is  true  of  many 
plants. 

Disturbed  Water  Relations. — In  the  section  on  Water  Relations 
it  is  shown  that  conditions  of  low  atmospheric  humidity,  high  tempera- 
ture, exposure  to  high  winds  and  a  limited  supply  of  soil  moisture  some- 
times induce  in  trees  moisture  deficits  that  lead  to  the  formation  of  an 
abscission  layer  and  the  dropping  of  the  blossoms  or  fruits.  The  water 
loss  in  developing  Washington  Navel  orange  fruits  at  and  shortly  after 
midday  has  been  shown  to  be  as  much  as  30  per  cent.^^  Practically  the 
same  conditions  have  been  found  responsible  for  much  of  the  shedding 
of  the  developing  bolls  in  cotton.*^  Studies  of  boll  abscission  in  cotton, 
however,  led  to  the  conclusion  that  the  water  deficit  in  the  leaves  and 
stems  was  only  indirectly  the  cause  of  abscission  since  the  water  deficit 
produced  in  the  tissues  a  rise  in  temperature  which  was  "the  stimulus 
which  directly  leads  to  abscission." 

The  dropping  of  flowers  or  partly  developed  fruits  that  is  due  to 
water  deficits  is  partly  under  control.  Irrigation,  tillage,  the  use  of 
certain  cover  crops  and  windbreaks  are  among  the  more  important 
means  that  tend  to  lessen  the  difference  between  absorption  and  trans- 
piration in  times  of  stress. 

Discussing  the  shedding  of  cotton  balls  because  of  water  deficits  Floyd  ex- 
plains how  a  surplus  of  water  may  act  in  the  same  way.     He  says: 

"If  the  general  conclusion  that  the  grand  march  of  shedding  is  due  to  the 
depletion  of  moisture  in  the  deeper  soil  be  true,  irrigation  and  better  soil  manipu- 
lation are  indicated  as  remedies.  It  has  been  shown  experimentally  by  Barre, 
in  South  Carolina,  that  irrigation  has  the  effect  of  inhibiting  shedding.  The 
observations  of  Balls  that  the  rise  of  the  water  table  in  Egypt  due  to  the  Nile 
floods,  by  asphyxiating  the  deeper  roots  and  so  limiting  the  water  supply,  causes 
severe  shedding,  are  quite  in  harmony  with  the  above  findings,  since  too  much 
water  may  have  quite  the  same  effect  as  too  little,  and  suitable  drainage  is  thereby 
indicated  as  surely  as  irrigation. "^^ 

Not  only  may  a  water  deficit  lead  to  the  dropping  of  flowers  and  newly 
set  fruits,  but  it  has  been  shown  experimentally  that  very  high  atmos- 
pheric humidity  tends  to  cause  the  abscission  of  partly  developed  apples.^' 

Rain  at  Blossoming. — Rain  at  blossoming  is  recognized  generally 
as  one  of  the  most  important  factors  Umiting  the  set  of  fruit. 


UNFRUITFULNESS  ASSOCIATED  WITH  EXTERNAL  FACTORS  517 

The  following  regarding  weather  conditions  at  blossoming  time  in  New 
York  verifies  this  statement;*"  "Wet  weather  almost  wholly  prevented  the 
setting  of  fruit  in  New  York  in  the  years  1881,  1882,  1883,  1886,  1890,  1892  and 
1901.  Rain  is  mentioned  as  one  of  the  causes  of  a  poor  setting  of  fruit  in  the 
years  1888,  1889,  1891,  1893,  1894,  1898,  1905.  .  .  .  Rain  and  the  cold 
and  wind  that  usually  accompanj'  it  at  blossoming  time  cause  the  loss  of  more 
fruit  than  any  other  cUmatal  agencies.  The  damage  is  done  in  several  ways. 
The  most  obvious  injury  is  the  washing  of  the  pollen  from  the  anthers.  The 
secretion  on  the  stigmas  also  is  often  washed  away  or  becomes  so  diluted  that  the 
pollen  does  not  germinate.  It  is  probable  that  the  chill  of  rainy  weather  decreases 
the  vitaHty  of  the  pollen  and  an  excess  of  moisture  often  causes  pollen  grains  to 
swell  and  burst." 

Experimental  evidence  on  the  damaging  influence  of  rain  on  fruit 
setting  is  furnished  by  an  experiment  in  which  a  Mount  Vernon  pear 
tree  was  sprayed  continuously  for  219  hours  while  in  bloom.  ^^  This 
tree  set  very  little  fruit  while  a  tree  of  the  same  variety  standing  nearby 
and  not  subjected  to  such  treatment  set  a  good  crop.  Similar  results 
were  obtained  with  two  Duchess  grape  vines. 

However,  plants  possess  many  protective  devices  which  serve  to 
reduce  injury  to  their  blossoms  from  rain.  Thus  in  Vaccinium  and 
many  other  genera  the  flower  is  pendent  and  the  essential  organs  are 
protected  by  a  bell-shaped  corolla;  in  Opuntia  and  many  others  the 
petals  close  over  stamens  and  stigma  during  damp  weather;  the  male 
racemes  of  the  Juglandacese  and  Cupuliferse  are  pendulous  and  shed 
water  almost  perfectly  when  mature  and  in  Vitis  anthers  that  have 
dehisced  and  shed  part  of  their  pollen  close  and  shut  out  water  upon  the 
advent  of  rain."  In  the  investigation  just  citied,  it  was  found  that 
pollen  of  the  Duchess  grape  when  examined  under  the  microscope 
after  11  days  of  continuous  spraying  was  apparently  uninjured.'*^  Work 
with  the  plum  has  shown  conclusively  that  after  pollination  the  pollen 
is  washed  from  the  stigmas  only  with  great  difficulty  and  that  stigmas 
will  secrete  their  fluid  a  second  time  if  rain  removes  that  first  secreted.  ^^ 
Rain,  however,  is  usually  accompanied  by  temperatm-es  below  those 
characterizing  fair  weather  at  the  same  season.  Thus  Hedrick  in  the 
report  just  cited  states  that  "rainfall  came  in  periods  of  prolonged  cold 
weather  in  the  years  1881,  1882,  1883,  1886,  1888,  1889,  1891,  1892,  1894, 
1898,  1905.  Frosts  and  cold  weather  accompanied  the  rains  in  1888, 1889, 
1890,  1891,  and  1892."  In  the  light  of  these  and  many  other  observa- 
tions and  findings  as  to  the  distinctly  different  effects  of  low  temperature 
on  rate  of  pollen  tube  growth  and  time  of  style  abscission,  it  may  be 
questioned  if  rain  at  blossoming  is  in  itself  a  very  important  factor  in 
limiting  the  set  of  fruit.  Other  conditions,  particularly  lower  tempera- 
tures, with  which  rain  is  generally  associated,  and  interference  with  the 
work  of  pollen-carrying  insects,  are  more  important.     This  statement 


518  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

is  not  made  for  the  purpose  of  minimizing  the  importance  of  "rainy 
weather"  at  blossoming  in  reducing  the  fruit  crop.  It  is  desirable, 
however,  that  there  be  a  correct  understanding  of  the  relative  importance 
of  the  different  factors  that  usually  constitute  "rainy  weather"  and  that 
there  be  a  realization  that  even  a  hard  rain,  if  of  short  duration  and  not 
accompanied  by  very  low  temperatures,  is  not  ordinarily  a  serious  limit- 
ing factor  in  this  connection. 

Wind. — The  average  fruit  grower  regards  wind  as  one  of  the  most 
important  agents  in  the  transfer  of  pollen  from  stamen  to  stigma.  Many 
plants,  such  as  the  walnuts,  oaks,  hickories  and  hazels,  are  wind-polli- 
nated and  with  these  a  reasonable  amount  of  wind  at  blossoming  is  a 
distinct  aid  in  securing  a  good  set  of  fruit.  However,  the  majority  of 
the  deciduous  fruit  crops  are  insect-pollinated.  With  these,  wind  hinders 
rather  than  helps  pollination,  since  bees  and  other  pollen-carrying  insects 
work  most  effectively  in  a  still  atmosphere  and  in  a  strong  wind  they 
refuse  to  work  at  all.  Abundant  evidence  on  this  point  may  be  found 
in  orchards  with  some  exposed  and  some  protected  situations.  Other  con- 
ditions equal,  there  will  be  a  much  better  set  of  fruit  where  the  trees  are 
protected  from  the  full  sweep  of  the  wind  and  in  exposed  places  there  is  often 
a  much  better  set  on  the  leeward  than  on  the  windward  side  of  the  trees. 
In  addition  to  the  indirect  effect  of  wind  through  interfering  with 
the  work  of  pollen-carrjdng  insects,  it  may  operate  more  directly  in  whip- 
ping about  the  flowers  and  causing  mechanical  injuries.  It  may  also  cause 
the  stigmatic  fluid  to  dry  prematurely  and  thus  prevent  the  germination 
of  the  pollen  grains.  In  some  species  at  least,  the  action  of  wind  is  more 
pronounced  early  in  the  usual  period  of  pistil  maturity  than  later. ^^ 

There  are  many  cases  in  which  the  protection  afforded  the  fruit 
plantation  at  the  time  of  blossoming  is  of  greater  importance  than  any 
other  service  rendered  by  a  windbreak. 

Fungous  and  Bacterial  Diseases. — The  flowers  of  many  species  are 
subject  to  the  attacks  of  various  fungous  and  bacterial  diseases  and  often 
their  work  at  this  time  is  serious  enough  greatly  to  reduce  the  set  of 
fruit.  Thus  fire  blight  is  generally  recognized  as  one  of  the  most  impor- 
tant factors  in  limiting  the  set  of  fruit  in  pears;  the  apple  and  the  pear 
scab  are  responsible  for  the  falling  of  many  flowers  of  those  fruits  at  or 
shortly  after  blossoming;  brown  rot  attacks  the  blossoms  of  practically 
all  the  stone  fruits;  black  rot  works  on  grape  blossoms,  causing  many 
to  drop;  the  flowers  of  the  mango^"®  are  attacked  frequently  by  an 
anthracnose;  the  list  might  be  extended  almost  indefinitely.  Naturally 
the  losses  occasioned  by  these  fungous  and  bacterial  attacks  at  the  time 
of  fruit  setting  vary  greatly  with  locality,  variety  and  seasonal  conditions. 
For  instance,  there  are  certain  restricted  areas  where  fire  blight  of  the 
pear  and  apple  is  not  found,  though  the  disease  may  levy  a  very  heavy 
toll  on  pear  blossoms  a  hundred  miles  distant.     The  Grimes  apple  is  but 


UNFRUITFULNESS  ASSOCIATED  WITH  EXTERNAL  FACTORS  519 

little  subject  to  the  scab  fungus  and  ordinarily  its  setting  of  fruit  will  not 
be  materially  reduced  by  it,  though  a  Winesap  crop  in  the  same  orchard 
may  be  practically  ruined  by  its  work  upon  the  blossoms.  In  California 
brown  rot  is  a  serious  disease  on  the  blossoms  of  the  apricot  only  in 
"regions  exposed  to  ocean  influences  and  does  not  develop  except  in 
times  of  unusually  moist  weather.""^ 

Fortunately  most  of  the  fungous  and  bacterial  diseases  that  attack 
the  blossoms  of  fruit  trees  can  be  controlled  by  spraying  or  other  preven- 
tive measures;  consequently  losses  due  to  these  factors  are  avoidable  in 
many  cases. 

Spraying  Trees  When  in  Bloom. — Though  spraying  trees  with  the 
proper  materials  may  be  effective  in  preventing  the  attacks  of  certain 
diseases  that  otherwise  would  seriously  reduce  the  set  of  fruit,  it  is  not 
necessary  or  desirable  to  spray  during  blossoming.  Spray  applications 
at  that  time  are  seldom  recommended  and  are  generally  regarded  as 
undesirable.  They  may  reduce  the  set  of  fruit  either  directly  through 
injuring  the  pollen  or  stigma  or  indirectly  through  interfering  with  the 
work  of  bees  and  other  pollen-carrying  insects. 

Beach*  made  a  number  of  laboratory  cultures  of  pollen  grains  in 
media  to  which  varying  amounts  of  Bordeaux  mixture  alone  and  Bor- 
deaux mixture  with  an  arsenical  poison  had  been  added.  He  found 
that  200  parts  of  Bordeaux  mixture  to  10,000  parts  of  his  culture  media 
practically  prevented  the  germination  of  pollen  and  that  much  smaller 
amounts  had  a  distinct  inhibiting  influence.  On  the  other  hand  in  one 
experiment  sprajdng  apricots  when  in  bloom  with  the  regular  summer 
strength  of  the  lime-sulfur  mixture  and  with  a  weak  Bordeaux  mixture 
caused  no  injury  to  the  flowers  and  no  interference  with  fruit  setting. ^^ 
This  suggests  at  least  that  in  actual  field  practice  no  great  injury  in 
fruit  setting  is  likely  to  result  from  the  use  of  fungicides  alone  when  trees 
are  in  bloom. 

Apparently  the  indirect  effects  on  fruit  setting  of  spraying  with 
arsenical  poisons  when  trees  are  in  bloom  are  much  more  serious.  It 
has  been  shown  that  a  very  small  amount  of  arsenic — less  than  0.0000005 
gram  of  arsenious  trioxide — is  a  fatal  dose  for  a  bee  and  most  bees  die 
within  a  few  hours  after  being  poisoned.  ^"^  Bees  work  as  freely  upon 
sprayed  as  upon  adjacent  unsprayed  trees.  Price ^"^  found  that  the  mor- 
tahty  of  bees  in  a  check  cage  was  only  19  per  cent.,  as  compared  with  69 
per  cent,  in  a  lime-sulfur-arsenate  of  lead  sprayed  cage  and  as  compared 
with  49  per  cent,  in  a  sulfur-arsenate  of  lead  dusted  cage. 

The  suggestion  is  made  that  if  it  has  been  impossible  to  spray  before 
blossoming  for  the  control  of  fungi  which  interfere  with  fruit  setting  and 
such  fungi  are  known  to  be  present  to  a  serious  extent,  spraying  may  con- 
tinue into,  or  even  through,  the  blossoming  season,  but  a  fungicide  alone 
should  be  used  at  that  time. 


520  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Other  Factors  that  Cause  the  Dropping  of  Fruit  and  Flowers. — Many 
other  agencies  besides  those  mentioned  may  occasionally  cause  flowers  or 
developing  fruits  to  drop  prematurely.  Among  these  may  be  mentioned 
the  presence  of  small  amounts  of  illuminating  gas  in  the  atmosphere.^* 

BushnelP^  has  found  that  fruit  setting  in  certain  cucurbitaceous 
plants  is  characterized  by  a  distinct  periodicity.  That  is,  flowers 
opening  during  a  2-  or  3-day  period  may  set  freely,  those  opening 
during  the  next  2  or  3  days  set  poorly,  then  there  is  another  period  of 
good  setting  and  so  on. 

Summary. — The  most  important  of  the  direct  effects  of  the  environ- 
ment through  the  plant  itself  is  in  influencing  nutritive  conditions. 
Soil  type,  water  supply,  fertilizers,  cultivation  and  pruning  are  more 
or  less  important  in  this  connection.  Low  temperature  and  rain  are  the 
two  most  important  of  the  environmental  factors  indirectly  affecting 
fruit  setting  through  affording  or  preventing  the  opportunity  for  pollina- 
tion, the  germination  of  the  pollen  grain  and  fertilization. 

It  is  evident  from  the  subject  matter  presented  in  this  and  the  two 
preceding  chapters  that  the  whole  subject  of  fruit  setting  is  complex. 
In  the  first  place  it  depends  on  a  number  of  internal  factors,  many  of 
which  are  entirely  beyond  any  direct  or  indirect  control.  Secondly, 
blossoming  generally  comes  at  a  season  when  great  fluctuations  in 
temperature,  humidity  and  the  other  features  of  environment  are  likely. 
It  is  therefore  not  surprising  that  the  response  of  the  tree  to  the  combina- 
tion of  all  these  interrelated  factors  and  conditions  varies  from  year 
to  year,  from  orchard  to  orchard  and  even  from  tree  to  tree.  It  is 
fortunate  indeed  for  the  grower  that  the  most  important  of  the  limiting 
factors  to  fruit  setting — both  those  internal  and  those  external  to  the 
plant — are  within  the  grower's  control  by  either  direct  or  indirect  means. 


CHAPTER  XXIX 

FACTORS  MORE  DIRECTLY  CONCERNED    IN   THE    DEVELOP- 
MENT OF  THE  FRUIT 

The  discussion  thus  far  has  been  hmited  mainly  to  a  consideration  of 
the  primary  results  of  fertilization.  From  the  grower's  standpoint,  how- 
ever, the  nature  and  extent  of  its  indirect  effects  are  often  of  equal  or  greater 
importance. 

The  immediate  or  primary  result  of  fertilization  is  the  initiation  of  the 
series  of  changes  in  the  mature  embryo  sac  leading  to  the  development 
of  the  embryo  and  endosperm.  The  changes  subsequently  occurring 
in  the  ovarian  wall  and  oftentimes  in  attached  tissues  result  in  the  setting 
and  development  of  the  fruit.  These  are  the  indirect  or  secondary 
effects  of  fertilization. 

Stunulating  Effects  of  Pollen  on  Ovarian  and  Other  Tissues. — Before 
fertihzation  takes  place,  the  pollen  often  has  an  important  influence  on 
the  development  of  ovarian  and  other  tissues  connected  with  the  fruit. 
This  effect  is  independent  of  the  process  of  fertilization  and  may  be  exer- 
cised though  fertilization  never  occurs.  For  example,  Wcllington^^^ 
secured  fruits  of  the  Seckel  pear  by  applying  to  its  stigmas  pollen  of  the 
Yellow  Transparent  apple,  and  Millardet^^  obtained  fruits  of  certain  va- 
rieties of  the  European  grape  by  employing  pollen  oi  A^npelopsishederacea. 
Presumably  in  neither  case  could  fertilization  occur,  though  the  pollen 
tubes  may  have  entered  the  embryo  sacs.  Tritm-ated  pollen  applied 
to  the  stigmas  of  certain  curcurbits  has  induced  a  partial  development  of 
their  fruits ^°  and  fully  formed  but  seedless  fruits  of  certain  species 
have  been  obtained  by  applying  to  their  stigmas  spores  of  Lycopodium^^ 
In  both  of  these  cases  fruit  development  must  be  attributed  to  the  stimu- 
lating influence  of  the  pollen  or  spores.  Goodspeed''^  reports  that  emas- 
culated but  unpoUinated  flowers  of  the  Thompson  Seedless  grape  do  not 
set  fruit;  however,  emasculated  and  pollinated  flowers  set  freely,  though 
the  resulting  fruits  are  seedless  because  of  embryo  sac  degeneration. 

Some  of  the  most  interesting,  and  perhaps  among  the  most  striking, 
cases  of  response  to  the  stimulus  of  pollination  are  found  among  the 
orchids.^'  In  most  species  of  this  family  the  ovule  is  in  a  very  rudimen- 
tary stage  of  development  at  the  time  of  pollination.  In  some  of  these 
if  pollination  is  not  effected  the  ovules  never  reach  the  stage  at  which 
fertilization  can  take  place,  but  immediately  after  pollination  the  tissues 
of  the  ovule  proceed  to  complete  their  development  and  finally  reach  the 

521 


522  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

stage  for  fertilization.     In  many  cases  several  weeks  between  the  time  of 
pollination  and  fertilization  are  required  for  the  ovules  to  reach  maturity. 

Kusano,^^  who  studied  the  influence  of  pollination  in  stimulating  the  develop- 
ment of  the  ovary  and  fruit  in  Gastrodia,  found  that  many  fruits  would  develop 
in  this  genus  when  no  pollination  occurred.  These  parthenocarpic  fruits  were 
normal  in  appearance,  .though  somewhat  below  the  average  in  size.  Seeds  were 
formed  but  they  were  without  embryos  and  the  number  of  these  imperfectly 
formed  seeds  was  usually  below  that  in  fruits  resulting  from  ordinary  pollination. 
When  Gastrodia  flowers  are  poUinated  with  pollen  of  Bletia,  another  orchid, 
fruits  likewise  developed  but  they  were  much  larger  than  the  parthenocarpic 
fruits  developing  without  pollination,  though  they  too  were  without  embryo- 
containing  seeds  and  presumably  no  fertilization  had  occurred.  Fruits  of  the 
first  category,  that  is,  those  developing  without  the  stimulus  of  pollination,  were 
classed  as  instances  of  vegetative  or  autonomic  parthenocarpy;  those  of  the 
second  class  were  considered  instances  of  stimulative  or  aitionomic  partheno- 
carpy. Commenting  upon  the  results  of  some  of  his  experiments,  Kusano*^ 
remarks:  "As  regards  the  parthenocarpic  development  by  the  foreign  pollen 
two  points  may  be  worthy  of  consideration.  First,  the  size  of  the  resulting 
fruit  may  depend  on  the  intensity  of  the  stimulus.  This  is  evidenced  by  the 
experiment  with  the  Bletia-poUinium;  pollinated  the  day  of  bloom,  the  poUin- 
ium  sends  out  massive  tubes,  leading  the  fruit  to  maximal  growth,  but  the 
delayed  pollination  brings  about  a  feebler  development  of  the  tube,  perhaps 
owing  to  a  certain  modified  condition  of  the  stigma,  and  consequently  smaller 
fruits  result.  Further,  the  poUinia  of  other  orchids  yield  smaller  fruits  than  the 
Bletia-pollinium,  in  conformity  with  the  feeble  development  of  the  pollen-tubes. 
Secondly,  it  may  be  most  probable  that  the  size  of  the  fruit  correlates  with  the 
duration  of  the  stimulus  acted  upon.  The  product  of  the  normal-sized  fruit  by 
crossing  Bletia  appears  to  be  due  to  the  longevity  of  activity  of  the  pollen-tube, 
remaining  alive  and  vigorous  far  beyond  the  period  of  maturation  of  the  fruit, 
and  thus  exerting  the  stimulus  unceasingly  upon  the  ovules  and  ovary  throughout 
the  interval  of  their  complete  development.  ...  As  far  as  observed  in 
Gastrodia,  we  are  led  to  the  view  that  the  ovarial  development  is  correlated 
with  the  embryogenic  development  of  the  ovules  when  the  tube  of  its  own 
pollinium  is  concerned,  but  when  it  is  induced  by  the  foreign  pollen  tube,  it  is 
likely  comparable  to  the  gall  formation  by  the  action  of  fungi  or  insects.  So  that, 
though  the  kind  of  the  stimulus  is  unknown,  whether  chemical  or  mechanical, 
we  may  ascribe  the  resulting  effect  to  an  incessant  stimulus  of  suflScient  intensity." 

The  Effect  of  Certain  Stimulating  Agents  on  Fruit  Setting. — It 
has  long  been  known  that  the  fruits  of  certain  species  which  seldom  or 
never  develop  parthenocarpically  can  be  made  to  set  occasionally  by 
treating  the  stigmas  with  certain  stimulating  agents  other  than  pollen. 
Indeed  the  use  of  Lycopodium  spores,  mentioned  in  a  preceding  paragraph, 
may  be  regarded  as  a  stimulating  agent  of  this  character.  Hartley^^ 
secured  a  partial  set  of  fruit  in  tobacco  by  treating  receptive  stigmas  with 
magnesium  sulfate  and  other  chemicals.  The  seeds  of  these  fruits 
were  poorly  developed  and  without  embryos.  Wellington, ^^'^  working 
with  the  same  species,  obtained  some  fruits,  likewise  without  good  seeds, 


THE  DEVELOPMENT  OF  THE  FRUIT 


523 


by  "singeing  young  buds  with  a  hot  platinum  wire,  by  exposure  of  young 
plants  to  chloroform  gas,  and  by  cutting  away  a  portion  of  the  pistil  and 
pollinating  the  stub  both  with  and  without  the  accompaniment  of  a 
germinative  fluid."  The  ovaries  of  certain  orchids  can  be  made  to 
develop  into  fruits  by  the  mechanical  irritation  of  the  stigmas.  ^^ 

Closely  related  to  the  effects  of  mechanical  irritation  and  of  various 
chemicals  on  fruit  setting  are  those  of  the  presence  or  the  stings  of 
certain  insects.  Miiller-Thurgau"  stated  that  the  presence  of  a  certain 
gall  insect  would  cause  the  setting  of  pear  flowers  and  a  brief  rapid 
growth  of  the  fruit,  though  these  insect-infested  specimens  fell  before 
reaching  maturity.  Figure  54  shows  a  flower  cluster  of  the  LeBrun  pear 
shortly  after  petal  fall.  The  outside  flowers  had  been  pollinated,  had 
set  fruit,  and  were  developing  normally;  of 
the  two  center  specimens  one  had  not  been 
pollinated  and  was  about  to  drop;  the  other, 
infested  with  the  gall  insect,  had  not  only 
set  but  was  enlarging  much  more  rapidly 
than  fruits  developing  normally.  Kraus^^ 
reports  that  no.t  only  fruits  but  embryo- 
containing  seeds  often  develop  from  the 
flower  clusters  of  self  sterile  and  self  barren 
apple  varieties  when  those  flower  clusters 
are  attacked  by  aphids.  The  same  devel- 
opment has  been  recorded  in  the  sweet 
cherry.^"  In  such  instances  the  resulting 
fruits  are  generally  much  dwarfed  and  mal- 
formed and  seldom  can  the  seeds  be  made 
to  germinate;  as  a  rule  the  fruits  contain 
fewer  and  smaller  seeds  than  normally  devel- 
oped specimens  of  the  same  varieties. ^"^ 

Some  observations  of  Johnson"^  on  this  point  are  very  interesting.  Several 
species  of  cacti  often  retain  their  fruits  long  after  maturity.  They  may  persist 
for  months  or  in  some  cases  for  years.  Johnson,  examining  a  large  number  of 
plants  of  Opuntia  versicolor  in  April  and  May,  found  only  about  25  per  cent, 
bearing  persistent  fruits.  However,  about  9  out  of  10  of  those  plants  which  did 
bear  apparently  normal  persistent  fruits  bore  also  abnormal  gall  fruits,  the 
result  of  the  stings  of  one  of  the  gall  insects.  This  led  Johnson  to  suggest, 
"that  the  cause  of  the  persistence  of  the  normal  fruits  may  be  the  same  as  the 
cause  of  the  abnormality  as  well  as  of  the  persistence  of  the  far  more  common 
gall  fruits." 

One  of  the  most  interesting  cases  of  the  influence  of  the  presence 
of  insects,  independent  of  their  pollen-carrying  activities,  on  fruit 
setting  is  found  in  the  male  fig,  or  caprifig.2i)*0;ii2  These  are  not  in 
fact  male  trees;  their  flower  clusters  contain  both  staminate  and  pistillate 


Fig.  54. — Fruit  cluster  of  the 
LeBrun  pear.  The  central  fruit 
has  been  parasitized.  The  outer 
two  have  set  and  are  developing 
normally.  The  other  one  is  about 
to  fall  off.  In  the  cross  section, 
larvse  are  shown  at  g.  {After 
Midler-Thurgau.^'') 


524  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

flowers.  Occasionally  some  of  the  pistillate  flowers  of  these  clusters  are 
pollinated  and  develop  seeds,  but  as  a  rule  if  the  Blastophaga  wasps  enter 
the  cluster  they  oviposit  in  the  pistillate  flowers  and  so-called  gall  flowers 
result.  While  the  larvae  of  the  Blastophaga  are  developing  in  the  gall 
flowers  the  staminate  blossoms  of  the  cluster  mature  so  that  their  pollen 
is  shed  when  the  mature  wasps  are  ready  to  emerge.  Such  flower 
clusters  on  the  caprifig  are  known  as  insectiferous  figs.  If,  however,  the 
Blastophaga  wasps  do  not  enter  these  clusters  at  the  stage  when  their 
pistillate  flowers  are  ready  for  pollination  or  oviposition,  the  cluster 
may  or  may  not  persist  until  its  staminate  flowers  mature  their  pollen. 
(From  a  practical  standpoint  their  remaining  and  maturing  is  of  no 
value,  since  no  wasps  are  in  them  to  emerge  and  carry  pollen  to  the 
flowers  of  pistillate  trees.)  Such  clusters  are  known  as  polliniferous  figs. 
In  any  case  they  drop  off  before  the  insectiferous  figs  reach  full  maturity 
and  the  dropping  is  in  a  way  comparable  to  the  June  drop  of  many  other 
fruits.  Since  pollination  is  unnecessary  for  the  setting  and  persistence 
of  the  insectiferous  fig  it  must  be  concluded  that  the  mechanical  or  chem- 
ical stimulus  resulting  from  the  insect's  presence  is  the  real  cause  of 
setting.  The  growth  stimulus  changes  the  twigs  and  branches^"  bearing 
insectiferous  figs  so  that  they  may  be  told  readily  from  those  bearing 
only  polliniferous  figs  by  their  thickness,  length  and  general  vigorous 
appearance.  This  response,  not  unlike  that  frequently  attending  the 
injection  of  some  chemical  substance  into  vegetative  tissue,  is  at  least 
suggestive  of  the  complexities  involved  in  fruit  setting. 

Seedlessness  and  Parthenocarpy. — Seedless  fruits  are  found  in 
practically  all  fruit-producing  species.  In  some  cases  they  are  of  rather 
infrequent  occurrence,  their  production  apparently  depending  on  unusual 
conditions  of  culture  or  environment.  In  others  they  appear  frequently 
and  many  seedless  strains  or  varieties  have  been  established  and  are 
propagated  extensively  by  vegetative  means.  In  such  cases  the  seed- 
lessness is  due  primarily  to  internal  causes  that  are  usually  but  little 
influenced  by  changes  in  environment. 

Investigations  with  the  grape  by  Stout^^^  have  led  to  this  conclusion:  "The 
most  effective  course  in  breeding  for  the  development  of  seedless  sorts  is  suggested 
by  the  conditions  of  intersexualism.  Most  individuals  and  varieties  producing 
seedless  or  near-seedless  fruits  are  strongly  staminate.  The  former  can  be  used 
as  male  parents  on  the  latter,  which  do  produce  a  few  viable  seeds.  Plants 
strongly  male  and  seedless  can  be  crossed  with  plants  strongly  male  but  weakly 
female  and  near-seedless  and,  also,  the  self-fertilized  progeny  of  the  latter  may 
be  obtained.  In  this  way  families  weak  in  femaleness  may  undoubtedly  be 
obtained  in  which  a  considerable  number  of  individuals  will  produce  seedless 
fruits." 

Parthenocarpy  refers  to  the  ability  of  a  plant  to  develop  its  fruit  (1) 
without  fertilization  or  even  (2)  without  the  stimulus  that  comes  from 


THE  DEVELOPMENT  OF  THE  FRUIT  525 

pollination.  In  other  words,  the  growth  of  the  ovarian  and  other 
tissues  of  the  fruit  can  occur  without  any  stimulus  from  the  accom- 
panying development  of  the  ovules  into  seeds,  Parthenocarpic  fruits  are 
usually,  but  not  always,  seedless.  In  some  species  fruits  will  develop 
and  viable  seeds  will  be  formed  even  if  no  pollination  takes  place.  Such 
plants  are  parthenocarpic  and  parthenogenetic  at  the  same  time.  (Par- 
thenogenesis is  common  in  certain  strawberry  varieties.)  Furthermore, 
many  parthenocarpic  fruits  contain  aborted  or  partly  developed  seeds, 
or  seeds  that,  though  normal  in  appearance,  are  incapable  of  germination. 
On  the  other  hand,  not  all  seedless  fruits  are  parthenocarpic.  In  some 
cases  seedlessness  is  due  to  embryo  abortion  some  time  after  fertilization; 
unless  pollen  had  been  available  to  furnish  the  stimulus  for  fruit  setting 
no  later  development  of  the  fruit  would  have  been  possible. 

It  is  evident  therefore  that  seedlessness  and  parthenocarpy  are 
rather  distinct  phenomena  though  it  frequently  happens  that  the  two 
are  associated. 

Seedlessness  of  N on-'parthenocarpic  Fruits. — The  immediate  cause 
of  seedlessness  in  fruits  that  have  not  developed  parthenocarpically  is 
embryo  abortion.  This  in  turn  may  be  due  either  to  internal  or  to  exter- 
nal factors.  Frost  or  freezing  temperature  after  the  fruit  has  set  is 
perhaps  one  of  the  most  common  of  the  environmental  factors  leading  to 
this  condition;  it  has  been  observed  repeatedly  in  pears,  apples  and 
peaches.  The  developing  embryo  of  the  seed  seems  for  some  reason 
more  tender  to  low  temperatures  than  the  ovarian  and  other  tissues 
surrounding  it.  Consequently  embryo  development  is  arrested;  how- 
ever, if  the  growth  of  the  fruit  has  proceeded  far  enough  it  will  continue 
through  to  maturity,  though  such  fruits  are  often  materially  smaller 
than  those  containing  seeds.  In  many  pear  varieties,  particularly 
those  that  normally  are  either  elongated  or  pyriform,  the  seedless  speci- 
mens are  generally  quite  distinct  in  shape. ^^  Each  has  a  shorter  trans- 
verse diameter  through  the  core,  but  is  much  thickened  at  the  basal  end. 
Sandsten^i^  has  produced  seedless  tomatoes  by  excessive  feeding. 
Though  no  statement  is  made  as  to  whether  or  not  these  fruits  developed 
parthenocarpically,  it  is  presumable  that  pollination  at  least  and  prob- 
ably fertilization  took  place  and  that  seedlessness  was  due  to  embryo 
abortion. 

In  a  preceding  paragraph  it  was  shown  that  full  matm'ity  of  the  fruits 
on  a  caprifig  tree  is  usually  attained  only  when  some  of  its  pistillate 
flowers  are  inhabited  by  the  developing  Blastophaga  wasp.  Ordinarily 
these  fruits  matm-e  no  seeds  because  few  or  none  of  the  pistillate  flowers 
are  pollinated.  In  this  fruit,  then,  embryo  abortion  and  seedlessness  are 
associated  with  a  stimulus  resulting  from  the  attack  of  a  certain  insect. 

Embryo  abortion,  resulting  in  seedlessness,  is  not,  however,  always 
due  to  external  factors.     For  instance,  according  to  one  investigator  only 


526  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

about  25  per  cent,  of  the  fruits  of  the  Blue  Damson  plums  contained  good 
plump  seeds.  ^^  The  remaining  75  per  cent,  were  seedless  or  their  seeds 
were  only  half  grown  and  non-viable.  Many  other  plum  varieties  were 
found  to  bear  a  large  percentage  of  seedless  fruits.  Nevertheless,  none 
of  these  varieties  developed  fruit  parthenocarpically  and  in  some  of  them 
cross  pollination  was  necessary  for  any  set  at  all.  "  The  kind  of  pollen  used 
seems  to  have  had  little  bearing  upon  the  relationship  of  fruit  production 
to  seed  production,  as  the  percentage  of  seeds  developed  in  any  variety 
seems  to  be  rather  constant  regardless  of  the  kind  of  pollen  used."^^ 
The  same  type  of  seedlessness  has  been  observed  in  many  sweet  cherry 
varieties,  in  the  May  Duke  cherry  reaching  sometimes  over  95  per  cent, 
of  the  fruits.  Seedlessness  that  is  not  associated  with  parthenocarpy  is 
likewise  frequent  in  some  of  the  cultivated  varieties  of  the  filbert,  where 
it  is  a  serious  matter  since  seeds  constitute  the  crop.  A  thorough  study 
would  undoubtedly  show  that  seedlessness  is  frequently  associated 
with  embryo  abortion  in  the  developing  seeds  of  many  cultivated  fruits. 
Though  in  many  varieties  if  seed  abortion  takes  place  at  any  stage 
the  fruit  drops  prematurely,  in  many  others  it  can  occur  at  a  late,  and 
still  others  at  an  early,  stage  and  still  the  fruit  will  persist  and  mature 
properly.  Evidently  seedlessness  from  this  cause  depends  on  the 
varying  requirements  of  the  ovarian  tissues  of  different  fruits  for  the 
stimulus  imparted  to  them  by  the  growth  of  the  partly  developed 
seeds  within.  Instances  of  this  kind,  however,  probably  always  follow 
fertilization. 

Vegetative  and  Stimulative  Parthenocarpy. — Distinction  has  been 
made  between  vegetative  or  autonomic  and  stimulative  or  aitionomic 
parthenocarpy.  In  certain  species  parthenocarpic  development  is 
vegetative;  in  other  species  it  is  stimulative;  in  still  others  both  kinds 
occur.  The  cases  of  parthenocarpy  that  have  been  reported  for  a  number 
of  species  have  not  been  studied  carefully  enough  to  make  possible 
their  classification.  Among  the  fruits  reported  as  vegetatively  partheno- 
carpic may  be  mentioned  the  banana,^  many  varieties  of  the  Japanese 
persimmon, ''°'  ^^  certain  mulberries, ^^  certain  peach  varieties, ^^^  the 
medlar,  ^2  i\yQ  papaya,*^^  the  egg  plant,  summer  squash  and  the  English 
cucumber, ^^  a  number  of  varieties  of  the  orange^^*'  and  many  varieties 
of  the  fig.'*''  These  fruits,  or  certain  of  their  varieties,  either  occasionally 
or  regularly  set  and  mature  fruit  without  the  stimulus  even  of  pollination. 
Among  those  that  have  been  reported  parthenocarpic  when  subjected  to 
certain  stimuli,  usually  the  stimulus  of  pollination,  are  the  pepino,'*^ 
tobacco, *^^  pear^^^  and  Jerusalem  cherry.  ^^^  Many  varieties  of  Musca- 
dine^^" and  of  Labrusca  and  Labrusca-hybrid  grapes^  have  been  reported 
as  occasionally  or  sparingly  parthenocarpic  when  subjected  to  the  stimu- 
lus of  pollination  with  impotent  pollen,  and  the  Thompson  Seedless^^  grape 
is  regularly  parthenocarpic  under  similiar  conditions. 


THE  DEVELOPMENT  OF  THE  FRUIT 


527 


In  discussing  the  influence  of  nutritive  conditions  within  the  plant 
on  fruit  setting  attention  has  been  directed  to  their  influence  on 
parthenocarpy.  Apparently  unusual  accumulation  of  elaborated  foods 
in  proximity  to  flowers  in  the  receptive  stage  often  acts  as  a  stimulus  to 
further  growth  and  development  and  in  this  way  inhibits  the  formation 
of  an  abscission  layer  much  as  would  the  stimulus  occasioned  by  the 
stings  of  certain  insects  or  by  developing  seeds. 

Relation  of  Anatomical  Structure  of  Fruit  to  Parthenocarpy. — As 
has  been  pointed  out,  seedlessness  is  to  be  expected  at  least  occasionally 
in  almost  every  species  and  variety  and  it  is  probable  that  the  same  may 
be  said  of  parthenocarpy.  It  may  be  noted,  however,  that  it  is  more 
frequent  in  species  whose  fruits  the  botanist  classifies  as  inferior,  those 
into  whose  structure  tissues  other  than  the  ovary  enter.  Though  this 
may  be  a  mere  coincidence,  it  at  least  suggests  that  the  greater  stem-like 
character  of  such  fruits  imparts  to  them  a  stronger  tendency  to  persist 


Fig.  55. 


-Developing  fruits  of  the  LeBrun  pear;  a  and  d  normal  seed-containing 
fruits;  b,  c,  e  and  /  seedless.      (After  Muller-Thurgau.^'') 


than  there  is  in  those  whose  tissues  when  mature  are  entirely  carpellary 
in  nature.  They  seem  to  be  less  in  need  of  the  stimulus  of  fertilization. 
In  Fig.  55  are  shown  pears  of  the  LeBrun  variety,  one  of  which  is  develop- 
ing as  a  result  of  the  stimulus  afforded  by  pollination  and  fertilization. 
The  other  two  are  developing  parthenocarpically.  The  greater  develop- 
ment of  the  stem  tissues  in  the  latter  case  is  very  suggestive. 

Suggestive  also  in  this  connection  are  the  following  statements  by  Johnson^* 
on  the  perennation  and  proliferation  of  the  fruits  of  Opuntia  fulgida.  "It  is 
true  that  the  vegetative  joints  and  both  the  fertile  and  sterile  fruits  resemble 
each  other  greatly  in  their  capacity  for  proliferation.  There  seems  no  adequate 
reason,  however,  for  assuming  that  either  the  proUferating  habit  or  the  fimda- 
mental  structure  of  the  fruit  is  a  secondary  thing  in  the  evolution  of  the  opuntias. 
On  the  contrary,  it  is  natural  that  the  thick-skinned,  water-stored  joints  of 
these  cacti  should  have  proved  capable  of  persisting  on  moderately  moist  soil 
until  rooted  deeply  enough  to  secure  a  water-supply  adequate  for  the  starting 
of  a  young  plant.     The  fruit  being   .    .    .   really  a  stem  in  organization,  up  to 


528  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

the  latest  phase  of  its  development,  it  is  also  very  naturally  capable  of  prolifera- 
tion to  root  and  shoot.  The  capacity  of  joint  and  fruit  for  persistence  and  pro- 
liferation is  probably  as  old  as  the  fleshy  character  of  the  family.  The  persistence 
of  the  sterile  fruits,  at  least  to  maturity,  is  not  a  really  surprising  thing,  in  view 
of  the  preponderatingly  vegetative  and  stem-like  character  of  the  bulk  of  the 
wall  of  the  ovary.  Sterile  ovaries  occur  in  many  species  of  angiosperms,  but  in 
most  of  these  the  carpels  constitute  the  bulk  of  the  fruit.  Therefore,  when  the 
seeds  are  wanting  in  these  forms,  and  the  carpels  as  usual  fail  to  develop,  no 
fruit  is  formed  and  the  flower  bud  soon  withers  and  drops  off.  In  Opuntia,  on 
the  contrary,  even  if  the  seeds  and  carpellary  portion  of  the  fruit  do  fail  to  develop, 
the  basal  stem-like  part  may  go  on,  practically  unhindered  in  its  vegetative 
growth,  and  mature  quite  normally." 

Between  the  conditions  represented  by  autonomic  parthenocarpy 
on  the  one  hand  and  varietal  interunfruitfulness  on  the  other  there  is  a 
series  exhibiting  practically  all  possible  expressions  of  the  tendency  to  set 
and  mature  fruit.  Only  a  little  less  extreme  than  the  tendency  to  fruit- 
fulness  shown  by  plants  vegetatively  parthenocarpic  is  that  of  plants 
aitionomically  parthenocarpic.  Next  in  the  series  are  the  plants  that 
can  set  and  mature  fruit  if  self  pollinated  and  fertilized,  though  embryo 
abortion  takes  place  almost  at  once.  These  in  turn  are  followed  by 
plants  which  require  varying  degrees  of  development  in  the  seeds  that 
they  may  properly  mature  their  fruit.  Finally  there  are  those  that 
require  the  maturing  of  viable  seeds  along  with  the  developement  of  their 
fruits  else  premature  dropping  will  occur. 

The  Value  of  Seedless  and  Parthenocarpic  Fruits. — Seedlessness  in 
edible  fruits  is  generally  regarded  as  a  valuable  variety  characteristic 
for  commercial  purposes.  In  many  cases  at  least  the  market  is  willing  to 
pay  a  premium  for  it.  Mention  of  the  regard  in  which  seedless  grapes  and 
oranges  are  held  is  ample  evidence.  Bananas  and  pineapples  containing 
seeds  would  probably  find  a  very  limited  market.  Even  a  material 
reduction  in  the  number  of  seeds  would  be  a  great  asset  in  the  blueberry, 
the  blackberry,  the  watermelon,  the  sugar  apple  and  in  many  other 
fruits.  On  the  other  hand,  in  many  fruits  seedlessness  would  not  be  an 
asset.  There  would  be  little  advantage  in  seedless  apples  or  pears,  if  the 
carpels  remained.  It  has  been  pointed  out  that  many  fruits  of  our 
ordinary  plum  and  cherry  varieties  are  seedless,  but  this  condition  is  not 
generally  known  or  even  suspected  because  the  bony  endocarp  (stone) 
remains  unchanged. 

For  the  grower,  parthenocarpy  probably  is  a  more  valuable  variety 
characteristic  than  seedlessness.  If  his  fruits  are  parthenocarpic  he  is 
insured  against  crop  failure  from  self  and  cross  unfruitfulness  and,  if 
their  parthenocarpy  is  autonomic,  through  failures  resulting  from  lack 
of  pollinating  agents  or  pollinating  weather,  his  setting  of  fruit  is  more  or 
less  guaranteed.  It  should  not  be  inferred,  however,  that  all  the  flowers 
of  parthenocarpic  varieties  set  fruit  and  that  aU  these  fruits  mature. 


THE  DEVELOPMENT  OF  THE  FRUIT  529 

Mention  has  been  made  of  the  relation  of  water  deficiencies  at  blossoming 
or  shortly  thereafter  to  dropping  in  the  Washington  Navel  orange.'* 
]\Iany  other  agencies  that  Hmit  fruit  setting  in  non-parthenocarpic 
varieties  cause  the  dropping  of  those  varieties  that  develop  partheno- 
carpically.  In  other  words,  the  parthenocarpic  condition  is  only  a  partial 
and  not  a  complete  insurance  against  crop  failure  from  premature 
dropping. 

From  a  practical  standpoint  seedlessness  and  parthenocarpy  are  to  be 
considered  more  as  varietal  characteristics  to  be  sought  when  breeding 
or  originating  new  varieties  or  strains,  rather  than  as  conditions  to  be 
produced  by  cultural  means. 

The  Relation  of  Seed  Formation  to  Fruit  Development. — It  has  just 
been  pointed  out  that  in  some  species  or  varieties  ovarian  and  other 
tissues  of  the  fruit  may  develop  independently  of  those  of  the  enclosed 
ovules.  This  condition,  however,  is  by  no  means  universal  and  such 
parthenocarpic  fruits  are  usually  somewhat  different  in  size,  shape  or 
other  characteristics  frcm  seed-containing  specimens  of  the  same  kinds. 
Furthermore,  in  the  seed-containing  specimens  important  differences  in 
development  are  often  associated  with  varying  seed  number  and 
distribution. 

Structure  of  Fruit. — Evidence  that  certain  tissues  of  the  pear  undergo 
a  proportionally  greater  development  in  seedless  than  in  seed-containing 
specimens  is  presented  in  Fig.  55.  That  this  is  very  common  in  other 
fruits  is  indicated  by  the  work  of  many  investigators.  Thus  in  seedless 
eggplants  the  outer  portions  of  the  fruit  grow  more  rapidly  than  the  inner 
portions,  "the  placentae  evidently  requiring  the  stimulus  of  the  growing 
ovules  to  induce  development."^^  In  seedless  fruits  of  the  eggplant  and 
in  those  in  which  the  development  of  the  ovary  is  arrested  at  an  early 
stage  there  is  sometimes  a  very  marked  and  abnormal  development  of 
the  subtending  calyx.  "Usually  the  most  prominent  indication  that 
impregnation  has  taken  place,  in  the  eggplant,  is  the  rapid  growth 
of  the  calyx.  Many  times,  however,  the  calyx  becomes  much  enlarged 
while  for  some  reason  the  ovary  fails  to  develop.  I  have  frequently 
seen  examples  of  this,  in  which  the  calyx  was  fully  6  inches  long."** 
Ewerf*2  studied  the  structure  of  seedless  and  seed-bearing  gooseberry 
fruits  and  found  striking  differences  in  their  cell  size  and  structure.  The 
cells  of  the  placentae  and  inner  ovarian  wall  of  seed-containing  fruits 
averaged  45-90/i^  in  diameter,  while  many  of  those  in  the  seedless  speci- 
mens were  seven  or  eight  times  as  large. 

Form. — The  pears  sho^vn  in  Fig.  55  are  illustrations  of  changes  in  form 
accompanjdng  changes  in  internal  structure  due  to  seedlessness.  Mun- 
son*^  observed  that  the  parthenocarpic  seedless  fruits  of  English  cucum- 
bers were  cylindrical  in  shape,  but  that  when  they  were  pollinated  and 
seeds  developed  the  apical  one-third  of  each  fruit  was  much  enlarged. 


530 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


owing  to  the  location  of  the  seeds  in  that  end  and  not  in  the  basal  portion. 
Seedless  or  nearly  seedless  specimens  of  Taber  No.  129,  a  variety  of 
Japanese  persimmon,  are  almost  conical  and  distinctly  pointed,  while 
seed-bearing  specimens  of  the  same  variety  are  oblate.  Furthermore, 
"Taber  No.  23  when  seedy  is  oblate-rounded,  but  when  seedless  it 
assumes  an  almost  quadrangular  form  with  very  blunt  or  rounded  corners. 
Zengi  is  oblate-rounded  when  seedy,  but  approximates  a  truncated  cone 
in  shape,  or  is  distinctly  oblong  when  seedless. "^*^ 

Size. — Perhaps  an  even  more  striking  influence  of  seed  formation 
on  the  development  of  the  fruit  is  in  size.  Seedless  grapes  are  much 
smaller  than  seed-containing  berries  of  the  same  variety  and  berries 
containing  aborted  seeds  are  intermediate  between  those  that  are  seed- 
containing  and  those  that  are  seedless.*  Seed- containing  gooseberries 
have  been  found  to  average  5  grams  in  weight,  while  seedless  berries  of 
the  same  variety  averaged  only  3  grams,  ^^  Seedless  apples  and  pears 
are  often,  though  not  always,  smaller  than  seed-containing  specimens. 
In  the  date  palm  the  seedless  fruits  maturing  from  unpollinated  flowers 
are  only  one-third  to  half  the  size  of  normal  seed-containing  fruits  of  the 
same  varieties.'"^ 

Furthermore  in  fruits  normally  containing  a  number  of  seeds  consid- 
erable correlation  is  likely  between  the  size  of  the  fruit  and  the  number  of 
seeds  developing.  Munson^^  found  this  true  in  the  tomato  and  he 
observed  that  the  locules  were  well  developed  only  on  the  side  of  the  fruit 
containing  a  considerable  number  of  good  seed.     The  influence  of  seed 


Table  5. — Number  of  Seeds  in  Fruits  That  Drop  and  in  Fruits  That  Remain 

(on  the  Apple  Tree) 

(After  Heinicke^^) 


Number  of 

Baldwin 

Rhode  Island 

Maiden  Blush 

seeds  to 
the  fruit 

Attached 
fruit 

Drop 
fruit 

Attached 
fruit 

Drop 

fruit 

Attached 
fruit 

Drop 
fruit 

1 

2 

6 

1 

3 

2 

5 

16 

13 

4 

17 

3 

9 

12 

4 

18 

9 

17 

4 

9 

7 

1 

9 

7 

8 

5 

14 

4 

5 

15 

4 

6 

6 

6 

6 

5 

2 

10 

7 

7 

3 

5 

1 

10 

3 

8 

1 

1 

6 

2 

11 

4 

9 

1 

6 

10 

1 

2 

11 

1 

12 

1 

13 

1 

THE  DEVELOPMENT  OF  THE  FRUIT 


531 


number  on  the  premature  dropping  of  apples  is  shown  by  data  summarized 
in  Table  5.  Though  the  possession  of  a  certain  number  of  developing 
seeds  did  not  insure  the  fruit  against  dropping  and  though  some  of  the 
few-seeded  fruits  persisted  and  matured,  there  was  a  well-marked  tend- 
ency for  the  latter  to  fall  prematurely  and  an  equally  distinct  tendency 
for  the  several-seeded  fruits  to  persist.  In  a  previous  paragraph  it  was 
pointed  out  that  the  setting  and  maturing  of  apples  is  favored  by  the  size, 
strength  and  vigor  of  the  limbs  and  spurs  on  which  they  are  borne.  Table 
6  presents  further  data  which  show  the  varying  seed  numbers  in  fruits 
of  approximatel}^  the  same  size  but  borne  on  spurs  of  varying  weights. 
It  is  noticeable  that  with  fruit  weights  remaining  constant  the  number 
of  seeds  they  contain  varies  inversely  as  the  weights  of  the  spurs.  In 
other  words,  the  poorer  development  of  fruit  generally  found  on  weak 
spurs  is  offset  if  the  fruits  have  enough  seeds.  This  has  led  to  the  sugges- 
tion that  developing  seeds  have  a  pulling  power  for  water  and  sap, 
enabling  the  fruits  of  which  they  form  a  part  to  develop  more  or  less  at 
the  expense  of  other  fruits  with  presumably  smaller  food-attracting 
abilities. ^^ 


Table  6. — Seed  Number  Compensating  for  Spur  Weight  in  the  Apple 

{After  Heinicke^^) 

(Weight  of  fruit  constant,  number  of  seeds  and  weight  of  spurs  varying) 


Lot 


Variety 


Fruit 
weight 
(grams) 


Number 
of  seeds 
per  fruit 


Spur 
weight 
(grams) 


Tompkins  King 

Tompkins  King 
Tompkins  King 
Tompkins  King 
Rhode  Island.  .  . 
Westfield 


5.54 
5.05 
2.31 
1.98 
3.97 
1.45 
6.09 
3.75 
5.05 
2.40 
4.86 
2.28 
2.33 
1.31 


Experimental  evidence  in  corroboration  of  this  suggestion  was  obtained 
by  coating  with  vaseline  partly  grown  apples  on  spurs  removed  from  trees 
and  exposed  to  a  drying  atmosphere.  It  was  found  that  the  leaves  on  the  spurs 
were  able  to  withdraw  less  water  from  many-seeded  than  from  few-seeded  fruits 
and  more  from  the  side  of  a  fruit  having  no  seeds  than  from  the  side  where  the 
locules  contamed  a  number.*^ 


532 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Muller-Thurgau"  found  a  similar  correlation  between  fruit  size 
and  number  of  seeds  in  grapes,  as  is  shown  in  Table  7,  and  Valleau^^^ 
found  the  size  of  strawberry  fruits  closely  correlated  with  the  number 
of  their  akenes. 


Table  7. — Relation  of  Seed  Number  to  Fruit  Size  in  Grapes 

{After  Mailer-  Th  urgau « ^) 


Seedless 

1  seed 

2  seeds 

3  seeds 

4  seeds 

Variety 

Flesh, 
grams 

Flesh, 
grams 

Seeds, 
grams 

Flesh, 
grams 

Seeds, 
grams 

Flesh, 
grams 

Seeds, 
grams 

Flesh, 
grams 

Seeds, 
grams 

Riesling 

Early  Burgundy 

25.0 
27.9 
23.7 
58.7 
60  3 

58.2 
52.9 
81.6 
135.8 
112  6 

2.1 
1.8 
2.14 
2.4 
3   1 

77.2 
92.4 
116.7 
196.6 
202.0 

3.9 

3.7 

4.12 

5.0 

7.4 

89.0 
110.5 
140.8 
232.7 
244.4 

5.2 
5.2 
5.9 
7.4 
10.9 

112.0 
140.0 
155.8 

258.8 

6.0 
7.3 

White  Gutedel 

Orleans 

14   9 

It  should  not  be  inferred,  however,  that  seedless  fruits  are  always 
smaller  than  seed-containing  fruits  of  the  same  varieties  or  that  fruits 
containing  many  seeds  are  larger  than  those  containing  but  few.  For 
instance,  in  his  pollination  work  with  plums,  MarshalP^  found  that 
many  varieties  mature  a  large  precentage  of  seedless  fruits.  These 
cannot  be  distinguished  from  those  containing  seeds  by  their  size  or  any 
other  external  characteristic.  The  same  is  true  of  fruits  of  the  sweet 
cherry.  Furthermore  it  has  been  found  that  seed-bearing  fruits  of  the 
Japanese  persimmon  are  uniformly  smaller  than  seedless  specimens 
of  the  same  varieties.'''' 

Composition  and  Quality. — Associated  usually  with  differences  in 
the  structure  of  fruits  are  variations  in  composition  and  quality.  This 
holds  true  for  the  structural  changes  associated  with  varying  seed  number, 
and  indeed  the  differences  in  composition  are  often  greater  than  would 
be  expected  from  observation  of  the  variations  in  structure.  Table  8 
shows  the  sugar  content  and  acidity  of  seedless  and  normal  pears  and 
Table  9  shows  differences  in  composition  between  caprified  and  un- 
caprified  figs  of  several  varieties.  The  difference  in  acidity  between 
the  seedless  and  seed-containing  pears  is  striking  and  is  sufficient  to 
make  a  considerable  variation  in  quality.  Though  the  distinctions 
between  the  caprified  and  the  uncaprified  figs  are  on  the  whole  less 
prominent  they  are  great  enough  to  be  of  commercial  importance  in 
such  varieties  as  the  Dottato.  There  are  differences  also  in  color  of 
flesh   between   caprified   and   uncaprified   figs   of   the   same   variety.  ^^^ 

Perhaps  the  most  striking  dissimilarities  in  composition  and  quality 
between  seedless  and  seed-bearing  fruits  are  found  in  certain  varieties 
of  the  kaki  or  Japanese  persimmon.  Zengi,  Hyakume  and  certain  other- 
sorts  are  always  solid,  dark  fleshed  when  they  have  a  good  supply  of 


THE  DEVELOPMENT  OF  THE  FRUIT 


533 


Table   8. — Influence   of   Seed    Number   on   Sugar  Content  and  Acidity  in 

Pears 

{After  Ewert'-) 


Grams  of  reducing  sugar  in  100 
cubic  centimeters  of  sap 


Grams  of  acid,  calculated  as  malic 

acid,  in  1000  cubic  centimeters  of 

sap 


Fruits  seedless j 

Fruits  1-seeded I 

Frui.ts  2-seeded .• .  . 


5.81 
8,33 
9.26 


0.98 
1.61 
1.79 


Table  9. — Analyses  of  Caprified  and  Uncaprified  Figs 
(After  CoruUr-^) 


Variety  I      Analysis  by 

I 

Fig   d'Or,  caprified Du  Sablon 

Fig  d'Or,  uncaprified j  Du  Sablon 

Fig   Datte,  caprified |  Du  Sablon 

Fig   Datte,  uncaprified j  Du  Sablon 

Bourjassotte,  caprified Du  Sablon 

Bourjassotte,  uncaprified j  Du  Sablon 

Adriatic,  caprified W.  V.  Cruess 

Adriatic,  uncaprified W.  V.  Cruess 

Dottato,  caprified  (Kadota) W.  V.  Cruess 

Dottato,  uncaprified  (Kadota) W.  V.  Cruess 

Dottato  (dried),  caprified F.  W.  Albro 

Dottato  (dried),  uncaprified F.  W.  Albro 

Adriatic  (half  dried),  caprified    F.  E.  Twinning 

Adriatic  (half  dried),  uncaprified F.  E.  Twinning 

Adriatic  (fresh),  uncaprified M.  E.  Jaffa 

Adriatic  (fresh),  caprified M.  E.  Jaffa 

Adriatic  (dry),  uncaprified M.  E.  Jaffa 

Adriatic  (dry),  caprified '  M.  E.  Jaffa 


Per  cent 

Per  cent 

water 

sugar 

80.00 

11.20 

74.00 

12.60 

71.00 

14.30 

71.00 

18.70 

70.00 

3.50 

76.00 

6.20 

19.05 

18.00 

35.20 

28,40 

22.57 

75.36 

25.75 

68.16 

27.05 

34.80 

28.70 

35.50 

70.70 

18.78 

74.70 

13.00 

18.00 

51.50 

16.00 

48.50 

seeds,  or  when  there  are  only  three  or  four  seeds  and  these  are  well 
distributed.'"  When  there  is  only  a  single  seed,  or  two  or  three  seeds 
in  adjacent  locules,  the  flesh  surrounding  these  is  dark  while  that  some 
distance  away  is  light  colored.  When  these  varieties  produce  seedless 
fruits  all  of  their  flesh  is  hght  colored.  O'kame  and  Yemon,  possessing 
full  complements  of  seeds,  have  dark  colored  flesh  immediately  surround- 
ing the  seeds,  but  light  colored  flesh  next  to  the  skin.  Tsuru,  Costata, 
Triumph  and  some  others  are  light  fleshed  whether  seeds  are  present 
or  not.  The  dark  flesh  of  persimmons  is  edible  while  stiU  hard  and  flrm, 
but  the  light  flesh  remains  astringent  untfl  it  softens.  Hume'"  states 
that  no  variety  is  known  which  is  dark  fleshed  when  seedless,  but  Condit^" 
reports  an  apparent  exception  to  this  rule. 

Variation  in  seed  number  is  accompanied  by  differences  in  composi- 


534  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

tion  in  many  other  fruits.  In  most  grape  varieties,  for  instance,  seedless 
fruits  are  much  sweeter  than  seed-containing  berries  of  the  same  kinds. 
On  the  other  hand,  the  differences  in  composition  are  often  negligible. 
There  is  no  general  rule  that  can  be  laid  down  stating  that  seedlessness 
tends  either  to  improve  or  to  detract  from  quality. 

Seaso7i  of  Maturity. — There  is  often  a  considerable  difference  in  the 
time  intervals  between  fruit  setting  and  maturing  of  seedless  and  seed- 
containing  fruits  of  the  same  variety.  As  a  rule  the  parthenocarpic  or 
seedless  fruits  are  slower  in  reaching  maturity  than  the  seed-bearing 
specimens.  Munson^^  mentions  several  instances  in  which  flowers  of  the 
cucumber,  pumpkin  and  summer  squash  were  induced  to  set  fruit  by 
applying  to  their  stigmas  pollen  of  certain  other  species  of  cucurbits.  The 
resulting  fruits  which  were  seedless  required  over  2  months  longer  for 
maturity  in  some  cases  and  in  all  cases  a  somewhat  longer  period  than  was 
necessary  for  the  development  of  normal  fruits  from  intra-specific  polli- 
nation. The  so-called  "second  bloom"  fruits  of  the  apple  and  pear  that 
set  2  to  4  weeks  after  the  usual  blossoming  period  and  are  very  often 
seedless  frequently  never  mature  properly  and  such  maturity  as  they  do 
attain  is  reached  only  after  they  have  persisted  on  the  trees  much  longer 
than  the  extra  2  to  4  weeks  that  would  compensate  for  their  late  setting. 
Caprified  figs  of  the  Smyrna  type  drop  from  the  trees  at  full  maturity; 
uncaprified  figs  tend  to  persist  and  usually  must  be  cut  or  pulled  from  the 
trees,  as  they  will  fall  only  when  past  their  prime. '**^  In  the  Japanese 
persimmon  seed-containing  fruits  usually  ripen  earlier.  Zengi  commonly 
matures  its  seed-bearing  fruits  in  late  July,  while  its  seedless  fruits  may 
not  be  ready  for  harvest  untilDecember.^"  In  other  varieties  there  may 
be  less  difference  in  ripening  periods,  though  they  are  often  quite  distinct. 
Fruits  bearing  only  one  or  two  seeds  show  a  tendency  to  ripen  with  the 
seedless,  while  those  with  a  greater  number  show  a  tendency  to  ripen  with 
the  normal  fruits. '''' 

In  almost  all  cases  the  relation  of  seed  number  to  season  of  maturity 
is  of  very  secondary  importance. 

Specific  Influence  of  Pollen  on  Resulting  Fruit.- — Much  has  been 
said  on  the  supposed  specific  influence  of  the  pollen  on  the  characteristics 
of  the  fruit  resulting  from  the  pollination.  For  instance,  it  has  been 
claimed  that  the  red  color  of  striped  apple  varieties  is  intensified  after 
pollenizing  with  a  dark  red  sort.  The  pollination  of  varieties  with 
an  acid  flesh  with  pollen  from  a  sweet  or  subacid  variety  has  been  said  to 
result  in  fruit  less  acid  in  character.  Early  maturing  sorts  are  claimed 
to  mature  their  fruits  somewhat  later  if  pollinated  by  late  ripening  kinds. 
These  conceptions  are  based  on  a  misunderstanding  of  the  processes 
actually  involved  in  pollination,  fertilization  and  fruit  development,  or 
on  faulty  observations,  or  on  a  wrong  interpretation  of  field  observations 
that  may  have  been  accurate. 


THE  DEVELOPMENT  OF  THE  FRUIT 


535 


There  is  no  evidence  to  indicate  any  immediate  influence  of  pollen 
on  the  color  of  the  resulting  fruit,  or  any  direct  effect  on  its  composition, 
flavor,  quality,  shape,  season  of  maturity  or  keeping  quality.  This 
statement  is  borne  out  by  a  number  of  extensive  cross  and  self  pollination 
experiments^^' ^^^  as  well  as  by  a  theoretical  consideration  of  the  nature 
of  the  tissues  and  processes  involved  in  fruit  setting  and  maturing.  Of 
course  if  in  a  series  of  pollination  experiments  some  pollen  is  used  on  a 
certain  variety  and  normal  seed-containing  fruits  result  and  then  pollen 
of  some  other  kind  is  used  on  other  flowers  stimulating  them  to  set  and 
mature  seedless  fruit,  differences  in  size,  shape,  composition  and  season  of 
maturity  may  be  obtained.  However,  these  are  diversities  associated 
more  directly  with  the  relationship  existing  between  seed  formation  and 
fruit  development  and  not  directly  between  kind  of  pollen  and  fruit 
development.  In  the  same  way  the  pollination  of  pistils  of  a  given 
sort  with  pollen  of  half  a  dozen  other  varieties  with  which  it  is  inter- 
fruitful  may  result  in  one  crossing  in  fruits  averaging  say  two  seeds,  in 
another  crossing  in  fruits  averaging  four  seeds,  and  so  on.  Under  these 
conditions  minor  differences  in  size,  composition,  shape  and  even  flesh 
color  and  season  of  maturity  may  follow.  Differences  of  this  kind 
probably  account  for  such  inequalities  in  fruit  size  in  the  pear  as  were 
found  by  Waite^^^  when  he  used  pollen  of  several  kinds  on  Bartlett  or 
Kieffer  pistils  (see  Table  10). 

Table   10. — Influence   of  Kind   of  Pollen   on  Fruit  Size  and  Seed  Weight 

IN  Pears 
{After  Waite  "2) 


Cross 

Average  weight 
of  fruit,  grams 

Average  weight 
of  seeds,  grams 

Bartlett  X  Bartlett 

100.4 
116.1 
167.7 
133.6 
89.4 
114  2 

0  07 

Bartlett  X  Anjou 

0.38 

Bartlett  X  Easter 

0  38 

Bartlett  X  Angouleme. 

Bartlett  X  White  Dovenne 

0.30 
0  27 

Bartlett  X  Clapp  Favorite 

0.32 

The  limited  data  available  indicate  that  these  variations  are  relatively 
unimportant  except  in  comparing  cross  pollinations  with  self  pollinations. 
That  is  to  say,  many  varieties  that  will  set  and  mature  fruit  when  self 
pollinated  will  set  and  mature  distinctly  larger  fruits  when  cross  pollinated, 
regardless  of  the  kind  of  pollen  used  if  only  it  is  from  a  compatible  variety. 
The  explanation  of  the  smaller  fruits  resulting  from  self  pollination 
is  that  though  selfing  often  results  in  fruitf  ulness  the  fruits  bear  few  or  no 
perfect  seeds,  while  the  cross  pollinated  fruits  have  the  usual  number  of 


536  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

good  seeds.  In  other  words,  it  is  crossing  so  as  to  secure  a  good  comple- 
ment of  seeds,  rather  than  crossing  with  some  particular  variety,  that  is 
responsible  for  the  difference  in  size  and  is  consequently  important  in  the 
orchard.  Investigations  conducted  with  many  fruits  indicate  that  the 
number  or  percentage  of  seeds  developing  in  the  fruits  of  different  kinds 
is  to  a  considerable  extent  a  varietal  characteristic  or  at  least  it  is 
more  dependent  on  the  variety  and  the  condition  of  the  tree  or  plant 
than  on  the  kind  of  pollen,  assuming  that  an  adequate  supply  of  good 
pollen  is  available. 

Kraus^^  has  pointed  out  that  the  occasional  striping  of  self  colored 
fruits  of  the  apple,  so  often  cited  as  proof  of  an  immediate  influence  of  the 
pollen  on  the  character  of  the  resulting  fruit,  is  in  reality  a  special  form  of 
bud  mutation.  Bud  mutations  of  this  kind  may  in  many  cases  be  propa- 
gated vegetatively  and  striped  varieties  obtained. 

What  appears  at  first  as  an  exception  to  some  of  the  preceding  statements 
has  been  recorded  for  the  developing  fruits  of  the  vanilla.  McClelland'^  crossed 
two  types  of  this  plant — Vanilla  planifolia  and  the  "vanillon"  type.  "The 
typical  well-developed  fruit  of  V.  planifolia  from  a  close-fertilized  blossom  is  a 
long  slender  capsule  tapering  at  the  stem  end  but  carrjdng  its  fullness  well  down 
toward  the  blossom  end.  It  contains  thousands  of  tiny,  oily,  black  seeds. 
.  .  .  The  fruits  [of  the  vanillon  type]  are  much  thicker  and  shorter  .  .  . 
and  differ  in  being  of  a  more  uniform  thickness  near  the  two  ends,  the  blossom 
end  frequently  being  rather  tapering.  Where  to  either  the  V.  planifolia  or  the 
vaniUon  stigma  pollen  of  the  other  has  been  applied  a  very  marked  modification  in 
the  form  of  the  fruit  has  resulted."  These  differences  in  shape  apparently  are 
associated  with  the  location  within  the  capsule  of  the  ovules  that  were  fertilized 
and  develop  into  seeds.  When  V.  pla^iifolia  pollen  is  used  on  vanillon 
stigmas,  fertilization  takes  place  mainly  toward  the  apical  end  of  the  ovary  and 
not  toward  the  basal  end,  while  in  self  pollenized  vanillon  stigmas  fertiliza- 
tion occurs  clear  to  the  bottom  of  the  ovarian  cavity.  On  the  other  hand,  the 
pollen  tubes  of  the  vanillon  type  seek  the  basal  ovules  in  the  ovaries  of  the 
V.  planifolia  type  when  that  crossing  is  made.  In  reality,  instead  of  being  an 
exception  to  the  statement  that  crossing  with  a  particular  kind  of  pollen  affords 
no  direct  influence  on  the  character  of  the  resulting  fruit,  this  is  but  another 
instance  of  an  indirect  effect  on  shape,  the  direct  relationship  being  between 
kind  of  pollen  and  seed  number  in  the  one  case  and  seed  number  and  location 
and  shape  of  fruit  in  the  other. 

Summary. — Ordinarily  the  development  of  the  carpellary  and  other 
tissues  of  the  fruit  depends  on  fertilization  and  the  consequent  develop- 
ment of  seeds  from  the  ovules.  In  some  cases,  however,  the  development 
of  the  fruit  may  proceed  without  an  accompanying  growth  of  seeds,  or 
even  without  the  stimulus  of  fertilization.  In  still  other  cases  develop- 
ment may  occur  in  the  absen.ce  of  pollination.  Parthenocarpy  is  a  term 
used  to  cove-r  those  cases  of  f-ruit  development  in  the  absence  of  fertiliza- 


THE  DEVELOPMENT  OF  THE  FRUIT  537 

tion.  Parthenocarpic  fruits  are  usually  seedless,  though  seeds  may  de- 
velop in  them  parthenogenetically.  Some  seedlessness  is  due  to  embryo 
abortion  after  fertilization  and  therefore  is  not  associated  with  partheno- 
carpy.  Fruits  which  the  botanist  classifies  as  accessory  are  somewhat 
more  inclined  to  parthenocarpic  development  than  those  consisting  of 
ovarian  tissues  only.  Parthenocarpy  is  no  insurance,  however,  against 
loss  of  crop  from  excessive  dropping  of  blossoms  under  certain  condi- 
tions. In  general,  seedlessness  is  valuable  from  the  commercial  stand- 
point. In  most  instances  there  is  a  distinct  correlation  between  the 
formation  of  seeds  and  the  development  of  the  fleshy  tissues  of  the  fruit — 
the  greater  the  seed  number,  the  larger  the  fruit.  Other  limiting  factors, 
however,  may  destroy  this  correlation.  Between  seed-containing  and 
seedless  fruits  of  the  same  varieties,  there  are  often  distinct  differences 
in  form,  composition  and  ripening  period.  However,  there  is  no  good 
evidence  that  the  specific  qualities  or  characteristics  of  the  pollen  variety 
are  in  any  way  stamped  upon  the  resulting  fruit. 


CHAPTER  XXX 
FRUIT  SETTING  AS  AN  ORCHARD  PROBLEM 

The  preceding  discussion  has  shown  that  certain  fruit  varieties  are 
completely  self  fruitful,  others  are  partly  self  fruitful  and  still  others  are 
self  barren.  With  varieties  definitely  known  to  be  self  fruitful  it  is  safe 
to  plant  solid  blocks  to  a  single  variety  without  making  any  provision 
for  cross  pollination.  The  heavy  production  that  characterizes  large 
plantations  of  the  Concord  grape,  the  Baldwin  apple,  the  Montmorency 
cherry,  the  Cuthbert  raspberry  and  many  other  fruits  is  sufficient  evi- 
dence on  this  point.  On  the  other  hand  many  varieties  that  are  often 
considered  self  fruitful  because  in  the  average  season  they  set  a  full  crop 
without  the  aid  of  any  foreign  pollen,  are  often  greatly  benefitted  by 
cross  pollination.  Thus  though  the  French  prune  is  generally  considered 
self  fruitful  and  there  are  many  large  orchards  consisting  exclusively  of 
that  variety,  a  higher  percentage  of  its  blossoms  set  when  cross  pollin- 
ated with  Imperial  than  when  selfed.^^  In  general  it  is  good  practice 
always  to  make  provision  for  cross  pollination  when  planting  the  orchard, 
unless  there  is  definite  knowledge  that  this  is  not  needed  for  the  variety 
when  grown  under  the  conditions  in  question.  Even  though  a  variety 
is  entirely  self  fruitful  under  a  given  set  of  conditions  the  evidence  shows 
that  in  many  cases  the  increase  in  the  size  of  fruit  resulting  from  the 
stimulus  of  cross  fertilization  is  sufficient  to  warrant  planting  together 
two  or  more  varieties  which  bloom  at  the  same  time. 

Fortunately  the  selection  of  varieties  to  secure  effective  cross  pollina- 
tion does  not  usually  add  many  complications  to  the  problem  of  variety 
selection.  In  most  fruits  the  grower  prefers  to  raise  two  or  more  varieties 
rather  than  a  single  sort.  By  choosing  those  that  ripen  at  different 
seasons  the  harvesting  problem  is  usually  greatly  simplified  and  often 
problems  of  tillage  and  spraying  as  well.  When  the  orchard  is  to  be 
planted  to  two  or  more  varieties  for  reasons  other  than  cross  pollination, 
it  is  necessary  only  to  make  a  selection  such  that  their  blossoming  seasons 
overlap  to  a  considerable  extent.  When  it  seems  best  to  have  as  large 
a  part  of  the  orchard  as  possible  consist  of  a  single  variety,  the  problem 
of  selecting  one  for  cross  pollination  purposes  is  not  materially  different 
than  before.  First  and  foremost,  its  blossoming  season  should  overlap 
that  of  the  main  sort.  Then,  questions  of  its  maturing  season,  produc- 
tiveness, market  value  and  so  on,  should  receive  due  consideration. 
Another  point  that  should  receive  attention  in  the  selection  of  a  pollenizer 

538 


FRUIT  SETTING  AS  AN  ORCHARD  PROBLEM  539 

to  be  planted  in  limited  numbers  for  the  benefit  of  a  main  sort  is  its 
pollen -bearing  qualities.  Some  varieties  are  heavy  pollen  producers; 
others  bear  only  limited  amounts.  Thus  IVIeylan  is  one  of  the  best  varie- 
ties of  the  Enghsh  walnut  and  Glen  Mary  one  of  the  poorest  strawberries 
to  plant  for  pollinating  other  varieties. 

The  Number  of  Pollenizers. — The  question  often  is  raised  as  to  the 
number  or  percentage  of  pollenizers  necessarj^  when  business  considera- 
tions make  it  desirable  to  limit  them  as  much  as  possible.  No  very 
definite  rule  can  be  given.  In  most  deciduous  tree  fruits  every  third 
tree  in  every  third  row  will  furnish  all  the  pollen  necessary  for  the  remain- 
ing 89  per  cent.  This  proportion,  however,  would  not  be  practicable  in 
the  strawberry  plantation  when  it  is  desired  to  grow  pistillate  varieties 
mainly.  Much  depends  on  the  provision  for  cross  pollinating  agents. 
If  it  is  an  insect-pollinated  plant  and  pollen-carrying  insects  are  numerous 
(say  amounting  to  one  swarm  of  bees  for  each  1  or  2  acres  of  fruit  trees) 
fewer  trees  of  the  less  valuable  pollenizers  are  necessary  than  if  the  bees 
are  few. 

In  cases  where  large  blocks  of  a  single  self  unfruitful  variety  have  been 
planted  and  the  trees  have  been  in  the  orchard  for  a  number  of  years 
much  quicker  results  can  be  obtained  by  grafting  over  some  of  them  than 
by  removal  and  replanting.  Occasionally  growers  solve  the  difficulty 
by  grafting  over  a  limb  or  two  in  each  tree,  but  this  usually  complicates 
the  problem  of  harvesting  and  from  an  economic  standpoint  is  less  satis- 
factory than  changing  the  entire  tops  of  certain  trees. 

Temporary  Expedients. — Immediate  results  are  often  obtainable  in 
self  unfruitful  orchards  through  securing  from  trees  of  other  varieties  large 
branches  containing  nvmierous  flower  buds  and  placing  them  here  and  there 
in  the  self  barren  orchard.  This  permits  pollen-carrying  insects  to  effect 
a  transfer  of  pollen  from  these  branches  to  the  pistils  of  the  orchard  trees. 
Such  branches  should  be  cut  just  as  their  flowers  are  starting  to  open  and 
stood  in  buckets  of  water  so  that  they  will  keep  fresh  while  their  flowers 
are  opening  and  shedding  pollen.  This  is  only  a  temporary  expedient, 
for  it  is  troublesome  and  often  rather  expensive ;  however,  it  has  been  the 
means  of  insuring  a  good  set  of  fruit  in  many  cases  when  there  would  have 
been  a  crop  failure  otherwise.  It  really  is  a  kind  of  artificial  pollination, 
comparable  to  practices  in  vogue  for  thousands  of  years  in  the  produc- 
tion of  dates  and  many  varieties  of  figs. 

Pollinating  Agents. — Wind  and  insects  have  been  mentioned  as  the 
chief  pollen -carrying  agencies  for  deciduous  fruits.  Of  the  two,  insects 
are  by  far  the  more  important  except  in  some  of  the  nut  crops.  In  fact 
the  amount  of  cross  pollination  effected  through  the  agency  of  the  wind 
in  apples,  pears,  peaches  and  other  insect-pollinated  fruits  is  practically 
negligible.  This  has  been  shown  experimentally  for  the  plum  by 
Waugh^^*^    and  for  other  fruits  by  other  investigators.     Among  pollen- 


540  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

carrying  insects  the  common  honey  bee  is  probably  the  most  important 
for  the  fruit  grower.  Its  importance  is  such  that  the  presence  of  an 
ample  number  should  be  insured  during  the  blossoming  season.  In 
some  of  the  cherry  growing  sections  of  the  Pacific  Northwest  growers 
make  a  practice  of  securing  colonies  of  bees  from  apiarists  to  place  in 
their  orchards  during  blossoming  and  they  find  that  the  rental  they 
pay  yields  them  a  higher  rate  of  interest  on  their  investment  than  any 
other  item  in  their  cost  of  production.  No  hard  and  fast  rules  can  be 
laid  down  regarding  the  number  of  colonies  necessary  for  effective  pol- 
lination in  an  orchard  of  a  given  size.  Much  depends  on  the  size  of  the 
trees,  their  profusion  of  bloom  and  the  number  of  hours  of  favorable 
weather  for  pollination  during  their  flowering  season  and  the  presence 
or  absence  of  other  pollen-carrying  agents.  Ordinarily  one  colony  of 
bees  to  each  1  or  2  acres  of  orchard,  depending  on  conditions,  will 
produce  satisfactory  results  and  sometimes  they  will  take  care  of  a 
considerably  larger  acreage. 

It  is  often  assumed  that  perfect  flowered  and  self  fruitful  varieties 
require  no  outside  agent  for  the  transfer  of  pollen  from  stamen  to  stigma. 
In  other  words,  the  self  fruitful  variety  is  assumed  to  be  autogamous. 
This  is  often  the  case,  at  least  to  a  certain  extent,  However,  it  has 
been  found  in  California  that  Imperial  prune  trees  from  which  bees  were 
excluded  during  the  blossoming  season  set  only  0.34  per  cent,  of  their 
blossoms,  while  trees  of  the  same  variety  accessible  to  bees  but  protected 
from  cross  pollination  from  other  varieties  set  3.02  per  cent.''^  In 
the  French  prune  19  per  cent,  of  the  blossoms  matured  fruit  where  bees 
visited  them,  while  only  0.43  per  cent,  matured  fruit  where  the  bees  were 
excluded.  Conditions  may  be  quite  different  in  other  fruits  or  in  other 
self  fruitful  varieties  of  the  plum,  but  in  the  absence  of  definite  knowl- 
edge that  the  varieties  he  is  growing  are  both  self  fruitful  and  autogamous 
the  grower  should  make  adequate  provision  for  pollen  transfer. 

The  Fruit  Setting  Habits  of  Different  Fruits. — In  the  preceding 
discussion  of  the  factors  influencing  the  setting  of  fruit  most  deciduous 
fruit  species  have  been  mentioned  along  with  certain  others.  Following 
are  summarized  statements  of  the  more  important  fruit  setting  character- 
istics of  the  common  fruits. 

Apple. — The  flowers  of  the  apple  are  true  hermaphrodites.  Occa- 
sionally defective  pistils  are  found  and  generally  a  portion  of  the  pollen 
grains  are  defective,  though  apparently  all  varieties  mature  a  certain 
amount  of  good  pollen.  i°  The  percentage,  however,  varies  with  environ- 
mental conditions.  Many  varieties  are  self  fruitful,  many  others  are 
self  barren  or  partly  so.  Lewis  and  Vincent^^  reported  about  70  per  cent, 
of  the  varieties  studied  as  self  barren  in  Oregon;  Gowen^^  found  about 
63  per  cent,  completely  self  barren  and  only  13  per  cent,  completely  self 
fruitful  in  Maine  and  Hooper^^  reported  about  two-thirds  of  the  varieties 


FRUIT  SETTING  AS  AN  ORCHARD  PROBLEM  541 

he  worked  with  in  England  to  be  self  sterile.  The  degree  of  self  fruitful- 
ness  in  the  apple  varies  greatly  with  the  age  and  vigor  of  the  trees,  the 
season,  locality  and  many  other  factors.  Thus  the  Jonathan,  which  is 
self  fruitful  in  many  parts  of  the  United  States,  is  self  fruitful  in  Victoria 
(Australia)  when  grown  on  soils  of  medium  productivity,  but  self  barren 
when  grown  on  rich  soils. '*^  Among  the  prominent  commercial  varieties 
that  are  classed  as  comparatively  self  fruitful,  at  least  in  a  number  of 
sections,  are:  Baldwin,  Ben  Davis,  Gano,  Jonathan,  Oldenburg,  Yellow 
Newtown,  Grimes,  Wagener,  Yellow  Transparent,  Willow  Twig,  Esopus, 
Stark,  On  the  other  hand,  nearly  all  of  these  varieties  have  been  reported 
partly  or  completely  self  barren  in  certain  localities  or  at  certain  times. 
Among  those  classed  as  partly  or  completely  self  barren  are:  Arkansas 
Black,  Gravenstein,  King,  Arkansas,  Maiden  Blush,  Missouri  Pippin, 
Rome,  Ralls,  Rhode  Island,  Salome,  Tolnian,  Wealthy,  Winesap  and 
York.     These  varieties,  however,  may  frequently  prove  self  fruitful. 

Young  vigorous  trees  just  coming  into  bearing  have  been  observed 
repeatedly  to  be  much  more  likely  to  drop  their  fruit  than  trees  of  the 
same  varieties  somewhat  older  and  having  the  bearing  habit  well  estab- 
lished. On  the  other  hand  old  weak  trees  frequently  bloom  verj'-  heavily 
but  set  little  or  no  fruit.  Often  this  situation  can  be  remedied  by  liberal 
applications  of  nitrate  of  soda  or  some  other  quickly  available  nitrogenous 
fertilizer  shortly  before  blossoming. 

Apple  scab  and  fire  blight  frequently  attack  the  blossoms  or  the  newly 
set  fruits  and  are  responsible  for  much  dropping  at  an  early  stage.  These 
diseases  can  be  controlled  by  proper  spraying  and  sanitary  measures 
respectively. 

Inter-unfruitfulness  has  been  reported  for  a  few  varieties,^^'  ^"^ 
particularly  some  of  those  of  the  Winesap  group;  but  a  large  body  of 
data  indicates  that  cross  sterility  is  of  very  little  importance  in  apple 
production.  With  perhaps  the  exceptions  just  noted  the  grower  may 
consider  it  safe  to  interplant  any  one  variety  with  any  other  for  purposes 
of  cross  pollination,  provided  they  bloom  at  the  same  time. 

Parthenocarpy  occurs  rather  frequently,  but  true  parthenocarpic 
varieties  are  rare. 

Pear. — The  flowers  of  the  pear,  like  those  of  the  apple,  are  true  her- 
maphrodites. So  far  as  known,  all  varieties  produce  at  least  a  certain 
amount  of  good  pollen.  However,  many  pear  varieties  are  self  barren 
because  of  self  incompatibility.  Waite^^-  reported  22  out  of  36  varieties 
as  self  unfruitful.  Among  the  more  prominent  of  this  group  are:  Anjou, 
Bartlett,  Clairgeau,  Clapp  Favorite,  Columbia,  Easter,  Howell,  Louise 
and  Winter  Nelis.  Among  the  more  important  of  the  self  fruitful 
varieties  are:  Angouleme,  Bosc,  Flemish  Beauty,  Kieffer,  LeConte, 
Seckel,  Tyson  and  White  Doyenne.  However,  Kieffer  has  been  reported 
practically  self  sterile  in  Virginia'*^  and  Bartlett  has  been  found  partly 


542  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

self  fruitful  in  certain  localities  in  California. ^^"^  It  has  been  found 
that  most  sparingly  self  fruitful  pear  varieties  generally  mature  fruits 
with  few  or  no  good  seeds  and  that  these  fruits  are  distinctly  inferior 
in  size  to  those  of  seed-bearing  fruits  of  the  same  varieties  resulting 
from  cross  pollination.  Pears  generally  should  be  so  planted  as  to 
secure  the  benefits  from  crossing. 

So  far  as  known  the  more  common  pear  varieties  are  interfruitful 
and  one  variety  is  as  good  as  another  in  cross  polhnation  if  it  blossoms 
at  the  right  period. 

Parthenocarpy  is  not  uncommon  in  pears  but  none  of  the  varieties 
of  commercial  importance  in  America  is  parthenocarpic  regularly. 

Quince. — Circumstantial  evidence  points  clearly  to  the  conclusion 
that  the  commonly  cultivated  varieties  of  the  quince  are  self  fruitful. 
This  is  supported  by  the  results  of  investigations  of  Dorsey  in  New  York 
(data  unpublished). 

Peach. — Experimental  work  with  the  peach  at  the  Missouri/^^ 
Delaware, ^^  and  Virginia^^  Stations  indicates  that  practically  all  the 
commonly  grown  varieties  are  self  fruitful.  Furthermore  there  is  no 
evidence  of  any  gain  in  size  of  fruit  from  cross  pollination.  The  grower 
is  safe,  therefore,  in  planting  entire  orchards  to  a  single  variety. 

Almond. — The  work  of  Tufts ^^g  ^^s  shown  that  all  almond  varieties 
that  were  tested  are  generally  self  sterile  under  California  conditions, 
though  in  occasional  seasons  certain  varieties  will  set  a  fairly  good  crop 
with  their  own  pollen.  This  self  unfruitfulness  is  due  to  incompatibility 
rather  than  to  imperfect  pollen,  for  the  pollen  proves  satisfactory  on  the 
pistils  of  certain  other  varieties.  Certain  varieties  were  found  also  to  be 
interbarren;  I.X.L.  and  Nonpareil  will  set  practically  no  fruit  when 
interplanted  and  the  same  is  true  for  plantings  of  Languedoc  and  Texas. 
Plum. — Plum  varieties  vary  greatly  in  their  abilities  to  mature  fruit 
without  the  aid  of  cross  pollination.  Waugh^^^'  ^^^>  ^^'^>  i"  reported 
practically  all  the  commonly  cultivated  varieties  of  the  Japanese  and 
American  species  to  be  self  sterile;  this -has  been  confirmed  by  the  inves- 
igations  of  others.^^'  ®^'  ®*'  ^^'  ^^^  On  the  other  hand,  a  considerable 
number  of  European  varieties,  including  Giant,  Green  Gage,  Italian, 
French  and  Blue  Damson  have  been  found  partly  or  completely  self 
fruitful  in  Oregon, ^^  and  Sutton^^^  reported  18  out  of  39  varieties  to  be 
fully  self  fruitful  and  five  more  partly  self  fruitful  in  England. 

Hendrickson^^  and  MarshalP^  reported  all  Japanese  varieties  tested 
as  interfruitful  and  Waugh^^^  found  both  Japanese  and  American  varieties 
generally  interfertile.  Some  exceptions,  however,  have  been  recorded. 
Thus  Whitaker  and  Milton,  both  seedlings  of  Wildgoose,  are  interbarren 
and,  curiously  enough,  both  are  fertile  with  Sophie;  however,  Sophie 
used  as  the  pistil  parent  is  fertile  with  neither.  ^^^  Dorsey"  obtained 
only  eight  mature  fruits  from  1327  flowers  of  the  Compass  pollinated 


FRUIT  SETTING  AS  AN  ORCHARD  PROBLEM  543 

with  Yellow  Egg,  while  114  flowers  set  and  matured  fruit  when  polli- 
nated with  Burbank.  Though  both  crosses  evidently  may  be  classed 
as  interfertile,  there  is  a  great  difference  in  the  degree  of  fertility  exhibited. 
Marshall, ^°  working  with  varieties  of  P.domestica,  iound  anyone  combina- 
tion to  give  as  good  set  of  fruit  as  any  other;  Sutton, ^^^  working  with  other 
varieties  of  the  same  species,  reached  the  same  conclusion,  except  that 
intersterility  appeared  in  three  varieties.  However,  two  of  these  three 
varieties  originated  as  bud  sports  from  the  third.  The  European  plums 
are  not  interfruitful  to  any  considerable  degree  with  those  of  either  the 
Japanese  or  American  groups. 

Except  for  certain  varieties  of  the  several  European  groups  known  to 
be  self  fruitful,  plums  always  should  be  planted  so  they  will  secure  the 
advantages  of  cross  pollination. 

Apparently  both  self  and  cross  unfruitfulness  in  the  plum  is  due  to 
incompatibilities  and  not  to  degeneration  of  the  pollen  or  of  the  embryo 
sacs. 

Apricot. — Experimental  data  are  not  available  on  the  pollination 
responses  of  the  apricot;  however,  circumstantial  evidence  indicates 
that  at  least  a  number  of  the  leading  varieties  grown  in  America  are 
self  fruitful. 

Cherry. — Until  a  comparatively  recent  time  cherries  have  been 
assumed  to  be  self  fruitful.  In  1915,  Gardner^"  reported  several  varieties 
of  the  sweet  cherry,  all  that  were  tested,  as  self  unfruitful  under  Oregon 
conditions  and  a  little  later  Tufts^^^  reported  a  number  of  the  same 
varieties  self  barren  in  California.  All  the  sweet  cherries  tested  have  been 
reported  self  barren  in' England. ^^^  The  conclusion  seems  warranted 
therefore  that  self  barrenness  is  the  general  rule  in  this  group.  Gardner*" 
also  found  May  Duke  self  unfruitful  in  Oregon,  but  Sutton^^^  found 
both  May  Duke  and  Archduke  partly  self  fertile  and  Late  Duke  fully 
self  fertile  in  England.  Experimental  data  on  the  sour  cherries  are  not 
available  but  Hedrick*'^  concludes  from  his  observations  that  self  fruit- 
fulness  is  the  general  rule  in  that  group. 

,  Inter-unfruitfulness  has  been  found  among  some  of  the  varieties  of 
the  sweet  cherry- — notably  Napoleon,  Lambert  and  Bing — in  both 
Oregon*"  and  California,  ^^s 

Self  unfruitfulness  and  cross  unfruitfulness  in  the  cherry  are  due  to 
incompatibilities  rather  than  to  any  structural  defects  of  pollen  or  ovules. 

Grape. — As  mentioned  already,  conditions  in  the  grape  range  all  the 
way  from  complete  self  fruitfulness  to  complete  barrenness.  Varieties 
of  hybrid  origin  particularly  are  likely  to  be  self  barren,  though  this 
condition  is  found  in  many  varieties  descended  from  a  single  species.^*'  ^^ 
Among  some  of  the  more  common  self  fruitful  varieties  may  be  men- 
tioned: Clinton,  Champion,  Concord,  Isabella,  Moore  Early,  Niagara, 
Worden,  Agawam,  Catawba,  Delaware,  Diamond  and  Norton.     Among 


544  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

those  that  are  self  unfruitful  are:  Salem,  Barry,  Brighton  and  the  follow- 
ing are  among  those  often  at  least  partly  self  fruitful :  Lindley,  Vergennes, 
Wyoming.^ 

Practically  all  the  varieties  of  the  Muscadine  group  bear  pseudo- 
hermaphroditic  flowers  and  should  have  staminate  vines  interplanted 
with  them. 

The  immediate  factor  responsible  for  self  barrenness  in  the  grape  is  the 
production  of  impotent  or  sterile  pollen  which  is  incapable  of  fertilizing 
the  ovules  of  the  same  or  of  any  other  variety.^'  ^^  Consequently  self 
barren  varieties  are  interbarren  and  partly  self  barren  sorts  are  partly 
interbarren.  Self  fertile  varieties  should  be  interplanted  with  the  self 
barren  or  partly  self  barren  kinds.  The  production  of  impotent  or 
sterile  pollen  is  associated  almost  invariably  with  curved  or  reflexed 
stamens;  good  pollen  is  produced  in  erect  stamens.  This  flower  character 
therefore  affords  an  accurate  index  to  the  degree  of  self  fruitfulness  that 
may  be  anticipated,  except  in  the  comparatively  few  parthenocarpic 
varieties. 

Many  grape  varieties  occasionally  produce  a  few  seedless  berries 
when  not  polhnated  or  when  pollinated  with  impotent  pollen.  This 
characteristic  apparently  is  aided  by  certain  practices  such  as  ringing  or 
girdhng.  In  a  few  varieties,  such  as  Thompson's  Seedless,  this  occurs 
regularly .^^  According  to  Stout,  ^^^  seedless  American  grape  varieties 
generally  produce  good  pollen,  but  since  their  "femaleness"  is  not 
strongly  developed  they  are  not  able  to  mature  good  seeds. 

Strawberry. — Strawberry  varieties  are  generally  classed  as  pistillate 
flowering  and  perfect  flowering.  Apparently  all  the  perfect  flowering 
sorts  produce  good  pollen  and  all  are  self  fruitful  and  apparently  any 
perfect  flowering  variety  may  be  planted  with  any  pistillate  flowering 
sort  for  purposes  of  cross  pollination.  Since,  however,  some  of  the  per- 
fect flowering  varieties  produce  only  small  amounts  of  pollen,  they  are 
not  ideal  pollenizers  for  pistillate  sorts.  In  general  the  later  maturing 
flowers  of  the  inflorescence,  particularly  in  the  perfect  flowering  varieties, 
are  less  fertile  than  earlier  flowers  of  the  same  cluster  and  this  pistil 
sterility  is  "expressed  in  the  production  of  irregularly  shaped  berries  or 
entirely  sterile  flowers." ^^^ 

Currant  and  Gooseberry. — Few  exact  data  are  available  on  the  polli- 
nation requirements  of  the  currant  and  the  gooseberry.  However,  field 
observation  indicates  clearly  that  the  varieties  commonly  grown  in  this 
country  are  self  fruitful  and  hence  no  provision  need  be  made  for  cross 
poflination.  Hooper^^  has  reported  all  the  varieties  of  the  English  goose- 
berry which  he  tested  to  be  self  fertile. 

The  Brambles. — Until  comparatively  recent  date  the  bramble  fruits 
have  generally  been  considered  self  fruitful.  Hooper,''^  working  with  a 
number  of  varieties  of  the  raspberry  and  with  the  loganberry  in  England, 


FRUIT  SETTING  AS  AN  ORCHARD  PROBLEM  545 

found  all  that  he  tested  self  fertile  but  reported  some  increase  in  size 
of  fruit  resulting  from  cross  pollination.  In  North  Carolina  11  out  of 
15  varieties  of  dewberries  were  found  self  barren  and  12  out  of  16  varieties 
of  blackberries  self  fruitful.  The  varieties  of  Ruhus  villosus  generally 
were  self  fruitful,  those  of  R.  trivialis  self  barren.  There  was  no  increase 
in  size  of  fruit  from  cross  pollination  in  those  varieties  maturing  fruit 
when  selfed.  The  Vineland  (Ontario)  Horticultural  Experiment  Sta- 
tion* ^^  has  reported  that  a  number  of  the  seedlings  of  the  raspberry  which 
they  have  obtained  in  their  breeding  work  are  self  sterile.  Others  are 
self  fruitful  or  partly  so.  A  number  of  the  blackberry-dewberry  hybrid 
varieties  are  partly  or  wholly  self  barren. 

The  Nuts. — Data  are  not  available  on  the  degree  of  self  fruitfulness 
characteristic  of  different  varieties  of  the  walnut,  pecan,  hickory,  chest- 
nut and  filbert.  All  are  monoecious  and  a  large  majority  are  characterized 
by  partial  dichogamy.  In  some  the  dichogamy  is  almost  complete, 
rendering  the  tree  or  variety  self  unfruitful  to  a  marked  degree.  To 
what  extent,  if  at  all,  individual  trees  or  varieties  are  self  unfruitful  because 
of  incompatibility  is  not  known.  On  account  of  the  partial  dichogamy 
that  is  generally  found  it  is  always  a  good  plan  to  interplant  two  or  more 
varieties  having  approximately  the  same  blossoming  seasons. 

Persimmon. — The  kaki,  or  Japanese  persimmon,  includes  varieties 
bearing  pistillate  flowers  only  and  those  bearing  both  pistillate  and  stami- 
nate  flowers.  Of  the  varieties  in  the  latter  class  some  bear  staminate 
flowers  regularly,  others  bear  them  sporadically.  The  names  pistillate 
constants,  staminate  constants  and  staminate  sporadics  have  been  applied 
to  these  several  groups. 

Some  varieties  set  fruit  freely  without  pollination  and  they  mature 
seedless  fruits.  Others  require  pollination  and  their  fruits  usually  con- 
tain one  or  more  seeds.  Apparently  pollination  is  not  so  essential  to  the 
securing  of  a  good  persimmon  crop  in  California  as  in  Florida. ^^ 

The  differences  in  the  size,  shape,  color,  flavor  and  season  of  maturity 
of  seed-bearing  and  seedless  persimmons  have  been  discussed  previously. 

There  is  reason  to  believe  that  most  pistillate  flowers  of  the  native 
American  persimmon  (Diospyros  virginiana)  require  pollination  from 
staminate  trees  of  the  same  species  in  order  to  set  and  mature  a  good  crop. 
The  Japanese  and  American  varieties  of  persimmon  are  not  interfruitful.^^ 

Summary. — In  the  absence  of  definite  knowledge  that  the  variety 
being  planted  is  self  fruitful  under  local  conditions  provision  should 
always  be  made  for  cross  pollination.  Even  when  varieties  are  self 
fruitful  the  increase  in  size  often  obtained  as  a  result  of  cross  pollination 
warrants  the  use  of  other  pollenizers.  In  most  tree  fruits  one  of  the 
pollenizing  variety  is  sufficient  for  8  or  10  trees  of  the  leading  sort. 
Top  grafting  and  the  use  of  flowering  branches  of  other  varieties  at  the 
blossoming  season  are  the  most  satisfactory  methods  of  providing  for 


546  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

cross  pollination  in  established  self  unfruitful  or  inter-unfruitful  orchards. 
Insects,  particularly  the  honey  bee,  are  the  most  effective  pollinating 
agents  in  the  deciduous  fruit  plantation.  There  should  be  ample  provi- 
sion for  pollen  transfer,  even  in  orchards  of  self  fruitful  varieties.  The 
fruit  setting  habits  and  polHnation  requirements  of  different  deciduous 
fruits  are  discussed. 

Suggested  Collateral  Readings 

Waite,  M.  B.  Pollination  of  Pear  Flowers.  U.  S.  D.  A.  Div.  Pom.,  Bui.  5.  1895. 
Hedrick,  U.  P.     Relation  of  Weather  to  the  Setting  of  Fruit.     N.  Y.  Agr.  Exp.  Sta. 

Bui.  299.     1908. 
Valleau,  W.  D.     A  Study  of  Sterility  in  the  Strawberry.     Jour.  Agr.  Res.       12:613- 

670.     1918. 
Dorsey,  M.  J.     Pollen  Development  of  the  Grape  with  Special  Reference  to  Sterility. 

Minn.  Agr.  Exp.  Sta.  Bui.  144.     1914. 
Eisen,  G.     The  Fig.     U.  S.  D.  A.  Div.  Pom.,  Bui.  9.     Pp.  74-128.     1901. 

Literature  Cited 

1.  d'Angremond,  A.     Flora.     107:  57.     1914. 

2.  Beach,  S.  A.     N.  Y.  Agr.  Exp.  Sta.  Bui.  157.     1898. 

3.  Beach,  S.  A.     N.  Y.  Agr.  Exp.  Sta.  Bui.  169.     1900. 

4.  Beach,  S.  A.     N.  Y.  Agr.  Exp.  Sta.  Bui.  223.     1902. 

5.  Beach,  S.  A.     Proc.  Am.  Pom.  Soc.     P.  72.     1901. 

6.  Benson,  M.  F.     Trans.  Linn.  Soc.  IL     Bot.  3:  409-424.     1894. 

7.  Bioletti,  F.  T,     Cal.  Agr.  Exp.  Sta.  Bui.  197.     1908.     (P.  Viala  and  P.  Pacottel 

cited  as  authority.) 

8.  Bioletti,  F.  T.     Cal.  Agr.  Exp.  Sta.  Cir.  191.     1918. 

9.  Booth,  N.  O.     N.  Y.  Agr.  Exp.  Sta.  Bui.  224.     1902. 

10.  Booth,  N.  O.     Proc.  Am.  Soc.  Hort.  Sci.     P.  25.     1906. 

11.  Brainerd,  E.,  and  Peitersen,  A.  K.     Vt.  Agr.  Exp.  Sta.  Bui.  217.     1920. 

12.  Brown,  F.  R.     First  Bienn.  Crop  Pest  and  Hort.  Rept.  Ore.  Agr.  Exp.  Sta. 

Pp.  41-43.     1911-12. 

13.  Brown,  W.  R.     Agr.  Res.  Inst.  Pusa  Bui.  93.     1920. 

14.  Burbidge,   F.   W.     Cultivated  Plants;  Their  Propagation   and  Improvement. 

P.  472.     Edinburgh  and  London,  1877. 

15.  Bushnell,  J.  W.     Proc.  Am.  Soc.  Hort.  Sci.     17:  47-52.     1920. 

16.  Claypole,  E.  W.     Rept.  U.  S.  Com.  Agr.     Pp.  318-321.     1887. 

17.  Close,  C.  P.     Del.  Agr.  Exp.  Sta.  Rept.     14:  99-102.     1902. 

18.  Coit,  J.  E.     Cal.  Agr.  Exp.  Sta.  Ann.  Rept.     P.  105.     1914. 

19.  Coit,  J.  E.,  and  Hodgson,  R.  W.     Cal.  Agr.  Exp.  Sta.  Bui.  290.     1918. 

20.  Condit,  I.  J.     Cal.  Agr.  Exp.  Sta.  Bui.  316.     1919. 

21.  Condit,  I.  J.     Cal.  Agr.  Exp.  Sta.  Bui.  319.     1920. 

22.  Conrad,  A.  H.     Bot.  Gaz.     24:  408-418.     1900. 

23.  Darwin,    C.     The    Variation    of    Animals    and   Plants   under  Domestication. 

2d  Edition.     1:434.     New  York,  1894. 

24.  Ibid.     2:  113.     (Cited  on  authority  of  Hildebrand.) 

25.  Ibid.     2:  115-117. 

26.  Ibid.     2:  119. 

27.  Ibid.     2:  147. 


FRUIT  SETTING  547 

28.  Ibid.     2:  152-153. 

29.  Ibid.     2:  165-169. 

30.  Darwin,  C.     Cross  and  Self  Fertilization  in  the  Vegetable  Kingdom.     Pp.  343-4. 

1895. 

31.  Davey,  A.  J.,  and  Gibson,  C.  M.     New  Phytol.     16:  147-151.     1917. 

32.  Detjen,  L.  R.     N.  C.  Agr.  Exp.  Sta.  Tech.  Bui.  11.     1916. 

33.  Detjen,  L.  R.     N.  C.  Agr.  Exp.  Sta.  Tech.  Bui.  12.     1917. 

34.  Detjen,  L.  R.     N.  C.  Agr.  Exp.  Sta.  Tech.  Bui.  17.     1919. 

35.  Detjen,  L.  R.     N.  C.  Agr.  Exp.  Sta.  Tech.  Bui.  18.     1919. 

36.  Dorsey,  M.  J.     Minn.  Agr.  Exp.  Sta.  Bui.  144.     1914. 

37.  Dorsey,  M.  J.     Genetics.     4:  417-488.     1919. 

38.  Dorsey,  M.  J.     Jour.  Agr.  Res.     17:  103-126.     1919. 

39.  East,  E.  M.,  and  Park, 'J.  B.     Genetics.     2:  505-609.     1917. 

40.  Eisen,  G.     U.  S.  D.  A.,  Div.  Pom.  Bui.  9.     1901. 

41.  Exp.  Sta.  Rec.  3:  135.     1892. 

42.  Ewert,  R.     Landw.  Jahrb.     39:  463-470.     1910. 

43.  Fairchild,  D.  G.,  and  Beach,  S.  A.     N.  Y.  Agr.  Exp.  Sta.  Rept.     11:  607-611. 

1892. 

44.  Farrell,  J.     Jour.  Agr.  Victoria.     15:  142.     1917. 

45.  Fitch,  C.  L.     Proc.  Am.  Soc.  Hort.  Sci.     11:  100.     1913. 

46.  Fletcher,  S.  W.     Cornell  Univ.  Agr.  Exp.  Sta.  Bui.  181.     1900. 

47.  Fletcher,  S.  W.     Va.  Agr.  Exp.  Sta.  Rept.     Pp.  213-224.     1909-10. 

48.  Floyd,  F.  E.     Trans.  Roy.  Soc.  Canada.  (Ser.  3)  10:  (Sec.  4)  55-61.     1916. 

49.  Gaertner,   K.  F.     Versuche  und  Beobachtungen  iiber  die  Bastardzeugung  im 

Pflanzenreich.     Stuttgart.      1849. 

50.  Gardner,  V.  R.     Ore.  Agr.  Exp.  Sta.  Bui.  116.     1913. 

51.  Goff,  E.  S.     Wis.  Agr.  Exp.  Sta.  Bui.  63.     1897. 

52.  Goff,  E.  S.     Wis.  Agr.  Exp.  Sta.  Bui.  87.     1901. 

53.  Goff,  E.  S.     Wis.  Agr.  Exp.  Sta.  Ann.  Rept.     18:  289-303.     1901. 

54.  Goodspeed,  T.  H.,  McGee,  J.  M.,  and  Hodgson,  R.  W.     Univ.  Cal.  Publ.  Bot. 

5:  439-450.     1918. 

55.  Goodspeed,  T.  H.     Address  before  General  Session  Bot.  Soc.  Am.     Chicago, 

Dec.  28,  1920. 

56.  Gowen,  J.  W.     Me.  Agr.  Exp.  Sta.  Bui.  287.     1920. 

57.  Green,  J.  R.     Phil.  Trans.  Roy.  Soc.  185  B:  385-409.     1894. 

58.  Hartley,  C.  P.     U.  S.  D.  A.,  Bur.  PI.  Ind.  Bui.  22.     1902. 

59.  Harvey,  E.  M.,  and  Murneek,  A.  E.     Ore.  Agr.  Exp.  Sta.  Bul.  176.     1921. 

60.  Hedrick,  U.  P.     N.  Y.  Agr.  Exp.  Sta.  Bul.  299.     1908. 

61.  Hedrick,  U.  P.     Cherries  of  New  York.     P.  83.     Albany,  1915. 

62.  Heideman,  C.  W.  H.     Ann.  Rept.  Minn.  State  Hort.  Soc.     23:  187-195.     1895. 

63.  Heinicke,  A.  J.     Cornell  Univ.  Agr.  Exp.  Sta.     Bul.  393.     1917. 

64.  Hendrickson,  A.  H.     Cal.  Agr.  Exp.  Sta.  Ann.  Rept.     P.  45.     1916. 

65.  Hendrickson,  A.  H.     Cal.  Agr.  Exp.  Sta.  Bul.  291.     1918. 

66.  Higgins,  J.  E.,  and  Holt,  V.  S.     Hawaii  Agr.  Exp.  Sta.  Bul.  32.     1914. 

67.  Hodgson,  R.  W.     Cal.  Exp.  Sta.  Bul.  276.     1917. 

68.  Hooper,  C.  H.     Jour.  Royal  Hort.  Soc.     37:  531-535.     1912. 

69.  Howard,  W.  L.,  and  Home,  W.  T.     Cal.  Agr.  Exp.  Sta.  Bul.  326.     1921. 

70.  Hume,  H.  H.     Proc.  Am.  Soc.  Hort.  Sci.     Pp.  88-93.     1913. 

71.  Hume,  H.  H.     Trans.  St.  Louis  Acad.  Sci.     22:  125-135.     1913. 

72.  Hume,  H.  H.     Jour.  Heredity.     5:  131.     1914. 

73.  Husmann,  G.  C,  and  Dearing,  C.     U.  S.  D.  A.,  Bur.  PI.  Ind.  Bul.  273.     1913. 

74.  Husmann,  G.  C,  and  Dearing,  C.     U.  S.  D.  A.  Farmers'  Bul.  709.     1916. 


548  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

75.  Johnson,  D.  S.     Carnegie  Inst,  of  Wash.  Pub.  269.     1918. 

76.  Kerner,   A.,   and  Oliver,   F.   W.     Natural  History  of  Plants.     2(1):  407-414. 

New  York,  1895. 

77.  Ibid.     Pp.  104-129. 

78.  Ibid.     Pp.  312-313. 

79.  Ibid.     P.  317. 

80.  Ibid.     P.  420. 

81.  Ibid.     P.  453. 

82.  Ivirchner,  O.     Jahreshefte  Ver.  f.  vaterl.  Naturk.  in  Wiirtemburg.     1900. 

83.  Kirkwood,  J.  E.     Torrey  Bui.     33:  327-341.     1906. 

84.  Knight,  L.  I.     Proc.  Am.  Soc.  Hort.  Sci.     14:  101-105.     1917. 

85.  Kraus,  E.  J.     Bienn.  Crop  Pest  and  Hort.  Rept.  Ore.  Agr.  Exp.  Sta.     1 :  71-78. 

1913. 

86.  Kraus,  E.  J.     Jour.  Heredity.     6:  549-557.     1915. 

87.  Kusano,  S.     Jour.  Coll.  Agr.  Imp.  Univ.  Tokio.     6:  7-120.     1915. 

88.  Lewis,  C.  I.,  and  Vincent,  C.  C.     Ore.  Agr.  Exp.  Sta.  Bui.  104.     1909. 

89.  Marshall,  R.  E.     Proc.  Am.  Soc.  Hort.  Sci.     16:  42-49.     1919. 

90.  Massart,  J.     Bui.  Jard.  Bot.  Brux.     1:  85-95.     1902. 

91.  Mathewson,  C.  A.     Torrey  Bui.     33:  487-493.     1906. 

92.  McClelland.     Jour.  Agr.  Res.     16:  245-251.     1919. 

93.  Millardet,  A.     Rev.  de  Viticulture.     16:  677-680.     1901. 

94.  Miyoshi,  M.     Bot.  Zeit.     52:  1-28.     1894. 

95.  Mottier,  D.  M.     Carnegie  Inst.  Wash.  Pub.     15:  174-180.     1904. 

96.  Miicke,  M.     Bot.  Ztg.  66:  1-23.     1908. 

97.  Miiller-Thurgau,  H.     Landw.  Jahrb.  Schweiz.     22:  564-597.     1908. 

98.  Munson,  W.  M.     Me.  Agr.  Exp.  Sta.  Ann.  Rept.     Pp.  29-58.     1892. 

99.  Ibid.     Pp.  218-229.     1898. 

100.  Osawa,  I.     Jour.  Coll.  Agr.  Imp.  Univ.  Tokio.     4:  83-116.     1912. 

101.  Ibid.     4:  237-264.     1913. 

102.  Parrott,  P.  J.,  Hodgkiss,  H.  E.,  and  Hartzell,  F.  Z.     N.  Y.  Agr.  Exp.  Sta.  Tech. 

Bui.  66.     1919. 

103.  Baton,  J.  B.     Doctor's  Dissertation.     Yale  University.     1920. 

104.  Popenoe,  P.  B.     Date  Growing.     P.  113.     Altadena,  Cal.     1913. 

105.  Ibid.     P.  105. 

106.  Popenoe,  W.     U.  S.  D.  A.     Bui.  542.     1917. 

107.  Powell,  G.  H.     Del.  Agr.  Exp.  Sta.  Ann.  Rept.     12:  129-139.     1900. 

108.  Price,  W.  A.     Purdue  Univ.  Agr.  Exp.  Sta.  Bui.  247.     1920. 

109.  Reed,  H.  S.     Jour.  Agr.  Res.     17:  153-165.     1919. 

110.  Reimer,  F.  C,  and  Detjen,  L.  R.     N.  C.  Agr.  Exp.  Sta.  Bui.  209.     1910. 

111.  Rept.  Vineland  (Ont.)  Hort.  Exp.  Sta.     P.  17.     1919. 

112.  Rixford,  G.  P.     U.  S.  D.  A.     Bui.  732.     1918. 

113.  Sandsten,  E.  P.     Wis.  Agr.  Exp.  Sta.  Ann.  Rept.     22:  300-314.     1905. 

114.  Sandsten,  E.  P.     Wis.  Agr.  Exp.  Sta.  Res.  Bui.  4.     1909. 

115.  Schuster,  C.  E.     Bienn.  Crop  Pest  and  Hort.  Rept.  Ore  Agr.  Exp.  Sta.     3:  44-46. 

1921. 

116.  Shoemaker,  D.  M.     Johns  Hopkins  Univ.  Circ.     21:  86-87.     1902. 

117.  Sirks,  M.  J.     Arch.  Neerland.  Sci.  Ex.  et  Nat.  (Ser.  B).     3:  20.5-234.     1917. 

118.  Stevens,  N.  E.     Bot.  Gaz.     53:  277-308.     1912. 

119.  Stewart,  F.  C,  and  Eustace,  H.  J.     N.  Y.  Agr.  Exp.  Sta.  Bui.  200.     1901. 

120.  Stout,  A.  B.     Mem.  N.  Y.  Bot.  Garden.     6:  333-454.     1916. 

121.  Stout,  A.  B.     Am.  Jour.  Bot.     4:  375-395.     1917. 

122.  Stout,  A.  B.     Jour.  Genetics.     "7:  71-103.     1918. 


FRUIT  SETTING  549 

123.  Stout,  A.  B.     N.  Y.  Agr.  Exp.  Sta.  Tech.  Bui.  82.     1921. 

124.  Stuckey,  H.  P.     Ga.  Agr.  Exp.  Sta.  Bui.  124.     191(1 

125.  Sutton,  I.     Jour.  Genetics.     7:  281-300.     1917-18. 

126.  Swingle,  W.  T.     U.  S.  D.  A.,  Bur.  PI.  Ind.  Bui.  53.     1904. 

127.  Trabut,  L.     Jour.  Heredity.     7:416.     1916. 

128.  Tufts,  W.  P.     Cal.  Agr.  Exp.  Sta.  Ann.  Kept.     P.  46.     1916. 

129.  Tufts,  W.  P.     Cal.  Agr.  Exp.  Sta.  Bui.  306.     1919. 

130.  Tufts,  W.  P.     Cal.  Agr.  Exp.  Sta.  Bui.  307.     1919. 

131.  Valleau,  W.  D.     Jour.  Agr.  Res.     12:  613-670.     1918. 

132.  Waite,  M.  B.   .  U.  S.  D.  A.,  Div.  Pom.  Bui.  5.     1895. 

133.  Waite,  M.  B.     Amer.  Agric.     75:  112.     1905. 

134.  Waugh,  F.  A.     Vt.  Agr.  Exp.  Sta.  Ann.  Kept.     10:  87-93.     1896-1897. 

135.  Ibid.     11:245.     1897-1898. 

136.  Ibid.     13:358.     1899-1900. 

137.  Waugh,  F.  A.     Plums  and  Plum  Culture.     Pp.  282-307.     New  York,  1901. 

138.  Webber,  H.  J.     U.  S.  D.  A.,  Div.  Veg.  Phys.  and  Path.  Bui.  22.     1900. 

139.  Wellington,  R.     Am.  Nat.     47:  279-306.     1913. 

140.  Wester,  P.  J.     Torrey  Bui.     37:  529-539.     1910. 

141.  White,  J.    Ann.  Bot.  21:  487-499.     1907. 

142.  Whitten,  J.  C.     Mo.  Agr.  Exp.  Sta.  Bui.  46.     1899. 

143.  Whitten,  J.  C.     Mo.  Agr.  Exp.  Sta.  Bui.  117.     1914. 

144.  Wicks,  W.  H.     Ark.  Agr.  Exp.  Sta.  Bui.  143.     1918. 


SECTION  VI 
PROPAGATION 

The  universality  of  variation  in  plants  when  propagated  sexually  is  well 
known.  Comparatively  few  are  the  fruit  plants  which  reproduce  their 
like  by  seed  with  any  great  degree  of  certainty.  Though  this  condition 
has  certain  disadvantages  it  is,  on  the  whole,  fortunate.  The  animal 
breeder  or  the  breeder  of  seed  propagated  plants,  when  he  has  obtained  a 
desirable  individual,  confronts  the  problem  of  reproducing  its  like,  of 
fixing  the  strain.  The  propagator  of  fruit  plants  facing  the  same  prob- 
lem has  a  different  solution ;  from  the  parent  plant  he  cuts  pieces  each  of 
which  produces  a  plant  practically  the  same  as  the  original.  The  problem 
of  propagation  of  fruit  plants  is  essentially  making  these  pieces  of  the 
parent  plant  live.  Sometimes  they  grow  if  thrust  into  earth;  hence, 
propagation  by  cuttings.  Again,  they  must  be  placed  on  rooted  plants 
with  which  they  can  unite;  hence,  budding  and  grafting,  which  is  in  reality 
the  placing  of  cuttings  is  another  medium. 

Though  the  conception  is  simple,  actual  practice  involves  a  seemingly 
interminable  variety  of  refinements  and  detail,  varying  with  the  climate, 
the  species,  even  the  variety  and  with  economic  conditions.  The  mere 
feasibility  of  a  given  process  does  not  demonstrate  its  expediency  and 
though  the  process  is  expedient  it  does  not  necessarily  follow  that  the 
product  is  of  lasting  value.  A  certain  stock  may  be  desirable  to  the 
nurseryman  because  it  is  cheapest,  or  most  easily  worked  or  makes  the 
best  initial  growth  and  still  it  may  not  be  well  suited  to  the  orchard. 
This  condition  may  be  reversed.  Again,  a  given  stock  may  be  entirely 
satisfactory  if  the  trees  are  planted  in  one  section  or  in  one  soil  and  totally 
unsuited  to  another  section  or  to  another  soil. 

Though  the  art  of  grafting  (the  term  as  used  in  this  discussion  in- 
cludes budding)  apparently  antedates  the  art  of  writing,  many  questions 
growing  out  of  its  application  are  far  from  answered,  at  least  so  far  as 
American  practice  is  concerned.  In  the  early  days  of  standardized  apple 
production,  when  the  seedling  orchards  were  newly  topworked  to  named 
varieties,  there  was  much  discussion  of  the  effect  of  stock  on  cion  and  of 
related  questions,  but  attention  was  soon  diverted  to  the  protection  of 
fruit  and  trees  from  pests  and  for  many  years  little  notice  has  been  given 
the  underground  parts  of  the  trees,  except  when  it  was  forced  upon 
growers  in  some  sections.     With  the  rise  of  commercial  nurseries  the 

550 


PROPAGATION  551 

newer  generation  of  fruit  growers  know  little  about  the  propagation  of  the 
trees  they  grow ;  many  do  not  know  on  what  stocks  their  trees  have  been 
worked. 

Similarly,  scientific  investigation  has  devoted  little  attention  to  these 
matters,  being  concerned  with  perhaps  more  pressing  problems.  For 
most  of  the  precise  study  in  this  field  indebtedness  must  be  acknowledged 
to  European  workers. 


CHAPTER  XXXI 
THE  RECIPROCAL  INFLUENCES  OF  STOCK  AND  CION 

Grafts  between  certain  plants  are  successful;  in  many  other  cases  the 
results  range  from  partial  success  to  utter  failure.  Sometimes  there  is 
immediate  failure  to  unite;  sometimes  the  grafts  unite  but  the  death  of 
either  cion  or  stock — generally  the  cion — occurs  in  a  short  time;  again 
the  grafted  parts  may  unite  but  there  will  be  an  ultimate  failure  in  stock 
or  in  cion.  On  the  other  hand,  as  with  apricot  on  plum  and  on  peach  in 
New  York,  plants  may  live  a  considerable  time  and  function  fairly  well, 
under  favorable  conditions,  without  a  very  successful  union  of  stock  and 
cion  and  it  is  only  an  untoward  incident,  such  as  a  high  wind,  that  reveals 
the  defective  union.  Sometimes  a  certain  combination  can  be  made 
with  one  kind  of  graft  and  not  with  others — the  approach  graft  frequently 
succeeds  when  others  fail.  Finally,  though  a  certain  combination  of 
stock  and  cion  may  be  successful  it  is  not  inevitable  that  a  reciprocal 
combination  will  succeed. 

The  capricious  occurrence  of  successful  and  of  unsuccessful  combina- 
tions in  grafting  follows  no  well  defined  law.  Jost^^  states  the  cases 
must  be  accepted  as  they  occur;  they  are  not  to  be  explained.  DanieP" 
explains  most  of  them  by  the  degree  of  correspondence  of  "functional 
capacity"  of  stock  and  cion,  i.e.,  that  there  must  be,  for  a  successful 
graft,  a  certain  relative  similarity,  qualitatively  and  quantitatively,  in 
their  requirements  for  water  and  food  and  in  their  general  habits  of 
growth. 

Botanical  relationship,  as  understood  by  closeness  in  the  system  of 
classification,  is  a  fair  guide  to  probable  congeniality  but  it  is  by  no  means 
infallible.  Horticultural  varieties  of  exogenous  plants  generally  may  be 
intergrafted  freely,  species  somewhat  less  so,  genera  only  occasionally 
and  families  only  rarely.  Nevertheless,  the  pear  and  the  apple  form  a. 
less  congenial  combination  than  the  pear  and  the  quince  though  the 
pear  is  more  closely  related  to  the  apple  than  to  the  quince.  Sahut^^^ 
states  that  the  pear  works  on  quince  more  readily  than  Portugal  quince 
on  quince. 

THE  CONGENIALITY  OF  GRAFTS 

Shoots  of  potato  succeed  better  on  Datura  and  Physalis  than  on 
many  species  of  the  genus  Solarium.  According  to  Sahut^^s  Carriere 
grafted  Garrya  elUptica  Dougl.  on  Aucuha  japonica,  thus  uniting  members 

552 


THE  RECIPROCAL  INFLUENCES  OF  STOCK  AND  CI  ON         553 

of  different  families.  Biffen^^  succeeded  in  grafting  Trifolium  pratense 
on  Anthyllis  vulneraria,  of  a  different  genus. 

Dawson^^  cited  some  interesting  cases:  "The  Photinia  allied  to  the 
beam  tree  (Pyrus  Aria)  and  the  Eriobotrya  [loquat],  allied  to  the  medlar, 
both  evergreens,  will  graft  on  the  medlar  and  not  on  the  hawthorn. 
Cotoneasters,  amelanchiers  and  Pyrus  Aria  all  do  well  on  hawthorn  and 
last  longer  but  make  slower  growth  than  on  mountain  ash.  Pyrus 
arbutifolia  grafts  well  as  a  standard  on  mountain  ash.  ;  .  .  Pyrus 
Toringo  .    .    .  will  grow  on  seedlings  but  are  better  on  Pyrus  haccata." 

Manning^°^  listed  several  cases  of  incompatibility  in  close  relatives. 
The  laburnum,  he  stated,  would  not  take  on  locust.  Flowering  dogwood 
on  cornelian  cherry  (both  in  the  genus  Cornus)  made  only  short-lived 
unions.  The  Josika  lilac  was  said  to  succeed  on  the  ash  while  the  Persian 
lilac  failed,  though  it  grew  on  the  common  lilac.  Coulter'*^  states  that 
Prumis  Padus  and  P.  Laurocerasus  show  a  lack  of  affinity.  Native,  Japa- 
nese and  European  plums  take  readily  on  western  sand  cherry,  though 
sweet  and  sour  cherries  unite  with  it  much  less  readily." 

The  gooseberry  will  grow  on  Ribes  aureum  but  not  on  the  cultivated 
edible  currants. ^^  Some  varieties  of  pears  unite  readily  with  quince 
stocks,  but  others  are  so  conspicuously  defective  in  uniting  that  they 
necessitate  a  resort  to  double  working. 

Berckmanns^"  reported  that  Labrusca  and  Aestivalis  grapes  inter- 
worked  readily  but  that,  apparently  because  of  the  difference  in  the 
texture  of  the  wood,  Labrusca  varieties  would  not  take  on  Vulpina. 
Bioletti^^  recognizes  certain  of  the  Vinifera  group  of  grapes  as  having 
"defective  affinity"  in  that  they  do  not  unite  at  all  well  with  the  stocks  in 
common  use;  he  recommends  a  special  stock  for  these  varieties  because  it 
makes  an  excellent  union  with  them.  Among  these  varieties  he  lists 
Emperor,  Ferrara,  Cornichon,  Muscat,  Mataro,  Folle  Blanche,  Pinot, 
Gamay,  Gutedel;  the  stock  recommended  for  them  is  known  as  1202. 

Brown^s  cites  a  case  in  California  in  which  both  cion  and  stock  grew 
larger  than  their  customary  size.  "Almonds  grafted  on  peaches,"  he 
states,  "have  developed  a  circumference  of  a  little  less  than  10  feet,  while 
the  maximum  size  of  either,  growing  alone,  would  be  scarcely  5  feet. 
Where  almonds  are  grafted  on  plum  stock,  the  reverse  is  true."  Measure- 
ments are  cited  showing,  in  the  almond  on  peach,  a  circumference  of  9 
feet  1  inch  above  the  graft  and  10  feet  4  inches  below,  while  the  almond 
on  plum,  of  equal  age  with  the  first  combination,  measured  4  feet  below 
the  union  and  4  feet  10  inches  above. 

Other  stone  fruits  exhibit  similar  capriciousness.  In  Vermont  the 
Newman  plum  seemed  to  have  much  greater  affinity  for  peach  roots  than 
did  Green  Gage,  Stoddard,  Chabot  or  Milton;  in  fact  the  last  three  did 
very  poorly  on  peach  stock.  ^^^  In  California  certain  prunes,  including 
Robe  de  Sargent,  Imperial  Epineuse  and  Sugar,  lack  affinity  for  the 


554  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

peach  root;  on  the  ahnond  the  last  two  take  well  but  the  first  is  again 
refractory. '24  'pj^g  Yellow  Egg,  Jefferson  and  Washington  plums  also 
lack  affinity  for  peach  roots.  1^4  Wiskeri^^  g^^j^g  Diamond  and  Grand 
Duke  to  this  list.  Sugar,  mentioned  above  as  failing  on  peach,  succeeds 
on  apricot,  while  the  French  prune  fails  on  the  latter  stock. ^^ 

Swingle'^"  calls  attention  to  the  lack  of  compatibility  between  the 
Satsuma  orange  and  the  sour  orange  stock.  On  the  sweet  orange,  growth 
is  satisfactory  but  the  fruit  is  poor;  by  far  the  best  results  are  secured  on 
trifoliate  stock.  The  kumquat  unites  with  the  sour  orange  but  dies 
after  starting  growth,  though  on  trifoliate  stock  it  gives  very  satis- 
factory results.  Bonns^''  reported  the  trifoliate  to  be  distinctly  dwarfing 
for  lemon,  much  more  so  than  for  orange. 

Apple  varieties  show  various  degrees  of  congeniality  with  dwarfing 
stocks.  Hedrick^^  reported  Mcintosh,  Wealthy  and  Lady  to  be  the  most 
congenial  of  a  large  number  of  varieties  tested,  and  Jonathan,  Esopus, 
Grimes,  Alexander,  Wagener,  Boiken  and  Bismark  as  "very  satisfactory." 
Baldwin,  Rhode  Island,  Rome,  Ben  Davis  and  Northern  Spy  were  uncon- 
genial and  Twenty  Ounce  gave  the  poorest  results. 

Mclntosh^^^  is  said  to  make  a  strong  growth  as  a  young  tree  on  cion- 
rooted  Transcendent  Crab,  though  Red  Astrachan  is  markedly  dwarfed 
on  the  same  stock. 

Maynard'"^  described  a  case  which  may  be  considered  to  have  a 
bearing  on  the  present  question.  It  was  reported  as  follows:  "About 
10  years  ago  six  small  trees  of  yellow  Siberian  crab  and  three  of  Williams' 
Favorite  were  planted  as  represented  in  the  following  diagram,  S  indicat- 
ing Siberian   crab,   S.B.  the  same  budded  and  W  Williams'  Favorite; 

S    W    S.B.    S     W    S.B.    S     W    S.B. 

"The  trees  were  all  of  the  same  size  as  nearly  as  could  be  selected 
and  every  third  tree  in  the  row  was  top-budded  with  the  Williams' 
Favorite.  The  buds  all  grew  well  the  first  season,  but  the  subsequent 
growth  was  very  little  and  at  the  end  of  10  years  all  were  dead.  The 
diameters  of  the  three  Siberian  crabs  were  4,  4}-^  and  6  inches,  of  the  three 
Williams'  Favorite  3%,  3  and  3  inches,  while  none  of  the  budded  trees 
reached  over  %  of  an  inch."  It  is  difficult  to  decide  whether  this  is  a 
case  where  the  cion  influences  stock  or  stock  influences  cion  but  the  fact 
is  worthy  of  record  here. 

Reciprocal  or  inverse  grafts  are  not  always  equally  successful.  This 
may  be  due  in  part  to  lack  of  adaptability  rather  than  to  a  lack  of  affinity, 
but  there  appears  at  times  to  be  a  real  lack  of  congeniality  in  a  graft 
whose  opposite  is  congenial.  In  some  of  Daniel's  work  the  grafts  of 
pimento  on  tomato  seemed  rather  less  successful  than  those  of  tomato  on 
pimento.^^  Sahut'^''  states  that  the  Mahaleb  succeeds  as  a  cion  on  no 
other  cherry  though  it  is  the  standard  stock  for  the  sour  cherry  in  America 


THE  RECIPROCAL  INFLUENCES  OF  STOCK  AND  CI  ON  555 

and  that  the  pear  does  better  on  the  apple  than  the  apple  on  the  pear. 
Baltet  states  that  medlar  does  well  on  quince  but  the  quince  fails  on 
medlar;  the  same  holds  true  with  quince  on  hawthorn  and  vice  versa. 
Sweet  cherry  on  sour  cherry  is  more  successful  than  the  reverse 
combination.^^ 

Tufts  states:  "  .  .  .it  has  been  the  experience  of  certain  growers 
in  the  Vacaville  section,  California,  that  practically  all  the  varieties  of 
Japanese  plums  will  work  satisfactorilj'-  with  domestica  varieties.  How- 
ever .  .  .  the  insertion  of  European  plum  scions  on  Japanese  plums 
does  not  always  result  in  a  satisfactory  union.  It  has  been  found  that 
plum  orchards,  where  worked  over  to  Japanese  varieties,  could  not  be 
worked  back  to  European  varieties  unless  all  the  Japanese  wood  was 
taken  from  the  tree."^*^ 

Similar  contrasts  in  reciprocal  grafts  occur  in  the  combination  of 
various  evergreen  on  deciduous  plants.  There  are  numerous  instances 
of  at  least  passable  success  in  grafts  of  this  sort,  but  the  inverse  combina- 
tion, deciduous  on  evergreen,  is  almost  invariably  a  failure. 

Congeniality  and  Adaptability  Distinguished. — Distinction  should  be 
made  between  congeniality  and  adaptability.  The  former  term  refers 
to  the  degree  of  success  of  the  union  between  stock  and  cion;  the  latter 
term  to  the  relation  of  the  combined  parts  to  environment,  most  often 
to  soil  and  climate.  Husmann's  conception  of  perfect  congeniality 
in  grapes  is  a  condition  in  which  "a  variety  grafted  on  another  behaves  as 
if  the  stock  were  grafted  with  a  scion  of  itself,  the  union  being  perfect  and 
the  behavior  of  the  vine  the  same  as  that  of  an  entire  ungrafted  plant. "^* 
He  states  also,  "When  both  stock  and  scion  are  suited  to  the  conditions, 
but  will  not  thrive  when  grafted,  congeniality  is  lacking."  Further: 
"The  adaptability  of  varieties  to  soil,  climates  and  other  conditions  can 
often  be  closely  forecasted,  but  congeniality  has  to  be  determined  by 
actual  test." 

Congeniality  and  adaptability  are  sometimes  differentiated  only 
with  difficulty,  as  is  shown  by  the  following  quotation  from  Blunno:^^ 
"In  France,  however,  it  was  found  that  the  yield  of  the  French  vines 
grafted  on  du  Lot  was  low;  our  experience  is  exactly  the  same  at  the 
Viticultural  Station,  Howlong  [New  South  Wales] — the  wine-grape 
varieties  grafted  on  this  stock  are  the  poorest  croppers  of  all.  In  Sicily, 
however,  the  affinity  between  the  native  European  vines  and  the  Rupe- 
stris  du  Lot  seems  to  be  perfect  and  the  yield  is  heavy.  In  this  state  the 
principal  wine-grapes  are  French  varieties  and  this  explains  how  our  ex- 
perience with  vines  on  Rupestris  du  Lot  as  poor  croppers  is  similar  to 
that  in  France." 

The  most  congenial  combination  is  not  necessarily  the  most  successful, 
as  is  shown  by  an  experience  in  New  York,  citied  by  Bailey.^  Plum 
and  peach  stocks  failed  to  make  satisfactory  unions  with  the  apricot 


556 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


and  sometimes  the  trees  were  broken  at  the  union  by  high  winds.  Worked 
on  apricot  roots,  the  apricot  made  a  better  union  and  few  trees  were 
lost  through  breaking  off;  nevertheless  in  spite  of  the  congeniality  of  this 


combination,  the  death  rate  of  these  trees  was  higher  than  that  of  apricots 
on  other  stocks.  This  evidently  is  a  case  of  a  lack  of  adaptability  being 
the  limiting  factor.  Budd^^  reported  similar  lack  of  adaptability  between 
Russian  apricots  and  plums.     In  this  case  some  of  the  trees  died  without 


THE  RECIPROCAL  INFLUENCES  OF  STOCK  AND  CION  557 

breaking  off,  death  being  due  to  the  failure  of  the  roots  to  receive  enough 
elaborated  food  from  above,  though  the  tops  seemed  not  to  suffer  greatly 
till  the  root  systems  collapsed.  Paul  C.  Stark  reports  the  peach  a  much 
better  stock  for  apricot  than  plum.  In  California  there  appears  to  be 
little  difficulty  in  effecting  union  between  apricot  cion  and  peach  or  plum 
stock,  but  the  almond  stock  proves  recalcitrant.^^*  In  France  certain 
plum  stocks  are  used  in  the  north  but  farther  south  success  is  attained 
with  ahftond,  apricot  and  peach  stocks  as  well  as  plums.  Evidently 
the  same  difficulty  is  experienced  with  almond  stock  near  the  Mediter- 
ranean, for  Baltet  described  a  double  working  when  this  stock  was 
used.i" 

From  India  is  reported  an  interesting  case.  Brown, ^^  trying 
numerous  stocks  for  Malta  and  Satsuma  oranges,  found  extraordinary 
differences  in  the  behavior  of  the  sam'e  variety  on  different  stocks  and 
of  the  same  stock  worked  to  different  variaties.  For  the  Malta  orange 
the  "rough  lemon"  gave  greatest  vigor  and  fruitfulness,  the  "sweet 
lime"  was  suitable  only  to  amateur  growing,  producing  a  small  tree  with 
a  few  oranges  of  high  quality,  while  the  citron  and  sour  orange  were 
unsuitable.  On  the  other  hand  the  Satsuma  orange  gave  best  results 
on  the  sweet  lime;  the  rough  lemon  and  citron  proved  unsuitable. 
Figures  56,  57  and  58  show  clearly  differences  associated  with  the  influ- 
ence of  stock  on  cion  and  of  cion  on  stock.  It  is  noted  by  Brown  that 
his  results  are  not  in  accord  with  American  experience,  particularly  in 
the  poor  growth  with  the  sour  orange  as  a  stock  for  the  Malta  orange. 
The  Satsuma  on  the  same  stock  was  satisfactory,  completely  reversing 
the  results  obtained  in  California. 

This  situation  seems  analagous  to  that  just  outlined  for  grapes  and 
suggests  that  adaptability  and  possibly  congeniality  may  be  operative 
in  producing  these  striking  differences  and  contradictions. 

THE  INFLUENCE  OF  STOCK  ON  CION 

The  recognition  of  dwarfing  stocks  is  assertion  of  the  effects  of  the 
stock  on  the  cion;  the  recognition  of  the  utility  of  grafting  is  acquies- 
cence in  the  independence  of  the  cion.  At  first  glance  the  question 
seems  to  hang  on  both  horns  of  the  dilemma. 

Stature. — At  the  outset  the  dwarfing  effects  of  certain  stocks,  such 
as  the  quince  on  the  pear,  the  Paradise  and  Doucin  apples  on  the  standard 
apples,  the  Sand  Cherry  on  plums  and  sundry  others  must  be  conceded 
as  evidence  of  the  effect  of  the  stock  on  the  cion. 

Parenthetically  it  may  be  stated  that  much  of  the  conflicting  evidence  con- 
cerning quince  stock  is  due  to  the  different  kinds  of  quince  used.  Barry,  as 
early  as  1848,  noted  a  mixing  of  quince  stocks  as  received  from  French  nurseries.  ^^ 
Apparently  in  England  at  present  the  situation  is  very  much  confused.^^ 


558 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Dwarfing  effects  are  most  evident  and  best  known,  but  others  occur. 
In  general  the  top  of  a  grafted  tree  tends  to  assume  a  size  equal  to  that 
of  the  top  which  the  stock  would  have  formed  if  ungrafted.     There  are, 


■>  So 


however,  exceptions  and  qualifications.  Northern  Spy,  itself  a  vigorous 
grower,  tends  somewhat  to  dwarf  many  other  varieties  worked  on  its 
roots.  13*     Some   varieties  of  apple  form   characteristically  small  trees, 


THE  RECIPROCAL  INFLUENCES  OF  STOCK  AND  CI  ON 


559 


while  others  assume  large  stature,  both  worked  on  similar  stock.  Certain 
dwarf  varieties  of  peach  remain  dwarfed  regardless  of  the  stock  on  which 
they  are  worked. 

On  the  other  hand,  some  plants  attain  greater  size  on  roots  other 
than  their  own.  The  common  lilac  is  said  to  be  greatly  increased  in 
stature  on  the  ash,  though  this  is  a  short  lived  graft.  Similar  increases 
are  said  to  obtain  when  Pinus  Gerardiana  is  worked  on  P.  sylvestris, 
incense  cedar  on  common  cedar^'*^  and  in  herbaceous  grafts,  as  in 
Phy salts  on  potato,  Arabis  alhida  (rock  cress)  on  Brassica  oleracea 
(cabbage,  etc.,)  and  Solanum  dulcamara  (bitter-sweet)  on  S.  ly coper sicum. 

Rose  acacia  is  considered  to  grow  larger  on  Eobinia  viscosa;  likewise 


iiitii 


\\  ih 


iiiLM'  Mil  f  1  ('///  '//(,  sour 
oraMgc  (,"  kluUt;i "  ul  India)  ;  ii;:ihl,  saiuu  on  (.'.  LitiLumnn,  lough  lenioa  (,  khaiiia  '  uf  India). 
Twenty-seven  months  planted.      (After  W .  Robertson  Brown.^^) 

the  dwarf  double-flowering  almond  on  peach. ^"^  Magnolia  glauca 
(swamp  bay)  is  reported  to  attain  three  times  its  normal  size  when 
grafted  on  M.  acuminata  (cucumber  tree),  though  this  has  been  suggested 
as  due  to  the  lack  of  adaptation  to  ordinary  soil  in  the  root  of  the  former, 
which  is  a  bog  plant. 

It  is  stated  that  Grimes  and  Winesap  apples  increase  in  vigor  when 
worked  on  vigorous  stocks."^  A  similar  influence  is  exercised  by 
American  persimmon  on  Japanese  persimmon  cions.*^  Prunus  pumila 
(sand  cherry)  makes  an  increased  growth  on  plum  stock. ^^  Among 
growers  of  Vinifera  grapes  the  Rupestris  St.  George  (du  Lot)  stock  is 
generally  known  to  induce  unusually  vigorous  growth  in  varieties  worked 
upon  it  and  skilful  vignerons  recognize  this  difference  when  pruning. 

Hedrick^^  reports  an  experiment  in  which  a  number  of  grape 
varieties  more  or  less  grown  in  the  grape  regions  of  New  York  were  studied 


560 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


on  three  stocks;  Clevener,  a  Labrusca-Riparia  hybrid,  grown  in  New 
York  as  a  direct  producing  wine  grape,  Rupestris  St.  George  (or  du  Lot),  a 
stock  obtained  through  Cahfornia  from  France  and  Riparia  Gloire,  also 
a  repatriated  American.  It  should  be  borne  in  mind  that  all  the  cion 
varieties  are  commonly  grown  in  this  section  as  direct  producers,  i.e., 
on  their  own  roots.  In  almost  every  case  at  least  one  of  the  stocks  used 
caused  a  marked  increase  in  vigor  over  that  of  the  cion  variety  on  its 
own  roots.  Table  1,  condensed  from  Hedrick's  data,  shows  the  growth 
ratings  of  several  varieties  as  direct  producers  and  on  the  various  stocks. 
This  growth  rating  should  be  distinguished  from  total  growth  since 
Hedrick  states  distinctly  that  the  grafted  made  less  wood  growth  than 
the  ungrafted  vines. 


Table  1. — Relative  Growth  Rating  of  Grape  Varieties  on  Different  Stocks 

IN  1910 

(After  Hedrick-'^) 


Variety 


Own  roots        St.  George 


Gloire 


Clevener 


Brighton 

Campbell , 

Catawba 

Concord 

Delaware 

Herbert 

lona 

Niagara , 

Vergennes 

Worden 

Average  20  varieties 


55.0 
17.3 
40.0 
46.0 
46.0 
64.6 
26.8 
53.9 
44.1 
26.1 


40.0 


56.0 
62.1 
74.0 
94.0 
60.0 
87.5 
45.6 
84.5 
77.8 
36.0 


63.2 


73.7 
54.6 
70.0 
90.7 
68.7 
87.1 
43.0 
57.5 
69.2 
61.6 


65.2 


75.0 
35.0 
81.6 

81.6 


56.4 
90.3 
38.1 


67.9 


In  general,  when  a  symbiotic  relation  between  stock  and  cion  exists  at 
all,  there  is  apparently  a  tendency  toward  a  balance  between  the  two. 
The  influence  is  relative.  A  dwarfing  stock  is  dwarfing  because  of  the 
limitations  on  its  development  relative  to  the  top.  There  is  nothing 
inherent  which  impels  it  to  dwarf  all  tops  worked  on  it.  As  an  example 
the  quince  may  be  considered.  It  obviously  dwarfs  pears  in  general, 
yet  it  is  said  to  increase  the  vigor  of  Cratcegus  glabra  Thunb.^^*  while  its 
dwarfing  effect  on  the  loquat  is  slight  or  absent. ^^ 

Form. — Closely  related  to  vigor  of  growth,  possibly  interwoven  with 
it,  is  form  or  habit  of  growth.  According  to  Loudon,  ^°^  "Cerasus  canaden- 
sis," naturally  a  rambling  shrub,  assumes  an  upright  habit  when  grafted 
on  the  common  plum,  while  Tecoma  radica7is  on  catalpa  forms  a  round 
head  with  pendent  branches.  Garry  a  elliptica,  Sahut  states, '^°  grafted 
on  Aucuha  branches  less.     Chamcecyparis  obtusa  pygmcea,  according  to 


THE  RECIPROCAL  INFLUENCES  OF  STOCK  AND  CION  561 

Burbidge,^®  worked  on  C.  Boursieri,  grows  erect,  while  on  Biota  or  Thuya, 
or  if  grown  from  cuttings,  it  spreads  horizontally  on  the  ground.  The 
same  writer  quotes  Briot  to  the  effect  that  the  Lihocedrus  tetragona  is 
changed  from  a  narrow  cyUndrical  column  to  a  wide-spreading  form  by 
working  on  Saxegothcea. 

Among  fruit  plants,  the  plum  and  peach  have  been  cited  as  showing 
in  the  habit  of  their  tops  the  influence  of  the  stocks  on  which  they  are 
growing. 

Knight**^  described  this  influence:  "The  form  and  habit  which  a 
peach  tree  of  any  given  variety  is  disposed  to  assume,  I  find  to  be  very 
much  influenced  by  the  kind  of  stock  on  which  it  has  been  budded;  if 
upon  a  plum  or  apricot  stock,  its  stem  will  increase  in  size  considerably, 
as  its  base  approaches  the  stock,  and  it  will  be  much  disposed  to  emit 
many  lateral  shoots,  as  always  occurs  in  trees  whose  stem  tapers  consider- 
ably upwards:  and,  consequently,  such  a  tree  will  be  more  disposed  to 
spread  itself  horizontally,  than  to  ascend  to  the  top  of  the  wall,  even  when 
a  single  stem  is  suffered  to  stand  perpendicularly  upwards.  When, 
on  the  contrary,  a  peach  is  budded  upon  the  stock  of  a  cultivated  variety 
of  its  own  species,  the  stock  and  the  budded  stem  remain  very  nearly 
of  the  same  size  at,  as  well  as  above  and  below,  the  point  of  their  junction. 
No  obstacle  is  presented  to  the  ascent,  or  descent,  of  the  sap,  which 
appears  to  ascend  more  abundantly  to  the  summit  of  the  tree.  It  also 
appears  to  flow  more  freely  into  the  slender  branches,  which  have  been 
the  bearing  wood  of  preceding  years;  and  these  extend  themselves  very 
widely,  comparatively  with  the  bulk  of  the  stock  and  large  branches." 

Comparing  the  growth  of  the  Milton  plum  on  various  stocks,  Waugh^^^ 
reported:  "The  trees  of  this  variety  growing  on  Wayland  roots  are 
upright  narrowly  vase-form,  with  relatively  few  large  branches.  They 
are  almost  as  narrow  headed  as  typical  trees  of  Abundance  or  Chabot. 
On  Marianna  roots,  in  the  very  next  row,  the  trees  of  Milton  are  low, 
round-headed,  bushy,  with  thick-spreading,  drooping  tops,  much  Hke 
trees  of  Marianna.  If  anything,  they  exaggerate  the  typical  character 
of  the  Marianna  head.  Moreover,  the  leaves  are  several  shades  darker 
and  glossier  and  the  twigs  are  dark  red  instead  of  being  green  as  in  trees 
of  the  same  variety  growing  on  Wayland  roots.  On  Americana  Milton 
has  almost  the  same  characters  as  on  Wayland." 

Somewhat  later  Stewart,^^^  describing  these  same  trees,  wrote:  "At  the 
present  time  the  differences  in  color  of  foHage  and  bark  of  young  twigs  are  not 
noticeable,  neither  is  the  '  upright  narrowly  vase-form '  head  of  Milton  on  Way- 
land  anywhere  near  so  pronounced.  Notwithstanding  these  modifications,  how- 
ever, there  is  still  a  marked  difference  in  the  habit  of  growth  of  the  trees  upon 
Wayland  and  Marianna  stocks.  On  Wayland  the  habit  of  growth  is  more  or 
less  upright,  whereas  on  Marianna  the  head  is  low,  bushy  and  spreading.  Doubt- 
less, as  the  trees  grow  older,  these  differences  will  tend  to  become  less  marked." 


562  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Rough  lemon  stock  is  said  to  produce  tall  upright  trees  of  the  varieties 
worked  on  it.-*^ 

Seasonal  Changes. — In  the  orchard  or  vineyard,  cultural  practices 
have,  in  the  majority  of  cases,  no  very  obvious  influence  on  the  time  of 
starting  growth,  but  the  effect  on  ripening  and  maturity  is  more  marked. 
The  classical  experiment  of  introducing  a  vine  or  a  branch  of  a  tree  into 
a  warmed  room  during  the  winter,  keeping  its  connection  with  the  parent 
stock  and  observing  it  start  growth  while  the  remainder  of  the  plant  is  still 
dormant,  would  lead  to  the  inference  that  the  cion  is  practically  indepen- 
dent of  the  stock  in  the  spring  flush  of  growth.     So  it  proves  in  most  cases. 

End-season  Effects.  Ripening  of  Fruit. — Concerning  effects  at  the 
other  end  of  the  growing  season  there  is  some  conflict  of  evidence.  It  is 
rather  well  known  that  some  of  the  annual  species  of  Convolvulacese 
become  perennial  when  grafted  on  perennial  species."  Daniel  reports 
that  by  grafting  the  annual  parts  of  certain  perennials  on  certain  other 
perennial  plants  he  has  succeeded  in  prolonging  the  life  of  the  cions.*^ 
Conversely,  in  some  instances,  cions  of  perennials  grafted  on  annual 
stocks  have  died  at  the  usual  time  for  the  stocks,  though  Lindemuth^^  has 
shown  a  case  where  the  plant  lived  longer.  Such  instances  as  these  are 
more  striking  than  those  observed  in  fruit  plants,  where  the  possibility  of 
change  is  necessarily  more  limited.  It  is  sometimes  claimed  that  grafting 
in  itself  hastens  maturity  in  grapes  by  a  few  days.  Cole^"  states  that 
several  growers  in  Victoria  claim  a  few  days  earlier  ripening  in  peaches 
worked  on  almond  than  on  peach  stock,  while  in  France  Sahut^^"  claims 
that  the  Myrobolan  plum  induces  earlier  ripening  in  peaches  than  does 
almond  stock.  Sahut  states  also  that  cherries  ripen  earlier  on  Laurocera- 
sus  than  on  ordinary  cherry  seedlings  and  the  Reine  Claude  plum  on 
Damas  is  said  to  be  somewhat  earlier  than  on  St.  Julien.  Cole  reports 
that  heavy  autumnal  rains  in  Victoria  are  not  so  likely  to  induce  second 
growth  or  fall  blossoming  in  plums  worked  on  Marianna  roots  as  in  those 
worked  on  Myrobolan  and  attributes  this  to  the  early  dormancy  of  the 
former  stock. 

In  America  topworked  trees  were  more  common  formerly,  propor- 
tionately at  least,  than  they  are  now  and  discussions  of  mutual  influences 
were  correspondingly  more  frequent.  These  discussions  show  a  sur- 
prising variety  of  experience  and  opinion,  particularly  in  the  effect  of  the 
stock  on  the  time  of  ripening  of  fruit  in  the  autumn.  Diametrically 
opposite  results  apparently  come  from  identical  combinations  of  stock 
and  cion.  Hovey  recounted  extensive  combinations  of  early  pears  on 
late  and  vice  versa  in  Massachusetts,  without  any  change  from  the  usual 
season  of  ripening.  There  was,  however,  rather  good  evidence  that 
plums  on  Myrobolan  ripened  earlier  than  on  late  plums.  In  apples, 
Shaw  states  that  "particularly  with  Rhode  Island  Greening  the  season  of 
ripening  is  influenced  by  the  stock." ^^^ 


THE  RECIPROCAL  INFLUENCES  OF  STOCK  AND  CI  ON 


563 


The  trifoliate  stock  is  generally  conceded  to  secure  early  ripening  in 
oranges.  Florida  experience  seems  to  indicate  that  oranges  on  rough  lemon 
stock  cannot  be  held  on  the  trees  as  long  as  when  grafted  on  sour  orange.^" 

The  grape,  however,  supplies  the  best  examples  of  stock  influence  on 
fruit  ripening.  Wickson  states  that  the  Riparias  Gloire  and  Grand  Glabra 
induce  ripening  one  to  two  weeks  ahead  of  Rupestris  St.  George.  Hed- 
rick  found  that  many  American  grapes  on  Gloire  and  Clevener  stocks 
consistently  ripen  their  fruit  ahead  of  the  same  varieties  on  their  own 
roots.  In  the  St.  George  there  was  less  uniformity  of  effect;  in  fact  this 
stock  seemed  to  retard  the  ripening  of  some  varieties.  This  difference  of 
a  few  days  is  likely  to  assume  considerable  practical  importance  with 
late  varieties  in  regions  where  autumnal  frosts  come  early  or  where 
autumnal  rains  are  frequent. 

Husmann^^  considers  that  the  degree  of  congeniality  between  cion  and 
stock  influences  the  time  of  ripening.  From  this  point  of  view  it  may  be 
inferred  that  the  same  stock  may  have  a  retarding  effect  on  one  variety 
and  hasten  the  ripening  of  another.  Much  conflicting  evidence,  in  other 
fruits  besides  grapes,  may  be  reconciled  in  this  way. 

Table  2,  including  data  taken  more  or  less  at  random  from  Husmann's 
figures,  indicates  that  this  possibility  may  be  realized.  Taking  Lenoir  as 
the  standard,  grapes  on  St.  George  have  ripened,  in  one  case  4  days  ahead,  in 
another  case  9  days  after,  Lenoir.  Dog  Ridge  has  ripened  fruit  on  its 
cion  varieties  2  days  ahead  and  13  days  after  the  same  varieties  on  Lenoir. 

Table  2. — Ripening  Dates  of  Grape  Varieties  on  Different  Stocks 
{After  Husmanrfi^) 


Stock 

Variety 

Dog  Ridge 

Lenoir 

Rupestris  St. 
George 

Aramon     

Sept.  29 

Sept.  27 
Sept.  20 
Sept.  28 
Sept.  23 
Sept.  10 
Sept.  15 
Sept.  28 

Sept.  28 

Bastardo 

Sept.  23 
Sept.  28 
Sept.  23 
Sept.  23 
Sept.  28 
Sept.  26 

Sept.  25 
Sept.  26 

Bicane 

Blauer  Portucieser 

Sept.  24 
Sept.  15 

Boal  de  Maderc     

Sept.  24 

Sept.  24 

Data  introduced  later  to  show  differences  in  the  composition  of  fruit 
on  several  stocks  may  be  anticipated  here.  Those  differences  that  are 
found  can  be  considered  to  represent  such  as  might  occur  in  separate 
specimens  on  the  same  tree  or  vine.  Much  of  the  available  data  is  from 
European  sources,  or,  if  from  America,  it  concerns  such  plants  as  are 


564  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

shown  elsewhere  to  be  rather  sensitive  to  temperature  conditions  during 
the  growing  season.  In  other  words,  nearly  all  the  available  data  con- 
cern plants  or  situations  such  that  the  difference  between  heat  required 
and  heat  available  is  small.  The  grape  in  the  northeastern  states  is 
near  the  limit  of  its  summer  heat  requirements;  the  pear  and  the  apple 
are  not. 

The  evident  readiness  of  European  authorities  to  recognize  small 
differences  in  ripening  according  to  the  stocks  used  and  the  preponderance 
of  American  opinion — aside  from  a  few  instances — to  the  contrary  can  be 
reconciled  if  the  climatic  differences  are  considered.  Just  as  a  few  days  of 
unusual  heat  in  the  spring  will  force  into  simultaneous  bloom  varieties 
that  blossom  at  different  times  in  a  cooler  season,  the  greater  heat  at 
harvest  in  America  probably  obscures  small  differences  that  would  be 
apparent  in  a  cool  region  or  in  a  cool  season. 

End-season  Effects.  Maturity  of  Wood. — Evidence  of  the  effect  of  the 
stock  on  the  maturity  of  the  wood,  on  the  contrary,  seems  brought  out 
more  clearly  in  America  than  in  Europe  because  of  the  different  winter 
climates  and  the  intimate  relation  of  maturity  to  hardiness.  There  is, 
however,  some  mention  of  these  effects  in  parts  of  France.  Baco  reports 
considerable  difference  in  the  time  of  ripening  of  the  wood  in  grapes, 
stating:  "In  recapitulation,  the  grafted  vines  ripened  their  canes  less 
than  vines  on  their  own  roots.  In  this  respect  many  grafts  have  appeared 
to  us  to  be  influenced  by  the  stock  about  as  they  would  be  by  nitrogen- 
ous fertilizers  or  by  a  mellow  deep  and  fertile  soil  if  one  had  not  grafted 
them,"*  Since  these  differences  have  most  intimate  relation  to  hardiness, 
they  are  discussed  under  the  effects  of  the  stock  on  hardiness. 

The  fall  of  leaves  from  a  deciduous  stock  does  not  cause  the  fall  of 
leaves  on  an  evergreen  cion.  Though  the  trifoliate  orange  is  deciduous, 
other  varieties  worked  on  it  are  not;  though  the  quince  is  deciduous,  a 
grafted  loquat  top  is  evergreen.  This  holds  true  in  other  cases.  How- 
ever, despite  this  retention  of  foliage,  it  is  probable  that  the  deciduous 
stock  has  some  effect  tending  toward  a  partial  dormancy.  Evidence  of 
this  lies  in  the  smaller  injury  at  a  given  temperature  to  orange  on  trifoliate 
than  on  evergreen  stocks  and  in  the  possibility  of  transplanting  the 
loquat  on  quince  without  "balling"  of  the  roots,  provided  the  leaves  are 
stripped,  though  this  cannot  be  done  if  it  is  on  its  own  roots. 

Spring  Effects. — Returning,  for  the  sake  of  completeness,  to  the  effect 
of  stock  on  spring  growth,  the  behavior  of  cherries  on  Chicksaw  plum 
may  be  cited  as  typical.  The  stock  starts  much  earlier  and  throws  out 
leaves  and  shoots  while  the  cherry  grafts  remain  dormant  until  their 
customary  season  of  growth.  "^^  However,  Brown^^  recognizes  a  delay 
in  blossoming  of  plums  and  almonds  on  certain  varieties  of  plums.  He 
states:  "Blossoms  appear  on  plums  from  1  to  2  weeeks  later  than  the 
almond.     Where  the  plum  stock  has  been  tried  the  delay  has  been  about 


THE  RECIPROCAL  INFLUENCES  OF  STOCK  AND  CION  565 

one-half  the  difference  between  the  two  blooming  periods."  It  seems 
quite  possible  that  this  difference  can  exist  in  one  climate  and  not  in 
another.  A  retarded  entrance  into  the  rest  period  in  the  autmnn  is 
shown  elsewhere  to  delay  the  opening  of  peach  blossoms  in  the  spring.  If 
the  plum  stock  prolongs  growth  in  the  fall,  it  will  evidently  have  a  re- 
tarding effect  on  blossoming  in  the  spring.  However,  the  rest  period  is  a 
retarding  factor  only  in  climates  with  mild  winters  and  early  springs  and 
it  is  only  in  such  climates  that  the  retarding  influence  of  plum  stocks  would 
become  obvious.  In  the  north  the  rest  period  ends  before  the  dormant 
period  and  no  retarding  influence  from  the  stock  would  be  expected. 

Baco^  recorded  considerably  more  copious  bleeding  in  Baroque  and 
Tannat  grapes  grafted  on  various  American  and  hybrid  stocks  than  on 
their  own  roots.  He  also  reported  differences  in  the  time  of  breaking  of 
the  buds ;  those  on  the  own-rooted  vines  opened  much  more  regularly  and 
somewhat  earlier  than  those  on  the  grafted  vines.  As  a  rule  the  vines 
on  hybrid  stocks  blossomed  later  and  more  irregularly. ■■* 

Here  again,  as  in  the  ripening  of  fruits,  it  is  in  Europe  and  particularly 
with  grapes  that  more  attention  is  given  to  slight  differences  due  to  stocks 
and  here  again  climatic  factors  explain  the  few  differences  observed. 

Several  European  commentators  are  inchned  to  emphasize  the  need 
of  substantially  the  same  seasons  of  growth  inception  in  stock  and  cion 
to  insure  compatibihty.  Lindemuth  states  that  his  investigations  have 
led  him  to  the  same  conclusion  in  this  respect  as  that  of  Lucas,  to  wit :  a 
graft  of  an  early  starting  kind  on  a  late  starting  kind  is  never  successful: 
"  .  .  .  late  starting  kinds  grafted  on  early  starting  stocks,  very  fre- 
quently become  sick,  since  they  are  not  able  to  take  up  the  quantity  of 
sap  which  the  early-starting  seedling  offers.  Canker  injuries  at  the  point 
of  grafting  are  very  often  the  consequences  of  defective  grafts  of  this 
kind.  Less  easily  does  the  early  starting  cion  become  sick  on  late  starting 
sorts.  The  more  nearly  equal  in  time  and  strength  the  growth  of  the 
cion  and  stock  are,  the  better,  according  to  the  opinion  of  Dr.  Lucas,  is 
the  success  of  the  graft." ^''- 

An  expression  of  the  same  influence  in  the  apple  in  Brittany  is  fur- 
nished by  Duplessix;^^  "...  if  one  inserts  a  cion  of  Doux  Normandie 
[blossoming  in  June]  on  a  stock  from  seed  of  Launette  [blossoming  late 
in  April],  the  sap  will  ascend  in  the  trunk  6  weeks  before  the  graft  is 
ready  to  receive  it.  The  tree  may  die.  If  it  lives  the  sap  will  accumulate 
in  the  swelling  at  the  base  of  the  graft  and  this  swelling  .  .  .  can 
become  in  its  turn  a  cause  of  death.  ...  If  the  reverse  be  tried,  the 
cion  of  Launette  will  require  sap  when  the  Doux  Normandie  trunk  is 
not  ready  to  provide  it  and  the  cion  of  Launette  will  perish  or  it  will  grow 
slowly  for  want  of  feeding  at  a  useful  time. 

"...  A  stock  starting  earlier  than  the  graft  is  preferable  to  one 
starting  later." 


566  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Though  these  two  views  differ  in  details,  they  agree  in  the  general 
harmfulness  of  great  differences  in  the  starting  season  between  stock  and 
cion.  The  very  fact  that  these  differences  can  become  harmful  is  evi- 
dence against  any  considerable  modification  of  either  stock  or  cion  in 
season  of  growth  inception. 

In  brief,  then,  the  influence  of  the  stock  on  the  season  of  the  cion  may 
be  stated,  for  spring  manifestations,  in  Knight's  words:  "The  graft,  or 
bud,  whenever  it  has  become  firmly  united  to  the  stock,  wholly  regulates 
the  season  and  temperature,  in  which  the  sap  is  to  be  put  in  motion,  in 
perfect  independence  of  the  habits  of  the  stock,  whether  these  be  late 
or  early."  Concerning  the  effects  on  autumnal  processes,  it  may  be  said 
that  some  influences  exist  but  may  be  obscured  by  the  climate  and  that 
they  are  not  necessarily  parallel  to  the  nature  of  the  stock. 

Hardiness. — As  to  the  effects  of  the  stock  on  the  hardiness  of  the  cion 
there  is  considerable  conflict  of  evidence,  due  in  part,  perhaps,  to  lack 
of  precise  definitions.  It  is  frequently  stated  in  European  pomological 
literature  that  pears  on  quince  stock  are  much  freer  from  canker  than  on 
pear  stock.  Elsewhere  in  this  work  rather  strong  evidence  is  cited  to 
show  that  the  common  frost  canker  of  Europe  is  associated  with  lack  of 
maturity.  Evidence  presented  earlier  in  this  section  suggests  that  cer- 
tain stocks  may  affect  the  season  of  maturity  of  the  tops. 

Hardiness  has  been  shown  to  be  involved  to  a  great  extent  with  water- 
retaining  capacity  which  in  turn  appears  to  depend  in  no  little  degree  on 
maturity.  It  may  be  affected  by  cultural  practices  and  in  some  cases, 
apparently,  by  the  stocks  used.  The  stock  may,  to  this  extent,  be  con- 
sidered to  induce  hardiness  in  the  top.  If,  however,  the  conception  of 
hardiness  be  that  of  a  specific  property  which  is  present  or  absent  there 
is  no  evidence  that  it  is  transmitted  from  stock  to  cion.  It  is  conceivable 
that  a  stock  may  in  itself  be  hardy  but  through  the  congeniality  of  the 
graft  it  may  actually  diminish  the  hardiness  of  the  cion. 

Fruit  growers  of  the  upper  Mississippi  Valley  have  a  well  defined 
belief  that  such  varieties  as  Jonathan  and  Grimes  are  rendered  hardier 
by  topworking  on  Haas,  Oldenburg  and  similar  hardy  varieties.  It 
seems  plausible  that  with  some  varieties  there  is  a  certain  increase  in 
hardiness  due  to  a  slightly  earlier  maturity;  more  important,  however, 
is  the  consideration  that  the  cases  under  examination  are  not  so  much 
cases  of  increasing  hardiness  as  they  are  of  substituting  a  hardy  variety 
in  those  parts  of  the  tree  that  are  particularly  susceptible  to  winter  injury. 
Even  though  the  hardiness  of  the  cion  were  not  increased  in  the  least,  a 
tree  of  Jonathan  topworked  into  Oldenburg  framework  could  not  help 
but  be  hardier,  though  only  within  limits.  Macoun,^''^  in  Canada,  top- 
working  such  varieties  as  Baldwin  into  hardy  stocks,  was  unable  to 
increase  the  hardiness  sufficiently  to  stand  a  test  winter. 

Hedrick^^  reports  that  Mahaleb  stock  makes  hardier  tops  in  cherries, 


rUE  RECIPROCAL  INFLUENCES  OF  STOCK  AND  CION  567 

both  in  nursery  and  in  orchard,  because  of  the  earher  ripening  of  the  wood. 
Prunus  lusitanica  is  said  to  ripen  its  wood  earher  on  Prunus  Padus  stock 
than  on  its  own  roots  and  to  withstand  cold  weather  better,  probably 
on  that  account.^"*  Budd^^  reports  the  Jonathan  apple  ripening  its 
terminal  shoots  better  on  Gros  Pomniier  "than  on  its  own  roots"  and 
states  that  "the  hardiness  of  a  variety  is  increased  by  the  influence  of  a 
stock  with  a  determinate  habit  of  growth.  ...  In  our  own  State 
[Iowa]  we  have  evidence  that  by  the  selection  of  proper  stock  we  can 
grow  Jonathan  or  Dominie  on  low,  wet  soils  where  they  would  not  reach 
bearing  size,  root-grafted  .  .  .  the  main  utility  with  us  of  top-working 
on  such  prepotent  stocks  as  Gros  Pomier,  Duchess,  Wealthy,  Wolf  River, 
etc.,  is  in  the  way  of  fitting  the  less  hardy  scion  for  enduring  the  tempera- 
ture of  our  test  winters." 

Experience  with  grafted  grapes  in  regions  where  winter  killing  is 
important  was  more  extensive  in  an  earlier  generation  than  in  the  present. 
The  literature  of  the  times  shows  a  tendency  to  agreement  in  the  increased 
hardiness  of  certain  varieties  such  as  lona  and  Adirondac  on  hardy  stocks 
such  as  Concord.  Precise  observations  as  to  the  reason  for  this  were 
not  common,  but  the  suggestion  was  made  that  lona  roots  were  tender."^ 
The  increased  hardiness  was  secured,  if  this  be  true,  by  the  substitution 
of  a  hardy  variety  in  a  tender  part  and  not  by  changing  the  nature  of  the 
cion.  Here  again,  roots  inducing  early  maturity  appear  to  increase 
hardiness.  Nicholas  Longworth,^^  after  extensive  trials,  reported, 
"Foreign  vines  grafted  on  our  natives  are  equally  tender  as  on  their  own 
stock  and  are,  with  me,  often  killed  down  to  the  native  stock." 

It  is  not,  it  should  be  noted,  invariably  the  stocks  inducing  early 
maturity  that  are  hardiest.  St.  George  stocks,  as  reported  by  Hedrick, 
induced  late  growing  in  many  cases;  however,  they  suffered  rather  less 
from  winter  killing  than  the  other  stocks  tested.  Hedrick  suggested  that 
the  deep  rooting  habit  of  this  variety  may  be  connected  with  its  hardiness. 

Onderdonk^i^  and  Vosbury^*^  reported  that  in  the  Gulf  States  the 
trifoliate  orange  increased  the  hardiness  of  the  varieties  worked  upon  it 
and  attributed  the  hardiness  to  the  deciduous  habit  of  the  trifoliate, 
inducing  a  degree  of  dormancy  in  the  cion  varieties  and  thereby  making 
them  more  cold  resistant.  In  the  freeze  of  1913  in  Cahfornia  lemons 
worked  on  orange  trunks  proved  more  hardy  than  those  on  their  own 
trunks,  hardier  not  only  in  the  orange  trunks  but  in  the  lemon  tops.  It 
was  suggested  ^^^  that  in  some  way  the  trunks  of  the  trees  modified  the  dor- 
mancy of  the  tops.  This  condition  was  more  apparent  in  young  trees 
than  in  those  of  bearing  age.  As  in  the  Gulf  States,  trees  on  trifoliate 
were  somewhat  hardier  than  those  on  other  stocks.  In  cases  of  severe 
injury,  however,  when  the  entire  top  has  been  killed,  the  trifohate 
is  unable  to  send  up  any  sprouts  and  dies,  though  it  has  not  itself  suffered 
any  direct  injury  from  the  cold  weather. 


568  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Disease  Resistance. — Cole'*''  recommends  the  "Kentish  sucker  as  a 
cherry  stock  for  fruit  growers  in  Victoria  because  many  varieties  are 
less  likely  to  gum  when  worked  upon  this  stock  than  on  Mazzard  seed- 
lings." Presumably  the  gumming  to  which  Cole  refers  is  the  physiologi- 
cal type.  Barss,^*  in  Oregon,  recommends  the  genuine  Mazzard  stock 
as  freer  from  bacterial  gumming  than  miscellaneous  seedlings  from  the 
ordinary  sweet  varieties.  This,  however,  is  another  case  of  substitution 
in  part  of  the  tree  rather  than  of  change  in  the  part  grafted  in,  since  to 
secure  the  greater  freedom  from  the  disease  it  is  necessary  to  grow  the 
tree  two  or  three  seasons  in  the  nursery  or  the  orchard  and  then  graft 
it  over  in  the  limbs. 

Sometimes  increased  resistance  to  fungous  diseases  is  claimed  from 
top  working,  as  in  the  gooseberry  on  Ribes  aureum,  but  no  evidence  is 
available  of  any  direct  influence.  In  the  case  just  cited  any  increased 
resistance  is  due  probably  to  the  changed  habit  of  the  plant,  the  increased 
height  securing  better  aeration. 

In  California  the  black  walnut  is  used  as  a  stock  for  the  English 
walnut  {Juglans  regia),  in  large  part  because  of  its  resistance  to  a  soil 
fungus,  the  mushroom  root  rot  {Armillaria  mellea),  to  which  the  English 
walnut  roots  are  very  susceptible.  This  is,  again,  a  case  of  substitution 
and  not  an  influence  of  stock  on  cion. 

The  claim  is  sometimes  made  that  certain  stocks  make  the  top  more 
or  less  resistant  to  insect  or  fungous  attack.  Since  vigorously  growing 
trees  are  more  subject  to  aphis  or  to  fire  blight  and  perhaps  less  subject 
to  certain  cankers,  it  is  quite  conceivable  that  a  stock  affecting  growth 
may  indirectly  have  such  an  influence.  The  same  effect,  however,  can 
be  secured  by  cultvu^al  practice  and  no  available  evidence  indicates 
any  modification  of  a  specific  nature  in  the  cion  by  the  stock  making  it 
more  or  less  liable  to  insect  or  fungus  attack. 

Physiological  Diseases. — Diseases  of  a  mosaic  nature  are,  of  course, 
transmitted  in  either  direction  by  grafting.  DanieP^  states  that  some 
cases  of  court  noue  in  the  grape  can  be  traced  to  grafting  and  expresses 
the  belief  that  it  is  due  to  "a  kind  of  physiological  trouble  induced  by 
osmotic  changes  caused  by  the  union  of  plants  of  different  chemical 
functional  capacities."  Daniel's  statement  that  the  characteristic 
shortened  internode  appears  also  on  shoots  from  the  stock  suggests  a 
condition  similar  to  the  transmission  of  pathological  variegation  rather 
than  a  specific  change  due  to  grafting.  Daniel  states  that  grafted  beans 
grown  in  nutrient  solution  were  free  from  chlorosis  longer  than  check 
plants  which  had  absorbed  more  of  the  solution.  ''Since  the  chlorosis 
could  not  be  attributed,"  he  states,  "to  anything  but  the  presence  of 
an  excess  of  a  salt  (carbonate  of  lime,  or  another),  it  is  necessary  to 
admit  that  this  salt  has  passed  in  less  quantity  because  of  the  different 
osmosis  and  because  of  its  utilization  at  the  graft-union  to  neutralize  the 


THE  RECIPROCAL  INFLUENCES  OF  STOCK  AND  CION  569 

acidity  of  the  wound  surface.  In  a  word,  these  results  show  very  clearly 
that  the  graft,  considered  by  itself,  modifies  the  regimen  of  water  and 
of  soluble  salts,  that  is  to  say,  of  the  functional  capacities  of  the  grafted 
plants." 

In  support  of  this  view  he  cites  Viala  and  Ravaz  to  the  effect  that  the 
Herbemont  grape  was  free  from  chlorosis  on  Clairette;  likewise  Merlot 
on  Viala.  It  seems  possible  that  these  last  instances  may  be  due  to  a 
high  degree  of  congeniality  between  the  varieties  mentioned.  Blunno^* 
states  that  many  resistant  stocks  are  without  chlorosis  until  they  are 
grafted,  but  become  so  afterward,  explaining  this  through  the  weakening 
of  the  plants  by  grafting.  Susceptibility  is  greater,  he  reports,  when  the 
graft  is  not  well  healed  and  any  weakening  influence  such  as  a  fungus  or 
insect  pest,  even  on  a  resistant  variety,  favors  infestation  by  phylloxera. 

Since  John  Lawrence, ^^  in  1717,  noted  the  transmission  from  the  cion 
to  the  stock  of  variegation  in  leaves,  this  fact  and  its  converse  have  been 
cited  as  standard  evidence  of  the  influence  of  stock  on  cion  or  of  cion  on 
stock  or  both.  Numerous  instances  of  such  transmission  are  easily  found, 
but  have  lost  much  of  their  significance  through  the  view  that  in  many 
cases  variegation  is  a  pathological  condition  and  that  grafting  is  in  such  a 
case  also  an  inoculation.  Variegation  arising  from  other  than  patho- 
logical causes  seems  not  to  be  transmitted  from  stock  to  cion  or  from  cion 
to  stock. 

Yield. — Some  commentators  are  disposed  to  believe  that  grafting 
per  se  disposes  the  plant  to  fruitfulness.  This  is  well  expressed  in  this 
statement:  "Seedling  apples,  especially  those  which  are  of  a  vigorous 
nature,  run  to  wood  and  produce  few  fruits,  or  begin  very  late  to  produce 
them.  Grafted  apples,  on  the  contrary,  begin  earlier  to  fruit." ''^  .  .  . 
Undoubtedly  early  bearing  is  favored  by  grafts  which  have  not  united 
perfectly,  just  as  it  is  by  ringing  or  by  any  influence  obstructing  trans- 
location. Whether  grafts  which  unite  readily  have  the  same  effect  is 
not  so  clear.  Precocity  of  bearing  is  necessary  to  the  success  of  any 
variety  in  cultivation;  deficiency  in  this  respect  is  the  chief  objection 
to  the  Northern  Spy  apple  and  the  chief  reason  that  it  is  now  so  little 
planted.  Naturally,  then,  grafted  trees  of  cultivated  varieties  tend  to 
come  into  bearing  early;  otherwise  the  varieties  would  not  be  in  culti- 
vation. Some  varieties  come  into  bearing  at  an  earlier  age  than  others, 
though  all  are  grafted  presumably  on  the  same  stocks.  This  time  can 
be  hastened  or  retarded  by  cultural  means.  Vigorous  seedlings  are 
late  in  bearing;  so  are  vigorous  grafted  trees.  There  seems  no  clear 
evidence  that  grafting  in  itself,  as  commonly  practiced  in  fruit  trees, 
hastens  the  time  of  bearing. 

The  influence  of  different  stocks  on  the  functioning  of  the  cion  is 
shown  neatly  by  experiments  such  as  those  of  Lindemuth'-**  on  potatoes. 
This  investigator  found  that  the  potato  on  Datura,  a  vigorous  growing 


570  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

stock,  forms  aerial  stolons  freely.  The  combination  plant  grows  vigorously 
and  manufactures  much  starch  which  cannot  go  into  tuber  formation  as 
it  would  in  an  ordinary  potato  plant.  It  is,  therefore,  because  of  the 
vigor  of  the  stock,  utilized  in  the  conversion  of  the  potato  stolons  into 
leafy  shoots.  On  a  weakly  growing  stock,  however,  such  as  Capsicum 
annuum,  starch  accumulation  exceeds  utilization  and  tuber  formation 
ensues  from  the  buds  which  on  Datura  stocks  give  rise  to  shoots. 

Fruit-bud  Formation. — Voechting^^^  "has  shown  that  buds  which  grew 
from  the  base  of  the  inflorescence  of  a  beet  in  the  second  year  came  out  as 
leafy  shoots  supplied  with  large  leaves,  if  they  were  grafted  on  a  1-year 
beet;  on  the  contrary,  they  infloresced  if  they  were  placed  on  a  stock 
already  in  its  second  year." 

Leclerc  du  Sablon^^  shows  differences  in  total  carbohydrates  in 
the  tops  of  Angouleme  2  years  grafted  on  pear  and  on  quince  stocks. 
Except  in  May  the  carbohydrate  content  of  the  pear  on  quince  is  higher 
than  that  of  the  pear  on  pear.  In  view  of  the  importance  of  carbohy- 
drate content  to  fruitfulness  this  difference  seems  of  possible  signifi- 
cance, though  it  is  comparatively  slight  at  the  ordinary  time  of  fruit 
bud  formation. 

Table  3. — Total  Carbohydrates  in  Tops  of  Angouleme  Pears  Grafted  on  Pear 

AND  on  Quince 

(After  Leclerc  du  Sahlon^'^) 

(Per  cent,  on  dry  weight  basis) 

On  Pear  On  Quince 

Jan.     19 23.7  25.9 

Feb.    26 21.7  25.4 

Mar.  28 24.3  27.9 

May   9 21.6  21.3 

June    17 22.2  22.6 

July    22 22.6  22.9 

Sept.  7 24.5  25.8 

Oct.     16 23.4  25.4 

Nov.  22 23.4  25.3 

Dec.    26 23.4  25.5 

Specific  citations  are  hardly  necessary  to  show  the  influence  of 
certain  stocks  on  fruit-bud  formation.  The  dwarfing  stocks,  through 
limiting  growth  and  therefore  carbohydrate  utilization,  have  a  general 
tendency  to  permit  sufficient  carbohydrate  accumulation  for  free  forma- 
tion of  fruit  buds.  European  and  Japanese  chestnuts,  for  example, 
worked  into  chinquapin,  bear  in  1  or  2  years. ^^  It  should  be  remem- 
bered, however,  that  the  total  framework  on  which  fruit  buds  can  be 
formed  is  smaller  and  the  total  production  of  fruit  buds  on  a  given  area 
of  ground  is  not  necessarily  greater  and  may  even  be  smaller,  when 
dwarfing  stocks  are  used.  In  some  cases  certain  stocks  not  dwarfing 
in  themselves  make  poor  unions  with  cions  set  in  them  and  exercise  a 


THE  RECIPROCAL  INFLUENCES  OF  STOCK  AND  CI  ON 


571 


dwarfing  effect.  Some  Wildgoose  plums  are  said  to  be  more  fruitful 
on  peach  roots. '^'* 

These  instances  are  introduced  here,  not  as  showing  a  general  tend- 
ency toward  any  marked  influence  of  stock  on  cion,  but  rather  the 
dearth  of  more  positive  evidence.  Considering  the  amount  of  top- 
working  that  has  been  done,  little  evidence  of  a  change  of  practical  im- 
portance has  been  accumulated.  There  has  been  a  general  tendency 
to  assume  that  if  there  is  any  influence  on  the  size  of  fruit  the  dwarfing 
stocks  tend  to  produce  larger  fruit.  Most  of  the  instances  just  cited 
fail  to  bear  out  this  idea. 

In  Victoria  Cole"*"  reports  that  many  varieties  of  plums  which  are 
shy  bearers  on  Myrobalan  stock  are  prolific  on  Marianna.  "Although 
some  varieties  .  .  .  somewhat  overgrow  this  stock  it  is  no  great  fault 
but  an  improvement — it  influences  the  bearing  qualities  of  varieties  so 
inclined  to  overgrow." 

In  France  some  years  ago,  according  to  Pepin, ^''^  there  was  a  dwarf- 
ing apple  stock,  neither  Paradise  nor  Doucin,  known  as  the  Pommier 
hybride  or  batard;  grafts  on  this  grew  vigorously  but  bore  little  fruit 
and  that  little  was  inferior. 

Bioletti,^^  reporting  on  the  St.  George  grape  stock,  states:  "In  some 
cases  the  vines  grow  well  but  the  crops  are  unsatisfactory.     This  has 

Table  4. — Product  of  Panariti  Grapes  on  Different  Stocks  at  Fresno,  Cal. 
{After  Husmann^*) 


Stock 


Yield  (in  pounds 
per  vine) 


1917 


1918 


Sugar  content 
(Balling  scale) 


1917 


1918 


Acid  as  tartaric 

(grams  per  100 

cubic  centimeters) 


1917 


1918 


Adobe  Giant 

Aramon  X  Rupestris  Gan- 

zin  No.  1 

Dog  Ridge 

Lenoir 

Mourvedre     X    Rupestris 

No.  1202 

Riparia  Gloire 

Riparia  X  Rupestris     No. 

3309 

Rupestris  St.  George 

Salt  Creek 

Solonis     X     Riparia    No. 

1616 

Average 


21.0 
3.0 
1.5 

8.0 
5.0 

17.0 
6.5 
8.0 

24.5 

10.2 


7.5 

11.0 
3.0 
2  0 

1.5 
2.0 

20.0 
2,0 
1.5 

19.0 

6.95 


30.5 

28.0 
26.5 
28,0 

23.5 
23.5 

28.5 
28.5 
28,0 

29.0 

27.4 


27.0 

26,0 
28.0 
26.0 

28.0 
30.0 

26.0 
26.0 
26,0 

26.0 

26.9 


0.9675 

0.7650 
0.8300 
0.6450 

0.8700 
0.8850 

0.8650 
0.7800 
0.7800 

0.6900 

0.80775 


0.8770 

0.8255 
0.8250 
0.7500 

0.7575 
0.9450 

0.8250 
0.8550 
0.8175 

0.8325 


0.8310 


572  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

been  noted  only  in  rich  valley  soil  of  the  coast  counties  and  only  with 
certain  varieties.  A  similar  condition  has  often  been  noted  in  Europe, 
but  it  is  usually  easily  overcome  by  longer  pruning  and  diminishes  with 
age. " 

Husmann^^  shows  very  striking  differences  in  the  product  of  the 
Panariti  or  currant  grape  on  various  stocks  in  California,  as  shown  in 
Table  4. 

Rolfs^-^  suggests  a  difference  in  the  value  of  different  stocks  for  the 
mango.  The  kumquat  on  sour  orange  roots  grows  a  vigorous  tree  but 
it  is  practically  barren. 

Fruit  Setting. — A  casual  survey  of  European  literature  shows  a  con- 
siderable body  of  opinion  to  the  effect  that  the  setting  of  fruit  is  influenced 
sometimes  by  the  stock  on  which  the  fruiting  wood  is  worked.  Par- 
ticularly does  this  appear  in  grapes.  Ravaz  is  quoted  to  the  effect  that  in 
sandy  soils  strong  growing  stocks  fail  to  set  fruit  and  for  this  reason  many 
of  the  Riparia  and  Rupestris  hybrids  are  not  well  suited  to  such  soils. ^*^ 
Baco^  found  the  short  and  reflexed  stamens  characteristic  of  many  hybrid 
stocks,  but  very  rare  in  the  pure  Vinifera,  produced  in  Baroque  grafted  on 
1202.  These  characters  have  been  shown  in  the  section  on  Fruit  Setting 
to  be  associated  with  lack  of  viability  in  the  pollen.  Though  it  is  not 
clear  from  Baco's  account  whether  this  condition  was  universal  on  this 
stock,  he  recorded  it  on  other  stocks  also,  including  the  Rupestris  du  Lot 
(St.  George).  Consequent  upon  this  condition  was  a  considerable 
amount  of  couture  and  of  miller andage.  Nevertheless,  he  recorded  a 
general  increase  in  production  on  these  same  stocks.*^ 

Rupestris  du  Lot  stock  is  reported  to  cause  poor  setting  of  fruit  in 
many  Victorian  vineyards  ;^^  the  vigorous  growth  of  this  same  stock 
produces  coulure  in  some  varieties  in  California.  ^^^  Odart,  writing  before 
the  days  of  phylloxera  in  Europe,  stated  that  the  Raisin  des  Dames  set 
fruit  much  better  when  grafted  on  the  common  white  Muscat;''^  Bur- 
bidge^^  cites  similar  cases  from  the  experience  of  forcing  house  grape 
growers.  Baltet'^  states  that  the  Cabernet  grape  when  grafted  is  exempt 
from  coulure  beside  own-rooted  plants  that  are  badly  affected  and  quotes 
Hardy:  "Graft  the  Chasselas  Gros-Coulard,  even  on  itself,  and  you  will  be 
resisting  coulure."  In  Australia  when  the  Kieffer  pear  is  grown  on  wet 
soils  better  setting  occurs  if  quince  roots  are  used."*^  Sahut'^"  states  that 
Chionanthus  virginica,  grafted  on  ash,  flowers  abundantly  but  never 
fruits,  while  as  a  seedling  it  bears. 

Size  of  Fruit. — So  many  factors  affect  the  size  of  fruit  that  it  is  difficult 
to  find  clear  evidence  of  any  considerable  influence  on  size  that  can  be 
attributed  to  the  stock.  Sometimes  grape  growers  imagine  an  increase 
in  the  size  of  the  individual  berries  when  certain  stocks  are  used.  Bur- 
bidge,'^  for  example,  cited  an  instance  in  which  the  Gross  Guillaume  grape 
was  considered  to  form  larger  berries  on  Muscat  of  Alexandria  than 


THE  RECIPROCAL  INFLUENCES  OF  STOCK  AND  CION 


573 


on  Black  Hamburg.  Pepin '^'^  stated  that  certain  almonds  grafted  on 
bitter  almond  or  on  St.  Jiilien  plum  stocks  bore  smaller  fruit.  His 
statement  of  a  stock  which  produced  small  fruit  in  the  apple  has  been 
mentioned  earlier.  Daniel^^  found  that  tomato  grafts  on  pimento  pro- 
duced less  fruit  than  on  their  own  roots  and  that  the  fruit  was  generally 
smaller.  The  Golden  Pippin  in  England  when  worked  on  free  growing 
stock  was  said  to  l)c  larger,  mealy  and  poorer  in  keeping  quality  than 
on  less  vigorous  stock.  "^^  In  America  some  of  the  older  generation  of 
pear  growers  thought  that  small  fruited  varieties,  such  as  Dana's  Hovey, 
bore  larger  fruits  when  worked  on  vigorously  growing  stocks.  The  sand 
cherry  has  been  said  to  produce  larger  fruits  on  Prunus  americana  than 
on  its  own  roots."^  IVIany  California  growers  believe  that  peach  roots 
induce  larger  fruit  in  both  European  and  Japanese  plums  than  plum  or 
almond  roots.  ^^^  Hedrick,''^  however,  reported  no  difference  in  numerous 
varieties  of  apples  grown  on  Doucin,  Paradise  and  standard  stocks. 

Reference  has  been  made  to  the  greater  growth  of  American  grapes 
on  certain  stocks  in  an  experimental  planting  in  New  York.''^  The  same 
investigation  showed  much  greater  productivity  in  the  grafted  vines. 
Typical  comparisons  are  shown  in  Table  5,  condensed  from  Hedrick's 
results.  Summarizing,  on  an  acre-yield  basis,  the  results  for  all  varieties, 
including  many  not  listed  in  the  table  just  given,  the  yields  by  stocks  for 
that  year  were,  in  tons  per  acre:  on  own  roots,  4.39;  on  St.  George, 
5.36;  on  Gloire,  5.32  and  on  Clevener,  5.62.  Averages  for  3  years  were  in 
the  same  order  of  magnitude. 

Table  5. — Average  Yield  per  Vine  of  Own  Root  and  Grafted  Grape  Varieties, 

1911 

(After  Hedrick-'^) 


Variety 


Ovvn  roots, 
pounds 


St.  George, 
pounds 


Gloire, 
pounds 


Clevener, 
pounds 


Campbell . 
Concord. . 
Vergennes 
Herbert. . 

lona 

Niagara . . 
Catawba . . 
Delaware . 
Brighton . , 
Worden . . 


16.00 
16.20 
17.36 
12.21 
15.17 
20.51 
15.37 
12.75 
14.43 
10.37 


23.69 
16.93 
22.13 
11.89 
16.42 
22.55 
12.95 
24.25 
15.56 
16.47 


20.41 
16.95 
24.52 
14.95 
17.68 
24.57 
16.41 
14.25 
13.06 
15.95 


18.35 
21.17 


21.79 
21.94 
17.75 
17.40 
15.71 


"The  crop  on  the  grafted  vines  was  increased,"  Hedrick  states, 
"through  the  setting  of  more  bunches  and  the  growth  of  larger  bunches 
and  berries.     The  increase  in  the  number  of  bunches  was  easily  deter- 


574  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

mined  by  actual  count  but  for  the  statement  regarding  size  we  have  only 
the  fact  that  the  proportion  of  unmarketable  grapes  was  greater  on  the 
ungrafted  than  on  the  topworked  vines.  The  greater  fertility  of  the 
varieties  on  other  than  their  own  roots  cannot  be  ascribed  to  larger  vines. 
No  data  are  available  as  to  size  of  vines  but  judging  by  the  eye  alone  the 
grafted  vines  do  not  make  as  much  wood  as  do  the  varieties  on  their  own 
roots." 

It  should  be  stated  that  there  is  by  no  means  a  unanimity  of  opinion 
as  to  the  effect  of  dwarfing  stocks  on  the  size  of  the  individual  fruit,  even 
in  Europe. 

Quality. — Practically  all  the  older  authorities  were  agreed  that  in 
some  cases  the  stock  influences  the  quality  of  the  fruit  borne  by  the  cion; 
as  to  the  extent  of  this  influence  there  was  more  diversity  of  opinion. 

Downing,^"  writing  in  1845,  stated:  "A  slight  effect  is  sometimes  produced 
by  the  stock  on  the  quality  of  the  fruit.  A  few  sorts  of  pear  are  superior  in 
flavour  but  many  are  also  inferiour,  when  grafted  on  the  Quince,  while  they  are 
more  gritty  on  the  thorn.  The  Green  Gage,  a  plum  of  great  delicacy  of  flavour 
varies  considerably  upon  different  stocks;  and  Apples  raised  on  the  crab,  and 
Pears  on  the  Mountain  Ash,  are  said  to  keep  longer  than  when  grown  on  their 
own  roots." 

Barry^^  spoke  of  the  Beurre  Diel  pear  as,  "Sometimes  gritty  at  the  core  on 
pear  stock;  invariably  first  rate  on  the  quince."  Again,  of  the  Glout  Morceau: 
"like  the  Duchesse  d'Angouleme,  Louise  Bonne  and  some  others,  it  is  decidedly 
superior  on  the  quince."^* 

Lindley^^  wrote:  "It  is  not  merely  upon  the  productiveness  or  vigour  of  the 
scion  that  the  stock  exercises  an  influence;  its  effects  have  been  found  to  extend 
to  the  quality  of  the  fruit.  This  may  be  conceived  to  happen  in  two  ways — 
either  by  the  ascending  sap  carrying  up  with  it  into  the  scion  a  part  of  the  secre- 
tions of  the  stock,  or  by  the  difference  induced  in  the  general  health  of  a  scion  by 
the  manner  in  which  the  flow  of  ascending  and  descending  sap  is  promoted  or 
retarded  by  the  stock.  In  the  Pear,  the  fruit  becomes  higher  coloured  and  smaller 
on  the  Quince  stock  than  on  the  wild  Pear,  still  more  so  on  the  Medlar.  .  .  . 
Mr.  Knight  mentions  such  differences  in  the  quality  of  his  Peaches.  .  .  .  Since 
the  quality  of  fruit  is  thus  affected  by  the  stock,  it  seems  allowable  to  infer  that 
the  goodness  of  cultivated  fruits  is  deteriorated  by  their  being  uniformly  worked 
upon  stocks  whose  fruit  is  worthless;  for  example,  the  Almond  or  the  austere 
Plum  can  only  injure  the  Peaches  they  are  made  to  bear,  the  Crab  the  Apple, 
and  so  on."  Lindley  cites  with  apparent  approval  numerous  other  instances 
of  the  sort. 

A  generation  later  the  grape  growers  of  France  were  forced  by  the 
ravages  of  the  phylloxera  to  confront  this  question  in  connection  with  the 
grafting  of  their  Vinifera  varieties  on  American  vines  whose  fruit  was, 
at  the  best,  of  indifferent  quahty.  Much  misgiving  was  felt  lest  the 
quality  of  the  wines  made  from  the  new  combination  plants  should  be 
inferior  to  that  of  the  older  vines  on  their  own  roots.     This  great  experi- 


THE  RECIPROCAL  INFLUENCES  OF  STOCK  AND  CION         575 

ment,  one  of  the  greatest  pomological  experiments  the  world  has  seen, 
has  failed  to  show  any  consistent  deterioration  in  the  quality  of  the  prod- 
uct that  could  be  attributed  to  the  use  of  American  stocks.  In  fact,  at 
times  wine  from  grafted  vines  has  brought  higher  prices  than  that  from 
the  same  varieties  on  their  own  roots.  >^ 

Sahut  cites  among  instances  where  the  quality  is  not  injured  by  the  stock, 
Vinifera  grapes  on  American  stocks,  cherry  on  Mahaleb,  almond  on  bitter  almond, 
apricot  on  the  common  plum.  In  some  cases,  he  states,  more,  larger  and  better 
fruits  are  secured  by  particular  stocks,  as  in  pears  on  the  quince,  apples  on  the 
Paradise,  peach  on  the  almond.  The  loquat  on  hawthorn,  he  states,  is  more 
perfumed  and  less  acid  than  on  its  own  or  on  quince  roots,  while  of  pears  on  haw- 
thorn some  retain  and  some  lose  their  quality. 

Some  years  ago  California  citrus  growers  hesitated  to  use  sour  orange 
stock  through  fear  of  spoiling  the  quality  of  their  fruit,  but  extensive 
tests  have  shown  no  differences  induced  by  either  sour  or  sweet  stock.  ^^° 

Swingle^^''  reports  that  the  Satsuma  orange  on  sweet  orange  stock 
bears  fruit  that  is  coarse,  dry  and  insipid,  as  well  as  being  later  in  ripening 
than  on  trifoliate  stock,  while  on  the  latter  the  fruit  is  much  improved  in 
quality.  Elsewhere  the  incompatibility  between  this  orange  and  all 
stocks  except  trifoliate  is  discussed. 

In  Pomaceous  Fruits. — Riviere  and  Bailhache^^^  present  3  years' 
average  analyses  of  Triomphe  de  Jodoigne  pears  from  trees  of  equal  age, 
standing  side  by  side,  one  on  quince,  the  other  on  pear  roots.  The 
fruits  on  the  standard  tree  averaged  280  grams  in  weight,  those  on  the 
dwarf,  406  grams;  total  sugars  per  liter  of  juice:  in  the  standard,  93.4 
grams,  in  the  dwarf,  102.3  grams.  The  investigators  calculate  that  a 
crop  of  300  fruits  would  produce  on  the  standard  tree  7  kilograms  of 
sugar  and  on  the  dwarf,  11.  Two  years'  investigations  on  Doyenne 
d'hiver  showed:  On  quince  stocks,  average  weight  of  fruit,  435  grams, 
sugar  percentage  in  juice,  11.59;  on  standard,  average  weight  of  fruit, 
230  grams,  sugar  percentage  in  juice,  9.04. 

Commenting  on  some  experimental  tests  of  dwarf  apples  in  New 
York,  Hedrick^'^  states:  "It  is  a  common  claim  that  dwarf  apple  trees 
produce  larger,  handsomer  and  better  flavored  fruits  than  standard  trees. 
There  is  little  in  these  three  orchards  to  substantiate  these  claims.  There 
are  differences  between  trees  on  the  three  stocks  but  they  are  as  often  as 
not  in  favor  of  standards  as  of  dwarfs." 

In  Stone  Fruits. — For  the  stone  fruits  Knight ^°  may  be  quoted: 
"But  I  have  subsequently  planted  two  trees  (of  Moorpark  apricot) 
growing  upon  plum  stocks,  and  two  upon  apricot  stocks,  upon  the  same 
aspects,  and  in  a  similar  soil,  giving  those  upon  the  plum  stocks  the  advan- 
tage of  some  superiority  in  age,  and  I  have  found  the  produce  of  the 
apricot  stocks  to  be  in  every  respect  greatly  the  best.     It  is  much  more 


576 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


succulent  and  melting,  and  differs  so  widely  from  the  fruit  of  the  other  trees 
that  I  have  heard  many  gardeners,  who  were  not  acquainted  with  the 
circumstances  under  which  the  fruit  was  produced,  contend  against  the 
identity  of  the  variety.  The  buds  were,  however,  taken  from  the  same 
tree. 


"I  have  also  some  reasons  for  believing  that  the  quality  of  the  fruit 
of  the  peach  tree  is,  in  some  cases  at  least,  much  deteriorated  by  the  oper- 
ation of  the  plum  stock." 

In  Grapes. — CurteP^  reported  a  difference  in  must  from  Pinot  grapes 
on  their  own  roots  and  on  Riparia  roots.  More  careful  studies  in  1903 
are  recorded  in  Table  6.  In  his  discussion  Curtel  stated  that  there  were 
differences  according  to  the  variety  and  the  stock  and  that  since  the 
amount  of  organic  nitrogen  was  thought  to  explain  the  observed  differ- 
ences in  susceptibility  to  wild  yeasts  the  matter  might  assume  considerable 
practical  importance. 


Table  6. — Analyses  op  Juice  Extracted  from  Grapes 

{After  Curtel*^) 
(Parts  in  1000) 


Pinot 

on 

Riparia 


Pinot 


Gamay 

on 
Solonis 


Gamay 

on 

own  roots 


Dextrose 

Levulose 

Total  acidity 

Bitartrate  of  potassium 

Phosphoric  acid 

Organic  nitrogen 

Ash 

Tannin 

Coloring  matter 


87.30 
102 . 05 
9.20 
8.47 
0.46 
4.02 
5.15 
1.05 
100.00 


81.07 
98.05 
8.54 
8.51 
0.61 
3.17 
5.45 
1.85 
126.00 


153 . 50 


10.43 
9.41 


1.04 
100.00 


158.70 


8.60 
10.43 


1.10 
106.00 


Bioletti  compares  grapes  grown  on  certain  stocks r^^  "The  quahty 
of  the  grapes  was  in  nearly  all  cases,  where  a  comparison  was  possible, 
better  on  Riparia  stock  than  on  St.  George.  The  grapes  were  larger  and 
sweeter.  The  higher  sugar  content  was,  moreover,  usually  accom- 
panied by  higher  acidity,  showing  that  the  grapes  were  better  developed." 
Quantitative  data  are  shown  in  Table  7. 

Husmann^^  uses  sugar  and  acid  determinations  of  grapes  as  a  test  of 
the  congeniality  of  the  graft.  Extensive  determinations  were  made  to 
test  the  effects  of  various  stocks  on  the  quality  of  the  fruit.  "These 
tests,"     Husmann  states,  "have  yielded  very  interesting  and  suggestive 


THE  RECIPROCAL  INFLUENCES  OF  STOCK  AND  CION 


577 


T.\BLE  7. — Comparison  of  Composition  op  Grapes  on  Riparia  and  on  St.  George 

(After  BiolettP^) 


Variety 


Stock 


Riparia  Gloire 


Sugar        Acid 


Riparia      Grande 
Glabre 


Sugar         Acid 


St.  George 


Sugar        Acid 


Valdepenas . . . 

Zinfandel 

Gros  Mansene 

Fresa 

Vernaccia.  .  .  . 
Marsanne.  .  .  . 
Chardonay.  .  . 

Sultana 

Cornichon.  .  . . 

Moan 


27.5 
26.5 
24.1 
25.6 
27.5 
23.3 
25.0 
24.0 


0.65 
0.92 
1.20 
0.92 
0.84 
0.50 
0.60 
0.75 


26.7 
24.0 
27.6 
25.0 

22.8 

20.3 


0.77 


0.80 


24.4 


0.86 


23.5 
24.0 


24.2 
21.6 


22.7 


0.56 
0.85 


0.61 
0.62 


0.75 
0.65 


0.67 


(lata  which,  when  contrasted  with  the  growth  ratings  of  the  same  vines 
based  on  observations  and  measurements  of  growth  during  the  same 
growing  seasons,  indicate  that  there  is  a  close  correspondence  between 
these  important  chemical  constituents  of  the  fruit  and  the  congeniality 
of  graft  and  stock  as  determined  by  observation  of  growth.  Similar  rat- 
ings of  the  growth  of  a  variety  grafted  on  various  stocks  are  found  to  be 
accompanied  by  fairly  definite  percentages  of  sugar  and  acid.  Under 
like  conditions  of  growth  the  sweetness  and  acidity  of  the  fruit,  as  well  as 
its  time  of  ripening,  are  evidently  materially  influenced  by  the  congeni- 
ality of  the  graft  and  stock." 

This  is  of  considerable  importance.  It  indicates  that  the  congeniality 
of  the  graft  is  influential  rather  than  the  stock  and  that  the  same  stock 
may  with  one  variety  increase  the  sugar  content  and  with  another 
decrease  it. 

Qualitative  Differences  and  Quantitative  Variations. — Since  com- 
position, ripening  and  keeping  quality  of  fruits  are  more  or  less  related, 
an  effect  produced  on  one  of  these  implies  an  effect  on  the  others.  It 
was  stated,  many  years  ago,  that  there  was  a  month's  difference  in  the 
keeping  quality  of  Hubbardston  apples  grown  on  Hightop  Sweet  and  on 
Roxbur}'  Russet  in  the  same  soil  and  with  the  same  culture.  Rhode 
Island  Greening  on  Hightop  Sweet  was  said  to  be  only  a  fall  variety.  The 
crab  stock  of  England  made  the  Golden  Pippin  keep  longer  than  did 
the  free  stock.     Daniel,^*  who  states  that  Labrusca  stock  has  a  rather 


578  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

unfavorable   action   on   the   table   and  wine  qualities  of  certain  white 
grapes,  does  not  specify  the  nature  of  the  action. 

These  differences  are  quantitative  rather  than  qualitative.  No 
evidence  is  available  showing  a  qualitative  change  in  fruits,  in  the  sense 
of  an  introduction  or  a  manufacture  of  entirely  different  compounds, 
emanating  from  the  stocks  used.  Furthermore,  accepting  all  the  cases 
alleged,  there  is  still  no  clear  evidence  of  any  change  beyond  such  differ- 
ences as  could  be  effected  by  changes  in  maturity.  A  reference  to  Ravaz 
appears  to  show  a  possible  relation  of  the  stock  to  quality  in  fruit.  It 
is  stated  1^^  that,  "to  secure  high  gravity  must  in  his  opinion  it  is  stocks 
with  Riparia-like  behavior  which  should  be  selected — one  requires  vines 
with  slow  and  regular  vegetation,  the  activity  of  which  ceases  early  in 
the  season.  In  a  word,  the  vines  should  behave  in  as  nearly  as  possible 
the  same  way  as  though  they  were  growing  on  a  dry  hillside." 

Apparently,  then,  the  nature  of  the  fruit  the  stock  bears  is  a  matter 
of  indifference;  the  two  possibly  important  factors  are  (1)  the  vegetative 
habits  of  the  stock,  (2)  the  congeniality  of  stock  and  cion.  In  the  light 
of  present  knowledge  of  the  formation  and  ripening  of  fruit,  it  would  be 
difficult  to  arrive  at  any  other  conclusion.  An  apple  is  sweet  or  sour 
according  as  it  contains  more  or  less  sugar;  the  acid  content  is  fairly 
uniform.  This  is  determined  largely  in  the  spur  or  the  neighboring 
branch;  the  trunk  or  roots  cannot  have  much  effect  on  it.  The  roots 
may  keep  the  tree  growing  late  and  so  influence  the  ripening,  but  the 
quality  of  the  fruit  the  stock  bears  cannot  be  expected  to  influence  the 
top.  A  stock  with  good  fruit  but  unsuitable  vegetative  habits  might 
influence  the  cion  to  produce  inferior  fruit  and  vice  versa;  a  stock  of  a 
sweet  variety  may  make  the  fruit  of  a  cion  sweeter  or  more  acid. 

Longevity. — It  is  the  generally  accepted  view  that  processes  greatly 
increasing  fruitfulness  tend  to  hasten  the  ultimate  death  of  the  plant. 
This  opinion  has  ample  corroboration  in  the  dwarf  apples  and  pears  and 
in  recent  years  has  been  a  very  real  problem  to  grape  growers.  Blunno^^ 
mentions  some  instances  that  have  a  bearing  here. 

"The  Riparias,  which  are  considered  excellent  stocks  for  loose,  rich,  deep 
soils  such  as  are  found  on  river  flats,  have  given  some  disappointment  in  a  few 
places  in  Sicily  and  Algiers,"  he  states.  "For  the  first  few  years  vines  grafted 
on  them  are  loaded  with  fruit,  which  over-production  seems  to  exhaust  the 
plant.   .    .    . 

"Similarly  the  Riparia  X  Rupestris  No.  3306,  which  is  generally  planted  in 
practically  the  same  classes  of  soil  as  the  Riparias  and  the  R  X  R  No.  3309,  in 
soils  a  little  stiff er,  have  gradually  given  signs  of  exhaustion  in  various  localities. 
.  .  .  Wherever  the  Riparia  and  Riparia  X  Rupestris  hybrids  failed  it  was 
always  noticed  that  the  exhaustion  followed  several  years  of  very  heavy  crops; 
those  vignerons  who  managed,  by  a  skilful  pruning,  to  keep  the  vines  from  yield- 
ing so  heavily,  have  these  vines  still  in  bearing." 


THE  RECIPROCAL  INFLUENCES  OF  STOCK  AND  CION  579 

Sometimes  grafting  has  opposite  effects.  Without  specifying  as  to 
the  effect  on  fruitfulness,  Jost  records  that  Pistacia  vera  (the  pistachio 
nut)  as  a  seedUng  Uves  at  the  most  150  years,  on  P.  lentiscus  only  40,  while 
on  P.  terehenthinus  it  reaches  200  years. 

General  Influence  of  Stock  on  Cion. — Such  evidence  as  is  available 
on  the  influence  of  stock  on  cion  has  been  presented.  This  influence 
wherever  it  is  positive,  is,  almost  without  exception,  quantitative.  There 
is  no  doubt  of  the  influence  of  stock  on  vigor  and  form  of  growth;  there 
seems  httle  reason  to  doubt  some  influence  of  the  stock  on  the  termination 
of  the  growing  season,  which  is,  after  all,  only  a  phase  of  vigor.  If,  now, 
the  effect  of  stock  on  vigor  be  accepted,  all  other  influences  of  stock  on 
cion  can  be  explained  through  that  one  influence.  None  of  these  influ- 
ences differs  from  effects  that  might  be  secured  from  so  manipulating 
cultural  conditions  as  to  modify  vigor.  Cultural  conditions  can  be 
changed  to  induce  early  fruiting  or  late  growth  or  earlier  ripening  or 
hardiness  or  disease  resistance  or  increased  fruit-bud  formation  or  better 
setting  of  fruit  or  larger  or  better  ripened  fruits.  Girdling  the  grape 
will  increase  the  sugar  content  and  size  of  the  fruit.  The  dwarfed  trees 
of  China  that  bear  inferior  undeveloped  fruit  are  on  their  own  roots  j^"" 
the  inferiority  of  the  fruit  is  brought  about  by  manipulation,  not  by  any 
influence  of  stock  on  cion. 

The  influence  of  the  stock  on  cion  is  not  to  be  minimized;  much 
harm  has  come  from  ignoring  it.  Frequently  it  is  of  extreme  importance. 
However,  it  is  important  to  the  cion  only  as  its  vigor  is  important  to  the 
cion  and  as  the  graft  union  is  satisfactory;  the  cion,  for  adjustment  to  one 
locality  or  purpose,  may  require  a  vigorous  stock;  for  adjustment  to 
another  locality  or  purpose  it  may  require  a  less  vigorous  stock  or  one 
that  thrives  in  a  soil  of  peculiar  character.  Adjustment  of  stock  to  cion, 
then,  should  be  made  with  these  factors  in  mind.  In  addition,  the  choice 
of  stock  should,  where  choice  is  possible,  be  made  with  soil,  pests  and 
cultural  practices  in  view;  conversely  these  should  be  considered  in  their 
relation  to  the  stock  as  well  as  to  the  top. 

INFLUENCE  OF  CION  ON  STOCK 

Instances  of  apparent  influence  of  cion  on  stock  are  more  striking  in 
plants  other  than  those  grown  for  their  fruit,  possibly  because  the 
interest  of  the  fruit  grower  is  centered  chiefly  in  the  cion  and  minor  influ- 
ences on  the  stock  are  less  likely  to  attract  attention.  Furthermore,  an 
influence  of  cion  on  stock  might  involve  a  reaction  on  the  cion  and  so 
be  attributed  to  the  effect  of  stock  on  cion.  However,  a  few  cases,  some 
undoubted  and  some  less  clearly  defined,  are  available  for  consideration. 

Just  as  among  the  influences  of  the  stock  on  the  cion,  the  effect  on 
vigor  and  form  of  the  cion  are  the  most  obvious,  possibly  because  most 


580  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

readily  observed,  so  among  the  effects  of  the  cion  on  the  stock  those  on 
vigor  and  form  of  the  stock  are  most  conspicuous. 

Size  and  Number  of  Roots. — Daniel/^  working  with  various  Cruciferse, 
found  that  in  some  cases  when  the  cion  belonged  to  a  species  of  greater 
height  than  that  of  the  stock  it  accelerated  the  growth  of  the  latter  and 
that,  when  conditions  were  reversed,  an  inhibiting  effect  was  exercised. 
Sahut^^^  stated :  "If  the  cion  belongs  to  a  more  vigorous  species  or  variety- 
it  stimulates  the  vigor  of  the  stock.  The  common  hawthorn,  grafted 
with  hawthorn  bearing  double  pink  flowers,  with  Sorbier  des  oiseleurs, 
Azerolier  d'ltalie  and  the  common  Rohinia  grafted  with  R.  decaisneana, 
develops  much  more  rapidly.  It  is  the  same  with  the  majority  of  Euro- 
pean vines  [grapes]  when  grafted  on  American  York  Madeira  or  Rupestris 
stocks  which  are  less  vigorous.  If  the  cion  is  less  vigorous  it  restrains 
the  vegetation  of  the  stock.  The  Dwarf  peach  of  Orleans,  grafted  on 
peach  or  almond,  and  Chinese  plums  on  Damascene  or  St.  Julien  [are 
examples].  It  is  the  same  with  the  majority  of  European  grapes  on 
Riparia  or  Jacquez." 

Instances  drawn  from  American  experience  are  not  lacking.  Swin- 
gle ^'*°  states:  "Although  the  Trifoliate  is  naturally  a  small  tree  and  of  slow 
growth,  when  used  as  a  stock  its  growth  is  so  stimulated  that  its  diameter 
always  continues  greater  than  that  of  the  scion.  .  .  .  This  form  of 
union  wherein  the  stock  slightly  outgrows  the  scion  has  been  noticed  also 
in  the  case  of  the  loquat  grafted  on  the  quince  growing  at  Eustis,  Fla. 
In  this  case,  also,  the  variety  so  grafted  began  to  bear  when  still  very 
young  and  has  borne  abundant  crops  since."  Bonns^"  confirms  the 
large  growth  of  the  trifoliate  stock,  even  while  it  is  exercising  a  dwarfing 
effect  on  the  lemon  tops  worked  on  it. 

Brown^^  states  that  the  Myrobalan  root  system  is  larger  than  usual 
if  it  is  worked  with  peach  tops. 

Bioletti  and  dal  Piaz^^  compare  Zinfandel  and  Tokay  grapes  growing 
on  Rupestris  St.  George  stocks.  Here  the  stocks  are  cuttings  and  there- 
fore even  more  comparable  than  most  seedling  stocks.  The  greater 
growth  of  the  Zinfandel  top  is  balanced  by  a  corresponding  development 
of  the  root  system. 

Whether  the  cause  be  incompatibility,  poor  graft  union  or  something 
else,  there  is  apparently  sufficient  evidence  to  warrant  the  statement 
that  in  some  cases  the  cion  does  influence  the  stock.  Since  pruning 
the  top  of  any  tree,  regardless  of  the  stock,  tends  to  reduce  the  root 
system  and  since  some  dwarf  trees  are  kept  so  only  by  heading  back, 
the  necessity  for  seeking  a  mysterious  influence  is  not  apparent.  A 
top  which  will  not  grow  vigorously  may  be  expected  to  act  on  the  stock 
as  would  a  heavy  pruning;  a  top  which  is  able  to  supply  the  roots  with 
abundant  food  may  be  expected  to  increase  their  growth.  Nevertheless, 
caution  should  be  exercised  against  ascribing  too  much  to  this  effect. 


THE  RECIPROCAL  INFLUENCES  OF  STOCK  AND  CION  581 

Some  grape  stocks  cannot  grow  fast  enough  to  supply  some  cions;  the 
sand  cherry  cannot  be  developed  by  a  vigorous  top  to  the  size  necessary 
for  the  successful  support  of  a  rapidly  growing  plum.  If  the  implied 
effect  of  stock  on  cion  be  admitted,  limitation  in  that  of  cion  on  stock  is 
obvious. 

Distribution  and  Character  of  Roots. — Possibly  because  the  root 
systems  of  nursery  plants  come  under  observation  much  more  than 
those  of  the  same  plants  once  they  are  set  in  orchard  or  vineyard,  there 
is  considerable  evidence  of  an  effect  of  cion  on  stock  in  young  fruit  plants. 
Nurserymen  frequently  identify  certain  pear  or  apple  trees  by  their 
root  systems,  though  all  are  on  seedling  stocks.  Hovey,'""  however, 
himself  a  nurseryman,  indicated  that  this  could  not  be  done  in  all  cases; 
some  strong  growing  varieties,  he  stated,  would  have  strong,  and  weak 
growers  such  as  Winter  Nelis  would  have  correspondingly  weak,  root 
systems.  It  is  stated  that  the  roots  of  trees  grafted  with  Siberian  Crab 
"  generally  run  down  more  than  those  of  other  trees. "  ^''*' 

Murneek^^^  states:  "Upright  growing  varieties  of  apples  of  the 
Russian  type,  for  instance,  will  form  a  correspondingly  deep  growing 
root  system  while  those  of  the  Winesap  type  will  be  flat  and  shallow. 
This  can  be  extended  even  to  particular  varieties.  The  Red  Astrachan, 
Oldenburg,  Fameuse,  for  example,  form  each  a  characteristic  root  system 
of  its  own.  In  this  connection,  Shaw  believes  'that  the  size  or  stoutness 
of  the  main  branches  is  positively  correlated  with  the  size  of  the  main 
roots  and  angle  of  the  branch  with  the  angle  of  the  main  roots  and  the 
axis  of  the  tree.  In  many  individual  cases  this  correlation  is  obscure, 
yet  careful  observations  with  large  numbers  of  trees  will  reveal  it.' " 
Bailey^  stated  that  Northern  Spy  and  Whitney  tops  make  the  roots 
of  the  stock  grow  deeper  than  usual. 

Waugh,!^^  discussing  plum  propagation,  reported:".  .  .  Stoddard 
tops  seem  to  give  some  of  the  curved  tap-root  character  of  the  Americanas 
to  all  the  stocks  on  which  they  grow.  .  .  .  One  interesting  point  was  in 
the  way  in  which  Stoddard  tops  induced  a  conspicuous  branching  of  the 
root  system  when  worked  on  peach.  With  other  varieties  the  peach 
gave  almost  always  a  clean,  unbranched  tap-root.  The  weak  growth 
of  Green  Gage  naturally  served  to  induce  only  a  weak  growth  in  most 
of  the  stocks  on  which  it  was  worked;  while  the  rampant  growth  of 
Chabot  had  exactly  the  opposite  effect.  The  strongly  branching  root 
systems  found  on  Chabot  trees  were  probably  due  in  part  to  the  energetic 
way  in  which  the  foliage  acted  during  the  growing  season.  Marianna 
stocks,  which  seemed  to  be  uncongenial  to  Milton,  giving  only  a  poor 
union,  made  very  little  growth  when  grafted  with  Milton  scions.  No 
other  case  was  observed  in  which  Milton  appeared  to  have  any  influence 
on  its  stock.  Newman  seemed  to  influence  all  stocks  in  the  way  of 
giving  off  more  secondary  roots.     Nearly  all  stocks  when  grafted  with 


582  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Newman  gave  a  strong,  vigorous  growth,  considerably  above  the  average, 
tending  at  the  same  time  to  produce  more  both  of  secondary  roots  and 
of  fibers."  In  the  following  year  he  reported:  "No  case  was  observed 
this  year  in  which  the  scion  showed  any  marked  effect  on  the  stock. "^^^ 

Baco^  cites  numerous  grape  stocks  in  which  the  roots  grow  more 
spreading  when  grafted  with  Baroque;  among  these  are:  Riparia 
Gloire,  Rupestris  du  Lot  and  Riparia  X  Rupestris  3306.  On  the  other 
hand,  Chasselas  X  Berlandieri  41  5  becomes  deeper  rooted  when  grafted 
with  the  same  cion  variety.  This  last  stock,  it  is  said,  succeeds  best  in 
warm,  dry  seasons  and  the  deeper  penetration  of  the  roots  is  held  to  be 
disadvantageous  in  many  locations  and  seasons. 

Longevity,  Growing  Season  and  Hardiness. — Some  rather  spectacu- 
lar instances  of  modification  in  growing  habits  of  stocks  are  reported. 

Linderauth^^  grafted  an  Abutilon  cion  on  the  roots  of  an  annual  plant,  Modiola 
caroliniana,  and  thereby  kept  the  combination  plant  alive  3  years  and  5  months. 
Althcea  narhonnensis  has  tops  which  die  to  the  ground  every  winter.  Grafted 
with  Abutilon  Thompsoni,  a  plant  of  Althcea  with  no  other  top  could  not  secure 
the  proper  materials  for  forming  winter  buds  and  died.  Another  specimen, 
similarly  grafted,  but  sending  out  a  sucker  from  the  root,  lived  and  kept  the 
cion  living  over  a  year.  DanieP'  obtained  similar  results  with  Solanum 
puhigerum  on  Giant  tobacco,  which  is  an  annual  in  Brittany. 

Sahut^^^  cites  numerous  instances  of  evergreen  cions,  as  Cratcegus  glabra 
and  Raphiolepis  on  the  common  quince,  etc.,  succeeding  on  deciduous  stocks. 
However,  these  cases  lose  some  of  their  significance  in  the  light  of  present  knowl- 
edge of  winter  processes  in  deciduous  plants.  The  same  writer  states  that  when 
the  late  opening  St.  Jean  walnut  is  grafted  on  the  common  walnut  the  stock  "is 
obliged  to  hold  back  a  month  or  more.  Deciduous  cherries,"  he  states,  "on 
the  Laurier-Amande  (evergreen)  make  the  stock  rest  almost  absolutely.  The 
varieties  of  grape  which  push  out  late,  Carignane,  for  example,  grafted  on  Riparia 
or  other  American  species  which  start  sensibly  earlier,  hold  the  stock  back.  The 
European  early  starting  grapes,  as  Aramon,  when  on  late  American  stocks,  as 
York  Madeira,  force  the  stock  to  earlier  growth." 

Perhaps  more  definite  information  may  be  secured  from  certain 
instances  where  the  cion  appears  to  have  an  effect  on  hardiness. 
Since  this  is  in  many  cases  a  matter  of  maturity  the  effects  recorded  may 
be  considered  equally  as  effects  on  maturity. 

Vard^'*^  in  an  extensive  survey  following  the  severe  winter  of  1890-1891  in 
France  found  that  rose  stocks  which  had  supported  cions  of  Tea  and  Bourbon 
roses  had  not  only  lost  their  cions  but  were  themselves  killed  back  to  the  ground. 
Unbudded  stocks  or  those  which  had  supported  hardy  varieties  suffered  Uttle. 

Following  the  cold  whiter  of  1913  in  Cahfornia  Webber  and  others  found  some 
apparent  cases  of  "a  definite  influence  of  the  tops  upon  the  stocks.  In  one  case," 
they  report,  "in  the  spring  of  1912  a  nursery  of  gour  seedlings  was  budded  to 
Eureka  lemons.     Many  of  these  buds  did  not  take,  so  that  during  the  freeze  of 


THE  RECIPROCAL  INFLUENCES  OF  STOCK  AND  CION  583 

January,  1913,  there  were  in  this  nursery,  at  the  same  elevation  and  under  the 
same  conditions,  yearling  lemon  tops  on  sour  stock  (buds  had  been  inserted 
several  inches  above  the  ground)  alongside  of  sour  seedlings.  While  a  shght 
injury  to  the  foliage  was  the  only  harm  experienced  by  the  latter,  the  lemon 
tops  were  killed,  and  the  frozen  wood  extended  3  to  4  inches  down  on  the  sour 
stock.  Similar  conditions  were  found  on  pomelo  stock  while  the  pomelo  seedlings 
were  scarcely  touched. "^^^ 

Other  Influences. — Sahut  states  that  quince  roots  topworked  to  pear 
are  more  particular  in  their  soil  requirements  than  those  not  worked  over; 
they  require  a  more  fertile  soil.  However,  as  he  indicates,  the  general 
rule  is  to  the  contrary;  otherwise  the  selection  of  lime  resistant,  drought 
resistant  and  moisture  resistant  stocks  would  be  to  no  point.  The  cion 
itself  does  not  render  the  stock  subject  to  phylloxera  or  immune  to 
woolly  aphis,  though  a  lack  of  congeniality  may  induce  weakness  and 
hence  a  lack  of  recuperative  power.  The  transmission  from  cion  to  stock 
of  variegation  has  been  discussed  previously;  it  cannot  be  regarded  as  an 
instance  of  true  influence  exerted  on  the  stock  by  the  cion. 

In  General. — Just  as  in  the  case  of  stock  on  cion,  in  considering  the 
influence  of  cion  on  stock  it  is  not  necessary,  so  far  as  fruit  plants  are 
concerned,  to  predicate  any  direct  effect  other  than  on  vigor.  Every 
other  influence  that  has  been  established  or  attributed  can  be  explained 
as  exercised  indirectly  through  vigor  and  can  be  placedoon  a  quantitative 
basis.  This  action  on  vigor  may  be  direct  when  the  two  parts  to  the 
graft  are  congenial  and  make  a  good  union,  or  it  may  be  indirect  when 
there  is  apparent  uncongeniality  and  the  union  is  poor.  Qualitative 
influences,  such  as  the  passage  of  alkaloids  across  the  graft,  or  the  barring 
of  inulin  by  the  graft,  are  not  necessary  to  explain  any  observed  phe- 
nomena resulting  from  grafting  in  fruit  plants. 


CHAPTER  XXXII 

THE  ROOT  SYSTEMS  OF  FRUIT   PLANTS 

The  choice  of  stocks  for  the  various  fruits,  where  any  considerable 
latitude  is  possible,  is  frequently  rather  complex.  First,  two  economic 
interests  are  concerned,  the  grower's  and  the  nurseryman's;  second, 
several  natural  factors,  the  congeniality  of  the  union  involved,  the 
relation  of  the  stock  to  the  soil,  to  the  climate  and  to  the  variety.  Rarely 
is  it  possible  to  secure  a  stock  that  meets  all  requirements  in  all  situations; 
the  result  is  generally  a  compromise. 

CONFLICTING  INTERESTS  OF  NURSERYMAN  AND  FRUIT  GROWER 

The  nursery  business,  like  most  businesses,  is  competitive.  The 
individual  nurseryman  is,  therefore,  sometimes  compelled  to  adopt 
certain  alternative  choices  which  may  not  be  to  the  best  interest  of  the 
grower  or,  ultimately,  of  the  nursery  business  itself.  The  responsibility 
for  this  situation  rests  not  with  the  nurseryman  alone,  for  as  long  as 
growers  will  buy  cheap  trees,  ignoring  their  real  value  for  the  conditions 
under  which  they  are  to  be  grown,  all  nurseries  are  more  or  less  forced 
to  offer  cheap  trees  and  often  find  difficulty  in  selling  better.  The 
nurseryman's  immediate  interest,  then,  rests  in  securing  stock  that 
is  cheap,  that  makes  a  good  union,  with  a  high  percentage  of  successful 
grafts,  and  that  makes  a  marketable  tree  quickly. 

The  plums,  with  the  multiplicity  of  species  cultivated  for  fruit  and  of 
species  available  for  stocks,  serve  as  an  excellent  illustration  of  con- 
flicting interests  and  factors.  Some  years  ago  it  became  evident  that  for 
successful  plum  culture  in  the  north  central  states  a  very  hardy  stock 
was  necessary.  The  Americana  stocks  met  the  growers'  requirements 
very  well  in  nearly  all  respects.  However,  seed  for  growing  the  stocks 
in  large  quantities  was  not  readily  available.  The  Marianna  stock, 
rooting  readily  from  cuttings  in  the  south,  was  much  cheaper.  Trees 
on  Marianna  roots  could  be  produced  at  little  expense  and  were  sold  at  a 
price  which  virtually  precluded  competition  from  the  better  suited,  but 
higher  priced,  trees  on  Americana  roots.  Want  of  discrimination  on  the 
part  of  buyers  of  nursery  stock  made  this  situation  possible.  Waugh 
furnishes  another  illustration.  The  St.  Julien  plum,  he  states,  is  the 
best  stock  for  Domestica  plums,  making  ''a  better,  stronger,  longer-lived 
tree  than  Myrobolan."  He  proceeds  to  quote  a  nurseryman's  letter, 
in  part,  as  follows:  "St.  Julien  stocks  are  much  preferred  by  the  orchard- 

584 


THE  ROOT  SYSTEMS  OF  FRUIT  PLANTS  585 

ists  in  this  locality,  because  trees  certainly  do  better  in  every  way  on  that 
stock.  They  sprout  less  from  the  root,  are  longer-lived,  and  generally 
more  vigorous  than  when  on  Myrobolan  stocks.  We  occasionally  plant 
some  St.  Julien  seedlings,  but  do  not  make  a  practice  of  it,  because 
in  the  first  place  St.  Julien  seedlings  cost  more  than  double  the  price  of 
Myrobolans,  and  they  are  not  as  thrifty  the  first  year  they  are  trans- 
planted. They  also  are  attacked  by  a  fungus  which  causes  them  to  lose 
their  leaves  early  in  the  summer,  thus  preventing  the  budding  of  the 
stocks  altogether,  or  a  partial  failure  in  the  buds  when  this  leaf  fungus  is 
not  corrected.  Of  course,  when  taken  in  time  we  can  in  a  large  measure 
prevent  this  falling  of  the  leaves  by  spraying  with  Bordeaux  mixture,  but 
taking  all  things  into  consideration,  it  is  quite  a  bit  more  expensive  to 
raise  plums  on  St.  Julien  stock,  and  we  find  that  we  cannot  get  any  more 
for  them  in  the  open  market,  so  that  we  have  become  discouraged  growing 
stocks  on  the  St.  Julien  root."  Hedrick  quotes  J.  W.  Kerr  of  Maryland 
to  the  effect  that  though  for  that  section  he  prefers  the  peach  as  a  stock 
for  the  Domestica  plums,  there  are  many  varieties  of  this  species  that 
will  not  form  a  good  union  with  the  peach  and  in  these  cases  he  is  forced 
to  use  Marianna  or  Myrobolan  stock. 

Growers  of  Vinifera  grapes  have  found  that  no  one  stock  is  suitable 
to  all  conditions.  Cuttings  of  a  given  species  may  not  root  freely  and 
it  is  eliminated  from  the  list  of  available  stocks,  no  matter  how  resistant 
it  may  be  to  phylloxera  or  how  desirable  in  other  respects.  Another 
species  or  variety  may  not  give  a  large  percentage  of  successes  in  bench 
grafting  and  the  establishment  of  a  vineyard  on  this  stock  becomes  a 
matter  of  more  labor  and  greater  expense. 

Dawson^^  gives  the  scarcity  of  seed  as  the  chief  reason  against  the 
employment  of  Pyrus  hetulafolia  which  he  states  would  be  a  very  satisfac- 
tory stock  for  pears  on  dry  soil. 

The  Mazzard  stock  for  cherries  is  preferred  by  growers  in  some  sec- 
tions, but  nurserymen  have  rather  forced  the  use  of  Mahaleb.  The 
Mazzard  has  several  features  which  make  it  rather  unsatisfactory  for  the 
nurseryman;  one  of  these  is  its  sensitiveness  to  weather  conditions  in 
the  nursery  row  so  that  though  buds  may  take  readily  one  season  the 
following  year  may  give  entirely  unsatisfactory  results,  or  the  budding 
season  may  close  abruptly  before  the  work  is  complete. ^^ 

Enough  evidence"  has  been  introduced  to  show  that  the  best  stock  for 
the  nurseryman,  under  existing  circumstances,  is  not  always  best  for  the 
grower.  The  responsibility,  however,  rests  with  the  grower.  When  he 
is  so  convinced  of  the  superiority  of  a  given  stock  that  he  is  willing  to  pay 
the  price  for  it,  the  nurseryman  will  produce  trees  on  that  stock.  Until 
the  grower  realizes  that  the  best  stock  in  the  orchard  may  not  be  the 
best  stock  in  the  nursery  or  vice  versa  the  nurseryman  can  do  only  as  he 
has  been  doing. 


586  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

ADAPTATION  OF  STOCKS  TO  PARTICULAR  CONDITIONS 

Further,  it  must  be  remembered  that  a  plant  that  is  valuable  to  the 
grower  in  one  location  may  prove  otherwise  in  another.  Climatic  condi- 
tions may  simplify  the  choice  for  a  certain  grower  by  eliminating  all 
but  the  most  hardy  stocks,  but  they  may  complicate  matters  for  the 
nurseryman  who  is  selling  to  a  wide  territory. 

Adaptation  to  Soil  Temperatures. — A  grower  ordering  stock  from  a 
nursery  in  a  milder  climate  should  consider  that  he  may  be  getting  trees 
with  stocks  not  adapted  to  his  conditions.  A  northern  grower,  for  exam- 
ple, securing  plum  trees  from  the  south,  would  do  well  to  make  sure  that 
they  are  not  on  peach  or  Marianna  roots,  though  some  of  the  leading 
nurseries  no  longer  use  these  stocks.  The  southern  grower  may  be  more 
interested  in  securing  a  stock  that  will  not  sucker  or  in  extreme  cases,  as 
cited  by  the  Howards,^"  he  may  even  require  a  stock  that  is  able  to  endure 
high  soil  temperature.  These  investigators  found  that  in  Baluchistan 
the  peach  and  plum  stocks  commonly  used  in  Great  Britian  would  not 
succeed,  but  by  using  stocks  which  they  considered  better  adapted  to  hot, 
dry  soils,  such  as  Marianna,  Myrobolan  and  Mahaleb,  they  secured  much 
better  results. 

Adaptation  to  Soil  Texture  and  Composition.^ — Prune  trees  in  the  Paci- 
fic northwest  have  been  planted  in  many  cases  without  much  regard  to  the 
stock  on  which  they  were  worked.  In  numerous  instances  prunes  with 
peach  roots  have  been  planted  in  rather  heavy,  poorly  drained  land  in 
which  the  planting  of  peach  trees  would  not  be  considered. 

French  horticulturists  had  not  solved  the  problem  presented  by  phyl- 
loxera when  they  had  isolated  certain  varieties  of  American  grapes  that 
were  resistant  to  this  pest,  that  lent  themselves  to  making  good  cuttings 
and  satisfactory  graft  unions  with  the  Vinifera  cions.  Many  of  the 
French  vineyard  soils  are  strongly  calcareous;  in  these  soils  only  compara- 
tively few  of  the  American  vines  flourish.  Hence,  ability  to  withstand 
calcareous  soils  must  be  considered  in  any  choice  of  stocks  for  rather  wide 
use  in  France.  When  California  vineyards  were  invaded  by  phylloxera 
the  stocks  tried  and  approved  in  France  were  naturally  given  early 
consideration.  However,  lime  tolerance  is  not  so  important  in  California 
since  comparatively  little  vineyard  soil  is  calcareous;  of  much  greater 
importance,  in  some  localities  in  this  state,  is  ability  to  withstand  di'ought, 
in  others  ability  to  flourish  in  soils  with  a  high  water  table  for  part  of  the 
year.  Rupestris  St.  George  (du  Lot),  because  of  its  deep  roots,  with- 
stands drought  better  but  suffers  severely  when  the  water  table  stands 
near  the  surface  for  long;  the  shallow  rooted  Riparia  Gloire  and  certain 
Berlandieri  hybrids  meet  requirements  here.  Most  Vinifera-American 
hybrids  adapt  themselves  to  these  conditions.  The  Muscadine  grapes 
also  are  adapted  to  moist  soils  and  hot  climates."^     In  California,  as  in 


THE  ROOT  SYSTEMS  OF  FRUIT  PLANTS  587 

France,  ignorance  of  local  conditions  and  of  the  stocks  suited  to  them  may 
indeed  lead  to  utter  failure. 

Other  plants  than  the  grape  prove  refractory  on  calcareous  soils  in 
France  and  in  many  cases  recourse  to  a  lime  resistant  stock  has  proved 
successful.  DentaP^  furnishes  an  instance  in  the  Australian  Acacia 
dealbata  which  grows  freely  in  calcareous  soils  on  A .  floribunda  though  on 
its  own  roots  it  will  not  grow  in  such  soils.  A  similar  expedient  is  neces- 
sary for  the  growth  of  certain  pines  in  these  soils.  Some  Australian  exper- 
ience seems  to  indicate  that  sour  orange  is  the  best  stock  for  orange  and 
lemon  in  sections  where  the  irrigation  water  is  likely  to  contain  alkali 
in  considerable  quantities. '^^  California  experience  indicates  that  lemon 
is  unusually  susceptible  to  alkali.^''  On  the  other  hand,  lemon  roots  are 
stated  to  be  the  best  foragers  in  poor  soils  in  this  section.  Primus  davi- 
diana  is  now  under  trial  in  Cahfornia  as  an  almond  stock;  the  particular 
quality  commending  it  is  its  ability  to  grow  in  more  alkaline  soils  than 
other  commonly  used  almond  stocks.^*-  Two  successive  plantings  of 
peaches  in  one  California  orchard  were  killed  by  alkali;  following  this 
peaches  on  Davidiana  roots  have  proved  successful  in  the  same  soil.^^' 
Cock^^  states  that  the  trifoliate  orange,  though  it  is  too  dwarfing  in  its 
effects  to  be  a  commercial  success,  may  be  used  to  advantage  in  very  wet 
soils.  In  the  Gulf  States  the  trifoliate  succeeds  in  rich,  moist  soils  and  is 
unsuited  to  light,  dry  soil.^^^  Pomelo  in  California  appears  to  suffer 
most  from  drought.-*^  Sahut^^'^  states  that  in  wet  soils  the  peach  and 
apricot  grow  better  on  plum  roots  than  on  their  own  or  on  almond  roots 
and  that  the  cherry  on  Mahaleb  grows  in  poor  soils  where  it  would  not 
grow  on  its  own  roots. 

The  degree  of  refinement  to  which  adaptation  of  stocks  can  be  carried  is  shown 
by  Bioletti's  tentative  recommendations  of  stocks  for  Vinifera  grapes  in  Cali- 
fornia :-^ 

"The  Rupestris  St.  George  has  given  its  best  results  in  the  hot,  dry  interior  on 
deep  soils.   .    .    . 

"For  a  great  majority  of  our  soils  and  varieties  the  two  Riparia  X  Rupestris 
hybrids  3306  and  3309  promise  to  be  superior  in  every  way  to  the  St.  George. 
The  former  for  the  moister  soils  and  the  latter  for  the  drier.   .    .    . 

"For  the  wettest  locations  in  which  vines  are  planted — in  places  where  the 
water  stands  for  many  weeks  during  the  winter,  or  where  the  bottom  water  rises 
too  near  the  surface  during  the  summer— the  most  promising  stock  is  Solonis  X 
Riparia  1616. 

"For  moist,  rich,  deep,  well-drained  soils,  especially  in  the  coast  counties  and 
on  northerly  slopes,  the  St.  George  is  utterly  unsuited.  The  crops  on  this  stock, 
in  such  locations,  are  apt  to  be  small,  and  the  sugar  content  of  the  grapes  defec- 
tive. In  these  locations  the  Riparia  Gloire  is  much  to  be  preferred,  and  will 
undoubtedly  give  larger  crops  of  better  ripened  grapes. 

"None  of  the  above  stocks  give  good  results,  as  a  rule,  in  very  compact  soils. 


588  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

For  such  soils  the  most  promising  varieties  are  106^  in  the  drier  and  Aramon  X 
Rupestris  No.  1  or  202^  in  the  wetter  locations.  In  dry,  shallow  soils  420A 
and  157^^  give  promise  of  being  excellent  stocks." 

Some  stocks  show  such  cathohcity  in  taste  that  it  is  safe  to  grow  trees 
on  them  for  planting  in  all  locations  that  are  at  all  suited.  The  Cah- 
fornia  black  walnut,  for  example,  adapts  itself  to  so  many  soils  that  it  is 
almost  universally  used  in  California  as  stock  for  the  English  (or  Persian) 
walnut,  though  its  resistance  to  root  rot  {Armillaria  mellea)  is  also  an 
important  factor. 

Sorauer^^*  quotes  Lieb  to  the  effect  that  Pyrus  mains  prunifolia 
major  and  P.  m.  baccata  cerasiformis  have  been  found  valuable  as  stocks 
for  apple  in  very  exposed  or  dry  positions. 

Immunity  or  Resistance  to  Soil  Parasites. — Adaptation  to  soil  must 
be  paralleled  at  times  by  adjustment  to  diseases.  The  Damson  plum 
seems  rather  resistant  to  crown  gall  and  in  special  cases  might  be  given 
preference  for  this  reason.  Shaw  has  found  that  cion-rooted  apple  trees 
show  crown  gall  in  different  forms  according  to  variety.  "Thus,"  he 
states,  "the  Jewett  apple  shows  usually  if  not  always  the  hard  form  of  the 
gall,  the  Red  Astrachan  the  simple  form  of  the  hairy  root  and  the  Olden- 
burg the  woolly  knot  form  with  many  soft  fleshy  root  growths.  Other 
varieties  show  the  brown  root  form  and  still  others  often  the  aerial 
form.    .    .    . 

"Some  varieties  on  their  own  roots  seem  to  be  largely  if  not  entirely 
immune  to  this  disease.  If  this  proves  to  be  really  the  case,  here  may  lie 
the  solution  of  the  problem  of  the  prevention  of  crown  gall.  .  .  .  Prob- 
ably the  economic  advantage  would  warrant  the  extra  effort  necessary  to 
propagate  such  trees,  only  under  conditions  where  the  crown  gall  was 
especially  troublesome. 

"There  are  other  root  diseases  which  are  injurious,  especially  through 
the  southern  part  of  the  apple  belt,  that  might  possibly  be  avoided  in  a 
similar  fashion." '^^ 

The  pear  affords  an  interesting  example.  The  so-called  Japanese 
pear  (Pyrus  serotina)  is  more  resistant  to  blight  than  the  French  stock,  but 
seems  rather  susceptible  to  mushroom  root  rot  and  is  sensitive  to  soil 
moisture.  Choice  between  the  two  may  at  times  involve  nice  discrimi- 
nation. In  some  soils  the  lemon  suffers  from  root  rot  to  such  an  extent 
that  other  stocks  are  substituted.  In  Florida  the  sweet  orange  roots 
formerly  used  as  stocks  were  so  badly  attacked  by  root  rot  that  this 
stock  has  been  superseded.  Similar  susceptibility  is  found  in  California. 
In  regions  subject  to  pear  blight  the  displacement  of  French  seedling 
pear  stock  by  other  stocks,  such  as  Pyrus  serotina,  P.  ussuriensis  and 
P.  calleryana,  that  are  resistant  or  immune  can  be  forecasted,  except  as 
other  troubles  may  develop. 


THE  ROOT  SYSTEMS  OF  FRUIT  PLANTS  589 

PROPAGATION  BY  CUTTINGS 

Under  this  head  are  considered  the  various  forms  of  cuttings,  layers, 
stools  and  the  like  which  depend  on  the  formation  of  roots  from  the  wood 
of  the  variety  to  he  cultivated,  without  the  intervention  of  grafting  or  bud- 
ing.  All  plants  thus  propagated  are  on  their  own  roots.  The  list  of  fruit 
plants  so  propagated  commonly,  includes  the  fig,  olive,  grape,  currant, 
gooseberry,  mulberry,  filbert  and  pomegranate  from  hardwood  cuttings; 
the  various  dwarfing  apple  stocks  and  quince  from  mound  layers  or  stools; 
the  strawberry  by  rooted  "runners;"  the  black  raspberry,  loganberry  and 
dewberry  by  rooted  tips  of  canes,  the  red  raspberry  and  blackberry  by 
suckers;  the  cranberry  and  blueberry  by  hard  or  soft  wood  cuttings  or 
by  "tubering"  or  "stumping"  as  the  case  may  be.  If  pomological 
literature  be  searched  at  all  carefully  there  appear  some  rather  sur- 
prising additions  to  the  list  of  plants  that  can  be  propagated  by  cuttings, 
particularly  by  hardwood  cuttings,  including  frequently  the  citrus  fruits, 
plums,  pears  and  apples. 

"Some  of  the  plums  grow  well  from  cuttings.  This  is  especially  true  of 
Marianna,  and  millions  of  Marianna  cuttings  are  made  every  year  in  this  coun- 
try, mostly  for  stocks.  .  .  .  The  St.  Julien  plum  grows  fairly  well  from  cut- 
tings, and  nearly  all  the  Myrobolan  varieties  may  be  propagated  this  way.  Some 
of  the  Japanese  varieties,  especially  Satsuma,  have  been  grown  from  cuttings 
in  the  southern  states.  Practically,  however,  propagation  by  cuttings  is  con- 
fined to  the  Marianna.  "^^"^ 

That  the  apple  may  be  propagated  by  cuttings  is  indicated  by  quota- 
tions from  Knight,  though  possibly  he  is  describing  what  is  now  known  to 
be  a  rather  common  pathological  condition  in  the  apple. 

"There  are  several  varieties  of  apple  tree,  the  trunks  and  branches  of  which 
are  almost  covered  with  rough  excrescences,  formed  by  congeries  of  points  which 
would  have  become  roots  under  favorable  circumstances;  and  such  varieties  are 
always  very  readily  propagated  by  cuttings."*^  The  Paradise  and  Doucin 
stocks  root  more  or  less  readily  from  cuttings. 

Darwin^^  cites  Tennent  as  saying,  "in  the  Botanic  Gardens  of  Ceylon  the 
apple  tree  sends  out  numerous  underground  runners  which  continually  rise  into 
small  stems,  and  form  a  growth  around  the  parent  tree." 

Ribston  Pippin  is  said  in  England  to  grow  readily  from   cuttings. 

Again  quoting  Knight:  "Peach  and  Nectarine  trees,  particularly 
of  those  varieties  which  have  been  recently  obtained  from  seed,  may  be 
propagated  readily  by  layers,  either  of  the  summer  or  older  wood;  and 
even  from  cuttings,  without  artificial  heat;  for  such  strike  root  freely. "^^ 

Advantages  and  Disadvantages. — Propagation  by  cuttings  may  or 
may  not  be  advantageous;  there  is  nothing  in  the  process  itself  that  makes 
it  one  or  the  other.  When  it  is  readily  accomplished  it  is  obviously  the 
cheapest  process,  but  the  plant  may  do  better  on  some  other  roots  than  its 


590  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

own.  The  lemon,  for  example,  is  reported  in  Australia'*"  as  inferior  on 
its  own  roots,  being  more  susceptible  to  unfavorable  soil  moisture  con- 
ditions. The  Vinifera  grapes  root  readily  from  cuttings  but  the  roots  so 
formed  are  subject  to  phylloxera  infestation;  recourse  is  therefore  made  to 
grafting  these  grapes  on  resistant  stocks  which  in  turn  are  grown  from 
cuttings.  The  Oldenburg  apple  on  its  own  roots  appears  decidedly 
inferior, ^^•^  though  Mcintosh  and  Stayman  make  notably  fine  growth  on 
their  own  roots.  Sometimes  when  it  would  be  desirable  to  have  trees  on 
their  roots  their  failure  to  root  readily  from  cuttings  makes  the  process  im- 
practicable. Many  of  the  apples  and  plums  that  are  extremely  resistant 
to  cold  winter  weather  form,  if  set  deeply,  roots  from  the  cion  that  are 
much  hardier  than  those  of  the  stocks  commonly  supplied.  A  method  of 
ready  propagation  by  cuttings  in  such  cases  would  be  of  great  advantage. 
To  meet  this  difficulty  special  methods  have  been  devised;  these  are  dis- 
cussed presently.  To  take  advantage  of  the  relative  immunity  of  North- 
ern Spy  roots  to  the  woolly  aphis,  Australian  growers  take  considerable 
pains  to  develop  these  roots,  either  by  layering,  stooling  or  grafting  with  a 
"starter,"  and  upon  the  Spy  stock  work  the  variety  they  wish  to  grow. 
In  some  cases,  then,  fruit  plants  which  grow  readily  from  cuttings  are 
grafted  on  other  stocks  at  greater  expense;  in  other  cases,  plants  which  do 
not  form  their  own  roots  readily  are  induced  to  do  so,  though  such  plants 
are  more  expensive. 

Objection  is  sometimes  made  to  plants  propagated  by  cuttings  as 
compared  with  those  developed  on  seedlings,  because  of  certain  supposed 
shortcomings.  They  are  occasionally  said  to  be  shallow  rooted ;  Hatton,^° 
however,  states,  regarding  dwarf  apple  stocks:  "We  have  found  it  just 
as  possible  to  raise  stocks  of  deep  anchorage  by  layers  and  other  vegeta- 
tive methods  as  it  is  easy  to  find  shallow-rooted  ones  in  any  collection  of 
free  stocks  raised  from  pips."  This  supposed  shallowness  of  the  root 
system  was  turned  to  account  by  the  early  Spanish  settlers  of  Louisiana, 
who  propagated  the  peach  by  layering  to  suit  it  to  alluvial  lands  where  the 
water  table  is  high.^^^  Cock,^**  writing  on  citrus  fruits  in  Victoria,  states 
that  layers  and  cuttings  are  always  weak  and  more  liable  to  disease  than 
seedlings.  Macdonald,^"^  also  in  Victoria,  writing  of  the  olive,  states: 
"It  is  possible  that,  in  poor  soils  or  trying  situations,  the  seedling  may  be 
the  more  thrifty  and  long-lived  tree,  but  experience  in  this  country  has  not 
gone  to  prove  that  this  is  the  case.  Many  of  the  oldest  trees  in  Australia 
were  raised  from  truncheons  and  are  still  doing  well.  However,  their  age 
is  comparative  youth  in  the  life  of  the  olive  tree,  and  perhaps  it  is  as  well 
to  accept  the  opinion  of  continental  writers  on  the  greater  longevity  of 
seedling  trees  until  there  is  greater  evidence  at  hand  to  the  contrary." 

In  New  South  Wales  seedling  plums  are  considered  to  make  better 
root  systems  than  cuttings.^  Grapes,  gooseberries  and  currants  have 
passed    through    many    generations    of    cuttings,    without    perceptible 


THE  ROOT  SYSTEMS  OF  FRUIT  PLANTS  591 

diminution  in  vigor.  The  process,  therefore,  apparently  is  not  per  se 
devitalizing.  It  has,  moreover,  certain  marked  advantages,  one  of 
which  is  uniformity  of  the  roots. 

This  uniformity  in  the  roots  frequently  is  of  considerable  importance. 
The  constant  tendency  to  variation  in  seedlings  is  not  confined  to  quality, 
color  and  size  of  the  fruit  but  extends  to  every  character  of  the  plant. 
They  may  vary  in  vigor  of  growth  as  much  as  in  the  color  of  the  fruit; 
the  (juality  of  fruit  varies  no  more  than  the  stature;  the  depth  of  rooting, 
resistance  to  cold,  to  drought,  to  moisture,  to  alkali,  all  are  variable 
characteristics.  Hatton^''  states:  "Free  stock  is  a  comprehensive  term, 
meaning  no  more  than  seedlings  which  include  dwarf  stocks  both  fibrous 
and  stump-rooted,  as  well  as  vigorous  ones  resulting  from  a  well-balanced 
root  system."  The  seedling  root,  then,  is  in  a  measure  an  unknown 
quantity.  The  tree  planted  in  the  orchard  is  standardized  above  ground, 
uncertain  below  ground.  The  stock  for  any  individual  tree  may  be  more 
vigorous  or  more  hardy  or  more  resistant  than  the  average;  it  is  just  as 
likely  to  be  less  so.  In  France  the  prospective  grape  grower  whose  soil  is 
strong  in  lime  knows  that  certain  stocks  do  not  thrive  on  those  soils ;  he  is 
able  to  pick  a  lime-enduring  stock,  for  grape  root  stocks  have  been  stand- 
ardized through  growth  from  cuttings.  If,  however,  he  has  a  rocky, 
thin  soil  in  a  hot,  dry  exposure,  he  can  select  another  stock,  known  to  be 
the  best  for  such  locations.  Were  he  to  rely  on  seedlings  he  would  be 
indulging  in  a  lottery  whose  results  could  be  told  only  after  a  year  or  more. 
To  replace  those  which  failed  he  would  use  more  unknown  quantities. 

Grapes  in  Particular. — Varietal  differences  in  the  character  of  root 
systems  produced  from  cuttings  are  recognized  in  grapes.  Bioletti  and 
dal  Piaz"  explain  the  susceptibility  of  Riparia  and  the  immunity  of 
Rupestris  stocks  to  drought  by  the  shallow  roots  of  the  former  and 
the  deeply  penetrating  roots  of  the  latter.  In  poorly  drained  soils  and 
in  soils  with  the  water  table  high  for  any  length  of  time,  these  same 
peculiarities  tend  to  reverse  the  order  of  suitability.  Hedrick  sug- 
gests that  the  small  amount  of  winter  killing  of  grapes  on  Rupestris 
St.  George  stock  as  compared  with  that  on  other  stocks  in  an  experimental 
vineyard  in  New  York  may  have  been  due  to  its  deep  rooting  habit.''* 
The  advantage  of  having  stocks  of  known  performance  is  obvious. 

Apples  and  Pears  in  Particular. — Fortunately  apple  and  pear  stocks 
are  fairly  adaptable.  They  seem  so,  certainly— perhaps  because  there 
is  no  standard  with  which  to  compare  them.  However,  every  careful 
grower  recognizes  that  some  of  his  trees  consistently  bear  more  or  less 
than  others.  This  raggedness  may  be  attributed  to  minor  variations 
in  soil  and  doubtless  correctly  so  in  many  cases;  it  is  sometimes  attributed 
to  bud  variation,  though  the  work  of  Crandall^^  and  of  Gardner*^^  suggests 
the  doubtful  importance  of  this  source  of  variation.  The  unevenness 
in  a  seedling  orchard  strongly  suggests  that  were  the  tops  all  removed 


592  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

and  grafts  of  one  variety  inserted  on  the  roots  the  resulting  trees  would 
show  considerable  differences  in  vigor  and  productiveness.  Mention 
is  made  elsewhere  of  results  in  Missouri  showing  considerable  variation 
in  seedling  apples. 

Hatton'"'  states,  in  the  course  of  a  comparison  of  Paradise,  free  and  crab 
stocks:  "We  are  faced,  then,  with  two  converging  series  quite  arbitrarily  divided, 
the  one  ranging  from  dwarfness  to  vigour  and  the  other  from  vigour  to  dwarf- 
ness;  the  only  real  distinction  being  that  the  Paradise  series  has  been  raised 
vegetatively,  and  any  particular  meml^er  of  the  series  can  be  reproduced  by  that 
method  again  and  again,  whilst  the  free  series  has  been  raised  from  seed,  and  as 
long  as  this  method  is  employed  infinite  variety  and  inequahty  will  continue, 
except  in  rare  cases. 

"It  is  often  argued  that  'true  crabs'  are  less  variable  than  'ordinary  free 
stocks'  but  I  cannot  learn  what  the  trade  distinction  stands  for.  If  free  stocks 
are  the  chance  children  of  cider  fruits,  crabs  (commercial  not  botanical)  are  the 
chance  progeny  of  wildings;  but  every  district  has  many,  many  so-called  crabs 
varying  in  vigour  and  character.  I  have  seen  them  strong  and  clean;  dwarfing 
and  root  knotted,  whilst  the  types  of  fruit  are  various.  I  do  not  pretend  to 
assert  that  free  stocks  from  particular  sources  may  not  be  more  even  than  from 
other  sources.  That  simply  depends  on  the  chance  crosses,  on  the  varieties 
mixed  or  cross  pollinated,  which  in  some  cases  may  be  more  advantageous  than 
in  others;  but  I  do  say  that  stocks  raised  from  pips  will  always  be  variable,  and 
therefore  incompletelj^  satisfactory,  except  for  the  purpose  of  raising  new  types 
of  stock  for  subsequent  vegetative  propagation,  if  we  find  degeneration  or  im- 
perfection in  the  existing  types." 

Examination  of  an  orchard,  injured  here  and  there  by  root  killing, 
forces  belief  in  the  variation  shown  by  the  seedling  roots  and  an  apprecia- 
tion of  the  desirability  of  a  stock  that  is  uniformly  hardy.  If  a  vigorous, 
hardy,  resistant  stock  could  be  isolated  and  propagated,  much  of  the 
unevenness  in  yield  and  uncertainty  in  hardiness  would  be  eliminated. 

Furthermore,  the  importance  to  the  experimenter  of  having  each  tree 
on  its  own  roots  should  be  emphasized.  The  lack  of  uniformity  in 
yields  of  trees  in  the  same  plot  in  fertilizer,  cultural  or  pruning  experi- 
ments has  done  much  to  invalidate  results  and  more  definite  conclusions 
might  well  be  expected  if  the  root  systems  as  well  as  the  tops  of  the  trees 
were  identical. 

Vegetative  propagation  of  apple  stocks  seems  not  only  of  probable 
value  but  worthy  of  study  as  a  real  possibility.  Hatton^*^  in  a  paper 
of  great  importance  reports  that  in  the  investigations  of  Paradise  apple 
stock  at  East  Mailing  one  type  was  isolated  which  is  free  growing,  not 
in  the  least  dwarfing  in  its  effects;  this  stock  is  propagated  readily  by 
vegetative  methods.  Further  study  of  this  type  and  search  for  others 
like  it  seem  of  great  importance.  The  great  amount  of  variation  found 
by  Hatton  gives  promise  of  isolating  stocks  which  will  show  particular 


THE  ROOT  SYSTEMS  OF  FRUIT  PLANTS  593 

adaptabilities  to  different  conditions  in  a  manner  comparable  to  those 
now  catalogued  for  grapes  and  of  making  possible  much  finer  fitting 
of  trees  to  environment. 

Propagating  Apples  and  Pears  by  Layerage  and  Hardwood  Cuttings. — 
Investigation  of  propagation  of  apples  and  pears  by  hardwood  cuttings 
seems  of  possible  value  as  well.  These  cuttings  root  readily  in  the 
tropics  and  in  some  of  the  southern  states,  such  as  Florida,  Mississippi 
and  Texas,  and  could  perhaps  be  rooted  elsewhere  if  proper  soil  tempera- 
tures were  provided.  Kieffer  and  LeConte  among  pears  and  Northern 
Spy  among  apples  seem  to  root  especially  well,  though  this  ability 
is  possessed  by  other  varieties.  Similar  cases  have  been  reported  in 
England. 

Warcollier  in  France  is  reported  to  have  had  mediocre  results  with 
cuttings  of  30  to  50  centimeters  of  the  previous  season,  well  ripened; 
success  was  possible  only  with  soft  wooded  varieties.  Others  in  France 
reported  very  satisfactory  results  using  branches  of  3  or  4  years'  growth, 
with  side  growths  removed,  plunged  into  the  soil  to  a  depth  of  10  to  25 
centimeters.  Varieties  of  moderate  or  feeble  vigor,  particularly  one 
known  as  "Petit  doux, "  gave  the  best  results. "■* 

The  propagation  of  the  Northern  Spy  stocks  used  for  all  apples  in  Victoria 
is  chiefly  from  layers  and  stools.  The  parent  Spy  stocks  are  planted  2  feet  apart 
in  rows  4  or  5  feet  distant  in  June  (autumn  in  Australia).  The  processes  followed 
are  described  by  Cole:*°  "In  August  cut  back  to  within  an  inch  of  the  ground 
level,  so  as  to  get  a  supply  of  buds  to  or  below  the  soil  to  push  out.  The 
following  August  cut  back  to  two  buds  any  weak  or  light  growth,  pegging  down 
the  stronger  parallel  with  the  row  or  other  planted  stocks.  The  buds  upon  the 
pegged-down  growths,  being  now  brought  into  a  vertical  position,  will  send  up  a 
sufficient  supply  of  shoots  for  working  upon  sound  lines.  About  November, 
mould  them  up  lightly  by  removing  some  of  the  higher  soil  from  the  middle  of 
the  rows.  During  the  following  winter  remove  soil  about  the  layers  and  cut 
away  any  light  shoots  that  may  have  rooted  hardening  back  others  close  to 
the  main  layer. 

"The  propagator  should  not  be  too  eager  in  removing  rooted  shoots  from  the 
main  laj^ers  until  after  the  fourth  season,  but  will  be  repaid  by  cutting  hard  back, 
forming  good,  well-rooted  crowns  for  future  use.  From  now  out  the  operator 
mil  require  to  use  his  own  judgment  regarding  the  growths  he  cuts  hard  back  and 
those  he  leaves  for  pegging  down  after  removing  any  that  may  be  rooted.  In 
the  winter  mould  up  after  cutting  away  any  rooted  stocks  and  the  pegging  down 
is  finished,  and  again  in  November  or  December.  Deep  or  over  moulding  should 
be  avoided. 

"  Stooling. — This  method  is  somewhat  similar  to  that  of  layering,  but  instead 
of  pegging  down  the  unrooted  shoots  they  are  cut  hard  back  each  year,  so  as  to 
encourage  as  many  as  possible  to  show  out.  The  second  season  from  planting, 
and  after  the  shoots  have  been  cut  back  to  within  an  inch  or  so  of  the  stool,  mould 
lightly,  and  again  in  November  or  December.     If  the  shoots  do  not  root,  this 


594  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

moulding  will  cause  them  to  become  bleached  close  to  the  crown  of  the  stool. 
Upon  being  hardened  back,  shoots  that  give  the  best  results  will  be  formed. 
When  removing  rooted  shoots  in  the  winter,  leave  any  that  are  very  small  for 
the  following  year;  also  any  that  are  weak  and  spindly.   .    .    . 

"The  cooler  and  moister  districts  are  the  best  adapted  for  the  raising  of  Spy 
stocks  by  these  two  methods  (layering  and  stooling),  as  the  rooting  of  the  shoots 
is  controlled  by  even  moisture  during  late  summer  and  early  autumn.  From 
healthy,  old,  and  well  estabhshed  stools,  and  those  putting  up  medium  and  not 
over-strong  shoots,  the  best  results  are  obtained.  The  writer  advises  that  layer- 
ing and  stooling  should  be  worked  conjointly." 

The  use  of  Northern  Spy  stock  is  mentioned  by  Wickson^^^  in  CaUfornia. 
Paul  C.  Stark,  however,  states  that  Northern  Spy  has  not  proved  satisfactory 
in  the  central  states,  as  a  stock,  forming  knots  on  the  roots  and  rooting  with 
some  difficulty. 

In  the  northern  central  states  where  seedling  roots  have  proved 
tender  in  the  colder  winters  recourse  has  long  been  made  to  an  indirect 
method  of  securing  trees  on  their  own  roots.  Long  cions  are  wliip  grafted 
on  small  pieces  of  seedling  roots  and  planted  deep.  Roots  are  formed 
more  or  less  freely  from  the  underground  portion  of  the  cion;  since  the 
varieties  grown  are  necessarily  hardy  the  roots  seem  to  share  in  this 
hardiness  and  have  proved  actually  hardier  than  the  average  seedling 
roots.  In  a  short  time  these  cion  roots  generally  outgrow  the  seedling 
starter  which  becomes  much  reduced  in  proportion  and  plays  an  insig- 
nificant part  in  the  mature  tree. 

Varietal  Differe7ices  and  Contributing  Factors. — Varieties  differ  in  the 
readiness  with  which  they  emit  roots  in  this  way.  Shaw^^"  found  that 
some  varieties  root  readily,  others  only  in  very  niggardly  fashion; 
Baldwin,  for  example,  showing  32  per  cent.,  Ben  Davis  51,  Sweet  Bough 
98,  Delicious  22,  Mcintosh  74,  Jonathan  11,  Grimes  41,  Gravenstein  55, 
Northern  Spy  58,  Oldenburg  25,  Tolman  3,  Winesap  34,  Wolf  River  71, 
Yellow  Bellflower  3,  Yellow  Transparent  26.  He  found  also  that  the 
same  variety  performs  differently  from  year  to  year,  possibly  from 
internal  conditions,  possibly  from  external.  Stark  reports  that  Delicious 
forms  cion  roots  very  readily  and  the  roots  are  aphis  resistant.  Moore^^^ 
reports  on  similar  work  in  Wisconsin.  Of  the  varieties  tested  Livland 
Raspberry,  Hyslop,  McMahon,  Pewaukee  and  Transcendent  showed  cion 
roots  on  50  per  cent,  of  the  trees  studied,  in  the  third  year.  Cion  roots 
are  formed  more  readily  in  moist  soil  and,  because  of  this,  Moore  con- 
cludes that  grafts  planted  deep  form  roots  more  readily.  Table  8, 
reproduced  from  Moore's  report,  shows  the  difference  in  cion  root  forma- 
tion in  moist  and  in  dry  soil. 

Recent  investigations  in  Iowa  show  that  the  formation  of  cion  roots 
is  much  accelerated  by  winding  the  point  of  grafting  tightly  with  a 
copper  wire.^^ 


THE  ROOT  SYSTEMS  OF  FRUIT  PLANTS 


595 


Table  8. — Cion    Roots   Produced   in  Apple  under  Different  Soil  Moisture 
Conditions     (After  Moore^^^) 


Trees  observed 

Cion-rooted 

Strong  cion-rooted 

Variety 

Moist 

Dry 

Moist, 
per  cent. 

Dry, 
per  cent. 

Moist, 
per  cent. 

Dry, 
per  cent. 

Peerless 

Northwestern 

Mcintosh 

Hyslop 

McMahon 

263 

142 

94 

40 

31 

311 

328 
110 
98 
103 

42.6 

63.4 

56.4 

100.0 

87.1 

31.4 
24.1 
29.1 
50.0 
32.0 

6.1 

18.3 

21.3 

100.0 

58.0 

5.8 

2.7 

1.8 

23.5 

10.7 

Maynard^"^  mentions  the  use  of  short  pieces  of  apple  roots  as  nurse 
grafts  for  refractory  quince  cuttings.  "The  apple  root,"  he  states, 
"supplies  moisture  and  a  little  food  material  until  roots  are  formed  on 
the  cion,  when  it  fnils  to  grow  more,  and  we  have  the  quince  on  its  own 
root." 

Another  method  of  propagating  trees  on  their  own  roots  is  the  plant- 
ing of  own  rooted  trees  secured  as  just  described  and  taking  cuttings 
from  the  roots  they  form.  This  depends  on  the  formation  of  adven- 
titious buds  on  the  roots  which  some  species  and  some  varieties  accom- 
plish readily  while  others  apparently  do  not. 

Finally  should  be  mentioned  propagation  of  fruit  trees,  especially 
some  of  the  plums  and  some  varieties  of  apple,  from  sprouts  arising  on 
the  roots.  This  method  is  perhaps  more  common  in  some  sections  of 
Europe  than  in  the  United  States,  partly  because  the  varieties  grown  lend 
themselves  to  this  treatment  and  partly  because  of  the  very  positive,  if 
somewhat  exaggerated,  prejudice  in  the  United  States  against  root 
stocks  which  sprout  freely. 


SOURCES  OF  NURSERY  STOCK 

With  certain  reservations  it  may  be  said  that  the  proximity  of  the 
source  of  nursery  stock  is  unimportant.  If  the  stock  is  healthy,  well 
developed  and  well  matured,  it  will  grow.  Some  of  the  ornamentals, 
grown  from  seed,  tend  to  mature  earlier  if  from  northern  seed  than  if  from 
southern  and  there  may  be  temporarily  a  somewhat  readier  response  to 
climatic  changes  in  vegetatively  propagated  plants  from  one  section  than 
from  another  but,  if  there  is,  it  quickly  disappears  and  there  is  little  or  no 
evidence  that  it  is  of  any  practical  importance. 

It  should,  however,  be  reaUzed  that  different  stocks  are  used  in  grow- 
ing certain  fruits  by  nurseries  in  different  parts  of  the  country  and  that 
this  may  be  of  extreme  importance.     The  northern  plum  grower,  for 


596  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

example,  is  more  likely  to  get  hardy  plum  roots  from  a  nursery  near  home 
than  he  is  from  a  nursery  whose  chief  clientage  is  in  a  section  with  milder 
winters. 

For  fall  planting,  northern  growers  will  be  more  likely  to  get  well 
ripened  trees  from  northern  sources  where  the  trees  naturally  mature 
earlier.  That  this  may  assume  importance  is  shown  in  the  section  on 
Temperature  Relations. 

Withal  the  mere  mailing  of  an  order  to  a  local  nursery  is  not  always  a 
guarantee  that  the  stock  sent  to  fill  the  order  is  of  local  origin.  Many 
nurseries  buy  much  of  their  stock  from  distant  points.  However,  if  the 
stock  is  good  and,  in  cases  where  a  difference  in  roots  is  important,  if  the 
roots  are  of  the  right  kind,  the  grower  need  not  concern  himself  greatly 
about  its  origin. 

GRADES  OF  NURSERY  STOCK 

Fruit  trees  are  offered  for  sale  by  nurseries  in  several  grades,  which 
are  based  on  size  as  measured  by  either  height  or  diameter  or  both.  Since 
the  largest  trees  cost  the  most,  the  question  whether  there  is  any  ultimate 
advantage  in  them  is  of  practical  importance. 

The  very  fact  of  the  grading  shows  the  difference  between  individuals. 
If  this  is  a  temporary  matter,  due  to  better  immediate  environment  of 
one  tree  in  the  nursery  row  there  will  be  no  final  difference  in  the  growth 
and  performance  of  these  trees.  If,  however,  the  variation  be  an  expres- 
sion of  inherent  differences,  the  planting  of  lower  grade  stock  may  have 
serious  consequences. 

It  is  shown  elsewhere  in  this  section  that  bud  mutations  in  the  decidu- 
ous fruits  are  uncommon;  hence,  uniformity  in  the  tops  may  be  presumed. 
If  there  be  a  fundamental  difference  between  the  large  tree  and  the  small 
tree  in  the  nursery  the  cause  must  lie  in  the  stock.  Most  of  the  stocks 
used  are  seedlings  and  therefore  more  variable  than  the  vegetatively 
propagated  stocks,  some  kinds  more  than  others.  Some  of  this  variation 
is  undoubtedly  temporary,  but  there  are  good  reasons  for  thinking  some 
of  it  is  more  deeply  seated. 

Webber^^i  reports  investigations  with  citrus  fruits  that  bring  out  these 
inherent  differences  in  seedling  stocks  very  strikingly. 

He  summarizes  his  investigations  in  part  as  follows: 

"Nursery  trees  even  when  grown  from  selected  buds  taken  from  selected 
trees  differ  greatly  in  size  when  they  reach  transplanting  age.  Commonly  the 
large  trees  are  sold  first  and  the  small  trees  later  when  they  reach  the  required 
size. 

"Large,  medium  and  small  nursery  trees  of  Washington  navel  and  Valencia 
oranges  and  Marsh  grapefruit  grown  in  comparative  tests  show  that  after  2H 
years  in  the  orchard  the  large  trees  remain  large,  the  intermediate  trees  remain 


THE  ROOT  SYSTEMS  OF  FRUIT  PLANTS  597 

intermediate  and  the  small  remain  small.  The  evidence  indicates  that  this 
condition  is  inherent  in  the  trees  and  that  in  planting  orchards  only  the  large 
nursery  trees  should  be  used. 

"An  examination  of  sweet  and  sour  orange  seedling  stock,  such  as  is  used  for 
budding,  showed  the  presence  of  many  widely  different  types.  Some  of  these 
types  were  propagated  and  the  trees  at  the  end  of  the  4H  years  still  show  the  same 
marked  difference.  Some  are  fully  five  times  as  large  as  others.  Yet  all  such 
types  are  used  as  stocks. 

"Budding  on  seedhng  stocks  of  different  types  and  unknown  character  of 
growth  is  believed  to  be  largely  responsible  for  the  different  sizes  of  budded 
trees  developed  in  the  nurseVy  and  also  for  many  of  the  irregularities  in  size  and 
fruitfulness  of  orchard  trees." 

These  differences  probably  hold  for  the  apple.  A  seedling  apple 
orchard  seven  years  planted,  at  the  Missouri  Station,  contains  trees  rang- 
ing in  circumference  from  one  inch  to  sixteen.  It  is  not  likely  that  if 
these  seedling  roots  had  been  topworked  to  the  same  variety  they  would 
all  have  made  equally  good  trees.  From  all  appearances,  they  have 
maintained  or  increased — but  not  changed — their  relative  differences 
in  size;  the  trees  that  are  largest  have  made  good  growth  each  year, 
while  those  that  are  now  inferior  appear  to  have  been  inferior  continuously. 

It  should,  however,  be  recalled  that  there  are  cases  of  a  delayed  effect 
in  dwarfing.  Plums  worked  on  sand  cherry  frequently  make  vigorous 
growth  in  the  first  year,  greater  in  fact  than  on  other  stocks  which  ulti- 
matel}^  grow  the  larger  trees. 

Gravenstein,  on  the  Paradise  apple  in  Germany  is  said  to  grow  very 
vigorously  at  first,  but  to  grow  very  little  after  bearing."^  Chester 
Pearmain  and  other  varieties  behave  similarly.  ^^  Like  effects  have  been 
recorded  with  Castanea  vulgaris  grafted  on  Quercus  sessiliflora  in  an  attempt 
to  grow  chestnut  in  soils  strong  in  lime;  growth  was  very  vigorous  the 
first  year,  but  few  grafts  lived  till  the  third  year.  Even  shorter  was  the 
success  of  Vinifera  grapes  on  Cissus  orientalis  Lamarck. ^-^  Hatton'"' 
may  be  quoted  on  this  point:  "It  is  often  denied  that  this  inequality  in 
the  stocks  shows  itself  in  the  worked  trees.  Although  it  is  true  that  a 
strong-growing  variety,  such  as  Bramley's  Seedling,  may  largely  obliterate 
this  inequality  in  the  maiden,  differences  again  become  apparent  in  the 
second  and  third  years."  To  this  extent,  then,  the  grower  buying  2-year 
old  graded  stocks  of  some  trees  may  perhaps  be  a  little  surer  of  having 
runts  weeded  out.  At  present,  however,  the  extent  to  which  this  delayed 
effect  is  operative  in  common  fruits  cannot  be  stated. 

Briefly,  in  buying  nursery  stock,  the  grower  who  gets  trees  of  good 
size  for  their  age,  other  things  equal,  is  more  nearly  sure  of  getting  trees 
that  will  do  well  in  his  orchard.  Buying  the  smaller  grades  he  is  buying 
uncertain  plants.  They  may  be  stunted  only  and  may  ultimately 
make  good  trees.     They  may,  however,  be  composed  of  runts  which  are 


598  FUNDAMENTAL."^  OF  FRUIT  PRODUCTION 

inherently  incapable  of  being  anything  else.  In  practice  the  inferior 
grades  probably  contain  some  stunted  and  some  "runt "  trees.  The  only 
sure  way  of  differentiating  between  them  is  the  test  of  time  which  is 
likely  to  prove  more  costly  to  the  grower  than  the  difference  in  price. 
The  inferior  grades,  therefore,  should  be  regarded  with  suspicion. 

On  the  other  hand,  the  extremely  large  tree  is  open  to  objections,  seri- 
ous in  some  cases.  If  the  tree  is  large  only  because  it  is  older,  only  be- 
cause it  has — as  often  happens — stood  in  the  nursery  an  extra  year  or  two, 
it  carries  no  guarantee  of  inherent  good  growth;  on  the  contrary,  the 
presumption  is  against  it.     It  may  be  only  an  elder  runt. 

Gardeners  know  well  that  the  smaller  the  plant  the  less  disturbance 
it  suffers  in  transplanting  and  the  more  readily  it  reestablishes  itself.  A 
large  proportion  of  the  root  system  of  the  larger  trees  is  cut  off  in 
digging.  Data  gathered  in  California  show  that  the  largest  trees  made 
the  smallest  percentage  diameter  increase  during  the  first  year  in  the 
orchard,  indicating  a  slowness  in  adjusting  themselves  to  the  new  loca- 
tion." Furthermore,  trees  of  unduly  large  size,  produced  sometimes  by 
over  irrigation  or  heavy  fertilization,  are  more  liable  to  winter  injury  when 
planted  in  the  autumn. 

Other  objections  to  the  larger  trees  are  voiced  by  Hendrickson  :^^ 
"Branches  are  often  produced  the  first  year  in  the  nursery  row.  If 
these  branches  could  be  utilized  they  would  be  a  distinct  advantage  but 
they  are  often  broken  or  injured  in  the  process  of  packing  and  must  be 
cut  off  when  the  tree  is  planted.  In  other  cases  the  branching  does  not 
begin  near  the  bottom  of  the  tree  or  the  bottom  branches  have  been 
shaded  out,  and  hence  it  is  difficult  to  secure  a  low-headed  tree  by  using 
the  branches  produced  in  the  nursery.  Furthermore,  the  buds  on  the 
lower  portion  are  far  apart  and  the  tree  has  a  tendency  to  grow  from  the 
top  buds.    .    .    . 

"The  small  1-year  old  tree  as  a  rule,  depending  on  the  kind,  produces 
few  or  no  side  branches.  Consequently  the  buds,  instead  of  growing  into 
branches  in  the  nursery,  remain  dormant  until  the  following  year.  They 
are  also  less  liable  to  injury  in  packing.  Consequently  the  small  tree 
within  a  few  weeks  after  the  beginning  of  the  growing  season  is  covered 
from  top  to  bottom  with  leaves  and  small  branches.  The  growth  is 
generally  more  evenly  distributed  among  the  several  growing  points, 
than  in  the  case  of  the  overgrown  tree." 

Withal,  "large"  and  "small"  sizes,  or  even  grades  based  on  definite 
measurements,  are  relative  only.  Different  nursery  fields,  or  the  same 
fields  in  different  years,  produce  trees  varying  considerably  in  size. 
Varieties  differ  more  or  less  in  their  characteristic  growths.  Conse- 
quentl}''  even  among  trees  of  the  same  age  any  grading  must  be  on  a  rela- 
tive basis;  a  certain  caliper  measurement  may  denote  small  trees  in  one 
case  and  medium  sized  trees  in  another. 


THE  ROOT  SYSTEMS  OF  FRUIT  PLANTS  599 

Definite,  though  not  invariable,  objections  have  been  shown  to  both 
extreme  grades  in  nursery  stock,  on  the  one  hand  practical  and  on  the 
other  hand  primarily  theoretical  but  none  the  less  real.  The  logical 
consequence  is  the  approval  of  the  medium  grades.  Experience  usually 
justifies  this  course. 

Selection  of  Seedling  Stocks. — For  good  or  evil,  seedling  stocks  will 
continue  in  use,  for  some  fruits,  indefinitely.  It  is  likely,  however,  that 
at  no  distant  time  the  sources  of  seedling  stock  will  receive  closer  scrutiny 
than  has  been  given.  Indeed  a  rough  selection  has  been  exercised  for 
many  years  in  some  cases.  The  so-called  Vermont  crab  stock  for  apples, 
in  reality  grown  from  cider  mill  pomace  and  tracing  ultimately  in  many 
cases  to  seedling  apples,  sometimes  has  been  preferred  to  crab  stock. 
Feral  peach  stock  from  Tennessee  has  been  used  to  a  considerable  extent. 

Gradually,  however,  imported  French  seedlings  have  been  used 
increasingly  for  apple  stocks,  because  they  were  cheaper  than  native 
grown  stock.  With  the  rise  of  canneries,  peach  stones  and  cherry  pits 
have  been  available  at  little  cost  to  growers  of  nursery  stocks  and  have 
been  widely  used. 

The  variation  in  seedlings  has  been  mentioned.  It  is  probable, 
however,  that  investigation  will  show  certain  varieties  to  produce 
larger  proportions  of  good  seedlings  than  others.  Commercial  varieties 
of  fruit  are  not  grown  for  the  value  of  the  seedling  stocks  they  produce. 
Doubtless  some  of  them  will  prove  of  value  for  this  purpose;  others  will 
not. 

Roeding'25  g^yg;  "For  several  j^ears  I  have  been  carrying  on  experiments 
with  different  varieties  [of  peaches]  todetermine  their  value  from  a  standpoint 
of  growth  and  general  freedom  from  crown  gall,  and  taking  it  all  in  all,  the  Salway 
comes  first,  and  the  trees  produced  from  Lovell  and  Muir  seed  next.  Within  the 
last  few  years  I  have  been  carrying  on  experiments  with  Tennessee  natural 
pits  and  am  already  convinced  of  their  value  as  to  the  vigor  of  growth.  If  the 
root  system  is  found  to  be  healthy  and  of  a  fibrous  character,  this  stock  will  be 
given  the  preference." 

Apple  seedlings  from  different  parentage  will  probably,  in  some  cases, 
show  differences  worthy  of  consideration.  Data  from  an  orchard  of 
seedhngs  of  known  parentage  at  the  Missouri  Experiment  Station" 
show  a  marked  tendency  to  inferior  growth  in  all  seedlings  of  Ralls 
(Geniton)  parentage.  Careful  study  doubtless  would  show  certain 
varieties  to  be  admirable  parents  for  nursery  stock,  while  others  would 
turn  out  to  be  parents  of  an  unduly  large  number  of  runts,  sources  of  loss 
both  to  nurseryman  and  to  grower. 

The  desirability  of  care  in  the  selection  of  the  source  of  seedling  stocks 
has  received  attention  in  Europe. 


600  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Duplessix,^^  writing  on  apple  growing  in  Brittany,  states:  "The  choice  of 
apple  trees  furnishing  seeds  for  sowing  is  very  important,  for  the  tree  coming 
from  the  seed  will  generally  have  the  principal  characters  of  that  tree  which 
supphed  the  seed.  But  there  are  numerous  varieties  whose  wood  has  a  slow, 
twisting  growth,  without  vigor,  and  these  varieties  are  not  suitable  for  generating 
good  stocks,  which  ought  to  be  straight  and  of  a  vigorous  and  rapid  growth. 
Other  varieties,  as  most  of  the  Reinettes  and  Calvilles,  are  very  subject  to  canker; 

"  It  is  necessary  then  to  extract  the  seeds  from  fruits  from  trees  whose  wood  is 
healthy  and  of  a  very  vigorous  growth.  Right  here  is  a  difficulty  for  cultivators, 
for  the  wood  varieties  generally  used  by  nurserymen,  such  as  the  Frequin  de 
Chartres,  Noire  de  Vitry,  Genereuse  de  Vitry,  Maman  Lily,  yield  few  fruits  or 
fruits  of  second  quality  and,  for  this  reason,  are  almost  unknown  in  our  orchards." 

The  same  writer  carries  the  matter  of  selection  still  further  and 
advocates  growing  stock  from  seed  of  trees  corresponding  in  season  of 
growth  inception  with  those  whose  grafts  they  are  destined  to  bear. 

Grafted  or  Budded  Trees. — Certain  fruits  such  as  cherries  and  peaches 
are  propagated  customarily  by  budding  and  no  question  is  raised  as  to  the 
value  of  trees  produced  in  this  manner.  Some  others,  as  the  apple,  are 
readily  propagated  either  by  budding  or  by  grafting  and  the  question  of 
preference  between  trees  grown  by  these  methods  has  been  raised  fre- 
quently. There  may  be  a  difference  in  the  adaptability  to  a  given  locality 
of  budded  or  grafted  trees,  but  it  rests  on  a  basis  other  than  that  usually 
discussed. 

Much  of  the  alleged  superiority  of  budded  trees  rests  on  the  use  of  a 
whole  root  in  budding  while  in  bench  grafting  one  root  may  be  cut  to 
serve  three  or  four  cions.  It  is  argued  that  this  Cutting  down  of  the  root 
system  produces  a  tree  that  is  permanently  inferior  to  the  budded  tree. 
Budding  frequently  produces  a  larger  tree  in  a  given  time  in  the  nursery 
than  grafting,  but  there  is  no  positive  evidence  of  any  permanent  differ- 
ence in  trees  raised  by  the  two  methods  and  there  is  much  negative  evi- 
dence that  points  to  the  absence  of  any  difference  due  to  the  process  used 
per  se  or  the  amount  of  root  used  per  se. 

The  real  difference  between  budded  trees  and  grafted  trees  has  been 
appreciated  only  in  certain  sections  where  the  difference  was  brought 
out  occasionally  by  the  death  of  one  class  and  the  survival  of  the  other. 
Trees  grafted  with  long  cions  and  short  pieces  of  root  and  set  deep  in  the 
nursery  tend  to  throw  out  roots  from  the  cion,  while  the  seedling  root 
becomes  unimportant  or  dies,  as  explained  elsewhere.  Experience  has 
indicated  that  cion  roots  arising  from  wood  of  varieties  that  are  hardy  are 
themselves  more  uniformly  hardy  than  the  roots  on  which  they  are 
grafted.  Such  trees  are  therefore  better  adapted  to  localities  where  root 
killing  is  likely.  It  is  regrettable  that  in  recent  years  so  many  budded 
trees  have  been  set  in  northern  fruit  growing  sections  where  root  grafted 
cion  rooted  trees  provide  an  insurance  well  worth  consideration. 


THE  ROOT  SYSTEMS  OF  FRUIT  PLANTS  601 

Cion  rooted  trees  may  prove  superior  in  other  localities  because 
of  their  persistence  or  spread  or  depth  or  other  qualities.  If  experience 
with  grapes  is  a  valid  analogy,  considerable  difference  between  varieties 
is  these  qualities  would  appear  upon  investigation,  some  cion  roots 
proving  superior  and  other  inferior.  In  the  one  case,  then,  root  grafted 
trees  would  be  superior,  in  the  other,  budded  trees,  since  the  seedling 
roots  would  average  better  than  the  cion  roots.  In  sections  with  cold 
winters,  particularly  sections  with  scanty  snowfall,  root  grafted  trees 
should  be  used. 

Double  Worked  Trees. — There  are  several  possible  reasons  for  double 
working:  (1)  a  lack  of  congeniality  between  stock  and  cion,  (2)  need  of  a 
trunk  and  scaffold  limbs  that  are  mechanically  stronger,  (3)  the  top  may 
be  subject  to  disease  or  winter  injury  that  is  more  or  less  characteristic 
of  the  trunk. 

Certain  varieties  of  the  pear  unite  poorly  with  quince  stock  though 
they  unite  well  with  pear.  Therefore,  on  the  quince  is  worked  a  variety 
that  does  unite  well  and  into  this  as  a  stock  is  budded  the  desired  variety. 
Beurre  Hardy  is  used  by  many  nurserymen  as  the  linking  variety. 
Bailey^  recommends  Angouleme  for  the  same  purpose;  Rivers, ^^i  jj^ 
England,  found  a  number  of  varieties  useful,  including  Beurr^  d'Amanlis. 
Clairgeau  and  Seckel  are  among  the  varieties  said  to  thrive  better  when 
double  worked.  In  California  double  working  is  favored  for  Bartlett 
on  quince  roots. ^^^ 

Burbidge^^  mentions  another  combination  in  double  working:  "In  soils 
which  do  not  suit  the  Quince,  but  in  which  the  Pear  luxuriates,  this  order  may 
often  be  reversed  by  using  some  good-constituted  Pear  as  the  root  stock  on  which 
to  graft  the  Quince,  which  again  in  its  turn  is  worked  the  following  year  with 
the  kind  of  Pear  desired  to  form  a  fruiting  specimen."  He  also  quotes  Parkin- 
son (1629)  for  another  interesting  example:  "Speaking  of  the  red  Nectarine, 
then  the  rarest  and  dearest  of  all  fruit  trees,  he  remarks:  'The  other  two  sorts 
of  red  Nectarines  must  not  be  immediately  grafted  on  the  Plum  stock,  but  upon 
a  branch  of  an  Apricock  that  hath  been  formerly  grafted  on  a  Plum  stock.'  " 

The  apricot  as  described  by  Baltet^-  is  adjusted  to  dry  sites  along 
the  Mediterranean  by  almond  roots.  Since  the  grafts  do  not  take  well 
in  direct  contact,  double  working  is  invoked,  using  a  vigorous  peach  as 
the  connecting  link.  The  same  author  states  that  the  Damask  plum  is 
sometimes  used  in  France  as  intermediary  between  the  peach  top  and 
Myrobolan  roots.  ^^ 

Certain  varieties  of  apples  are  notoriously  subject  to  collar  rot. 
To  escape  this  difficulty  they  may  be  worked  on  another  variety  that 
is  noted  for  its  resistance.  Grimes  double  worked  on  Delicious  in  the 
nursery  is  now  available.  Delicious  is  said  to  induce  \igorous  growth, 
transforming  Bechtel  Crab,  for  example,  into  a  much  more  satisfactory 


602  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

tree  than  the  ordinary  seedhng  stocks  develop.  It  is  probable  that  more 
of  this  kind  of  double  working  will  be  employed  in  the  future. 

Blight  resistant  kinds  of  pear  are  coming  into  use  as  stock  on 
which  the  more  susceptible  but  better  flavored  pears  are  worked.  The 
"Japanese"  pear  has  been  used  for  this  purpose,  with  results  varying 
because  several  species  have  been  imported  under  this  name.  Some 
are  comparatively  tender,  others  are  uninjured  by  a  temperature  of 
-40°F.  or  even  lower;  some  are  comparatively  susceptible  to  blight,  others 
practically  immune.  Among  the  more  promising  of  these  stocks  are  Pyrus 
ussuriensis,  P.  ovoidea  and  P.  calleryana.^^'^  The  first  of  these  is  extremely 
hardy;  the  last  is  comparatively  hardy  and  is  able  to  thrive  in  very  wet 
soils.  There  is  no  doubt  that  working  of  dessert  varieties  in  limbs  of  these 
trees  will  greatly  decrease  the  labor  and  cost  of  fighting  pear  blight. 

Top  working  to  insure  hardiness  in  the  trunk  is  discussed  elsewhere. 
It  may  be  mentioned  here,  however,  that  the  use  of  Rome  Beauty  trunks 
for  Gravenstein,  the  leading  apple  variety  in  the  Sebastopol  apple  section 
of  California,  has  prevented  the  "sour-sap,"  which  has  been  exceedingly 
troublesome  there. ^''^ 

An  interesting  possibility  in  the  future  of  fruit  growing  in  America 
is  top  working  for  the  development  of  a  .better  framework.  Increasing 
competition  will  ultimately  tend  toward  the  use  of  fruit  of  high  quality. 
Heretofore,  varieties  with  good  quality  in  fruit  but  weak  growing  habits 
have  been  discarded;  enhanced  appreciation  of  quality  is  likely  to  force 
the  fruit  grower  to  use  such  varieties  whether  he  likes  the  tree  or  not. 
With  weak  growing  varieties  he  will  likely  resort  to  top  working  on  frames 
formed  by  more  sturdy  varieties.  For  this  reason  it  is  interesting  to 
note  that  in  growing  certain  choice  dessert  varieties  many  European  grow- 
ers have  followed  this  practice  for  a  long  time.  Certain  plums,  as  Petit 
Mirabelle,  which  are  weak  growers,  are  worked  into  a  sturdy  interme- 
diary such  as  Quetsche,  Reine  Claude  de  Bavay,  St.  Catherine,  Krasensky 
or  Andre  Leroy.^^  In  Algeria  the  Japanese  plums  grow  better  when 
top  worked  into  peach  limbs.  The  same  process  is  followed  with  several 
pears.  Growers  of  choice  apples  appear  to  resort  to  similar  devices  for 
Baltet  lists  numerous  varieties  as  suitable  intermediaries  and  states  that 
nurserymen  grow  certain  varieties  especially  for  this  purpose. 

According  to  Lindemuth  double  worked  apple  trees  have  been  in 
great  favor  in  Holland.  A  variety  called  "Sweet  Pippin"  is  grafted 
into  seedhng  stocks  close  to  the  ground  and  on  this  intermediary  the 
fruiting  variety  is  worked  at  the  height  of  the  head.  The  sole  reason 
for  this  preference,  it  is  said,  is  the  thick  trunk  formed  by  the  Sweet 
Pippin,  obviating  the  necessity  of  supporting  the  young  tree  during 
its  first  few  years  by  a  stake.  Since  apple  trees  in  northern  Europe 
are  grown  commonly  with  much  higher  heads  than  in  the  United  States 
this  precise  quality  would  be  more  important  there. 


THE  ROOT  SYSTEMS  OF  FRUIT  PLANTS  603 

Maynard^"^  rccommonds  working  Bosc,  a  notoriously  poor  growing 
pear,  into  tops  of  strong  growing  varieties  such  as  Ansault,  Clapp  or 
Flemish  Beauty.  In  sections  particularly  subject  to  pear  blight,  how- 
ever, these  particular  frame  stocks  would  not  be  advisable.  Maynard 
stated  in  1909  that  Kieffer  had  been  recommended  for  this  purpose  but 
had  "not  been  successfully  tried  in  the  eastern  states." 

It  should  be  recorded,  perhaps,  that  double  working  was  advocated 
many  years  ago,  for  increasing  the  quantity  and  quality  of  fruit.  Graft- 
ing in  itself  was  supposed  to  have  this  effect  and  it  was  thought  as  voiced 
by  Noisette,  i''2  i\^^i  ^}^g  more  the  operation  was  repated  the  greater 
would  be  the  improvement.  In  more  recent  times,  however,  the  tendency 
has  been  to  use  double  working  for  more  specific  purposes,  or  not  at  all. 
Here  again,  as  in  so  many  cases,  distinction  must  be  made  between  the 
effects  of  the  process  itself  and  the  effects  of  the  material  used  in  the 
process. 

PEDIGREED  TREES 

Observation  commonly  shows  much  individual  variation  between 
the  trees  in  an  orchard  that  has  been  planted  and  tended  with  the  purpose 
of  providing  conditions  as  uniform  as  possible.  Furthermore,  these 
differences  extend  to  practically  every  feature  of  the  tree  growth  and 
they  are  often  extreme.  Naturally  this  has  suggested  the  possibility 
of  perpetuating  by  vegetative  propagation  the  favorable  variations. 
There  has  been  much  discussion  on  this  question  and  on  the  value  of 
the  so-called  "  pedigreed  "  trees  that  are  grown  from  cions  cut  from  indivi- 
duals of  unusual  excellence.  In  many  cases  very  little  actual  evidence 
has  been  available  and  opinions  have  been  based  on  an  assumed  analogy 
between  a  vegetatively  propagated  tree  and  a  sexually  reproduced  animal 
or  on  theoretical  considerations. 

Some  Results  with  Citrus  Fruits. — Shamel  and  some  of  his  associates 
have  clearly  demonstrated  that  in  a  number  of  the  varieties  of  citrus 
fruits  there  is  a  large  amount  of  bud  variation  that  is  of  real  significance. 
A  number  of  intra-variety  strains  have  been  isolated,  propagated  and 
have  "bred  true,"  if  such  an  expression  can  be  used  for  the  vegetative 
propagation  employed  in  the  citrus  fruits. 

The  following  quotations  from  the  reports  of  Shamel  and  his  associates  will 
make  clear  the  results  of  their  investigation:  "Thirteen  important  strains  [of 
Washington  Navel  orange]  have  been  found  in  the  investigational  performance 
record  plots. "^^^ 

"Twelve  important  strains  of  the  Valencia  variety  have  been  found  and 
described :"^^^  "The  lowest  percentage  of  off  type  tree,  i.e.  marked  variations 
from  the  best  or  Washington  strain,  found  in  commercial  orchards  have  been 
about  10  per  cent.,  and  the  highest  about  75  per  cent.,  of  the  total  number  of 


604  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

trees  in  the  orchard. "^^^  "Tree-census  observations  in  Navel  orange  orchards 
in  California  show  a  general  average  of  about  25  per  cent,  of  trees  of  diverse 
strains,  most  of  which  are  inferior  to  the  Washington  as  regards  both  the  amount 
and  the  commercial  quahty  of  the  fruit." 

"Occasional  limbs  have  been  found  in  such  trees  [Washington  strain]  pro- 
ducing typical  Golden  Nugget  fruits  consistently  from  year  to  year  during  the 
entire  period  of  observation.  .  .  .  The  variation  in  the  amount  of  annual 
crops  produced  by  a  given  series  of  individual  Washington  Navel  orange  trees 
is  relatively  uniform  throughout  the  series  each  year.  That  is,  the  highest 
producing  trees  in  any  one  year  are  in  general  the  highest  producing  ones  each 
year,  and  the  lowest  ones  remain  at  the  bottom  of  the  list  continually.  Indi- 
vidual trees  are  relatively  very  stable  over  a  series  of  years  in  the  character  and 
the  amount  of  their  production.  .  .  .  Suckers,  or  unusually  vigorous  non- 
bearing  branches  have  been  used  almost  universally  for  this  purpose.  This 
practice  has  led  to  the  propagation  of  a  continually  increasing  proportion  of 
trees  of  those  strains  producing  the  largest  amount  of  sucker  growth.  Inasmuch 
as  such  trees  are  usually  light  bearers  and  produce  inferior  fruits  this  practice 
has  been  unfortunate  and  is  the  direct  cause  of  the  presence  of  the  large  propor- 
tion of  unproductive  trees  found  in  many  orchards.  Fruit  bearing  bud  wood  has 
been  selected  from  limb  variations  occurring  in  trees  of  the  Washington  or  other 
strains  and  in  several  hundred  cases  where  the  growth  from  these  buds  has 
fruited  every  selection  has  come  true."^^^ 

With  such  fruits  pedigreed  is  to  be  preferred  to  common  stock  for  it 
represents  definite  types  of  strains  that  run  true,  when  there  is  consider- 
able uncertainty  as  to  what  to  expect  from  the  general  run  of  unselected 
stock.  Perhaps  "pedigreed"  is  an  unfortunate  term  to  apply  to  such 
selected  stock;  it  is  rather  "improved"    stock. 

Some  Results  with  Apples. — Hedrick^^  represents  fairly  well  one  school 
of  opinion  when  he  says,  concerning  "pedigreed"  apples: 

"At  the  very  outset  it  must  be  pointed  out  that  the  seeming  analogy  between 
plants  propagated  from  buds  and  cions  and  those  grown  from  seeds  has  given  a 
false  simplicity  to  the  fact  and  has  led  many  astray.  Analogy  is  the  most 
treacherous  kind  of  reasoning.  We  have  here  a  case  in  which  the  similarity  of 
properties  is  suggested  but  the  two  things  are  wholly  different  upon  close  analysis. 
In  the  case  of  seeds  there  is  a  combination  of  definite  characters,  in  the  offspring 
from  two  parents.  Since  the  combinations  of  characters  handed  down  from 
parents  to  children  are  never  the  same,  individual  seedhngs  from  the  same 
two  plants  may  vary  greatly.  On  the  other  hand,  a  graft  is  literally  a  '  chip  of  the 
old  block'  and  while  plants  grown  from  buds  may  vary  because  of  environment 
they  do  not  often  vary  through  heredity.  .  .  The  Geneva  Station  has  an 
experiment  which  gives  precise  evidences  upon  this  question  of  pedigreed  stock. 
Sixteen  years  ago  a  fertilizer  experiment  was  started  with  60  Rome  trees  propa- 
gated from  buds  taken  from  one  branch  of  a  Rome  tree.  Quite  as  much  varia- 
tion can  be  found  in  these  trees  from  selected  buds  as  could  be  found  in  an  orchard 
of  Romes  propagated  indiscriminately  and  growing  under  similar  condition. 
Data  showing  the  variations  in  diameter  of  tree  and  in  productiveness   .    .    . 


THE  ROOT  SYSTEMS  OF  FRUIT  PLANTS 


605 


will  go  far  to  convince  anyone  that  uniformity  of  behavior  as  regards  vigor  and 
productiveness  of  tree  and  size  and  color  of  fruit  cannot  be  perpetuated." 

In  1895  the  Missouri  Station  propagated  from  the  highest  and  from  the 
lowest  yielding  trees  in  an  orchard  of  over  200  Ben  Davis  then  in  full 
bearing.  The  resulting  trees  were  planted  alternately  in  orchard  rows 
and  individual  yield  records  were  kept  from  1912  to  1918  inclusive.  These 
are  summarized  in  Table  9,  which  shows  no  difference  in  favor  of  trees 
propagated  from  the  best  tree.  Though  there  was  a  difference  in  size  and 
•finish  of  the  fruit  in  the  original  trees  there  was  none  in  the  fruit  borne  by 
their  offspring.  Investigations  in  Vermont,  reported  by  Cummings,^^ 
show  no  consistent  superiority  in  cions  from  superior  trees  of  several 
varieties  of  apple. 

Table  9. — Avekage  Yields  of  Apple  Trees  Propagated  from   High-yielding 

AND  from  Low-yielding  Parents 

(After  Gardner^^) 


From  "good"  parent 

From  "poor"  parent 

(bushels) 

(bushels) 

1912 

6.1 

5.4 

1913 

7.0 

11.3 

1914 

10  2 

6.3 

1915 

7.1 

10.3 

1916 

4.7 

8.1 

1917 

11.4 

6.6 

1918 

4.2 

11.8 

Averaiie 

7,2  . 

8.5 

The  statement  has  often  been  made  that  cion  wood  taken  from 
certain  parts  of  the  tree  gives  rise  to  trees  that  are  better  than  those  pro- 
pagated from  less  carefully  selected  wood.  CrandalP^  has  given  this 
matter  thorough  investigation  in  the  apple  and  reports  the  following 
conclusions: 

"Summarized  data  giving  comparisons  between  trees  propagated  from  large 
buds  and  those  propagated  from  small  buds,  together  with  the  aggregate  of 
impressions  derived  from  careful  inspections  of  trees  of  all  groups,  admit  but  one 
conclusion,  namely,  that  there  are  no  differences,  for  purposes  of  propagation, 
between  buds  of  large  size  and  those  of  small  size. 

"Growth  curves  of  trees  propagated  from  buds  of  different  situations  on  the 
trees  so  closely  approximate  as  to  leave  no  basis  for  assuming  that  it  makes 
any  difference  from  what  situation  on  the  tree  the  buds  are  taken. 

"All  buds  from  healthy  shoots  are  of  equal  value  for  purposes  of  propagation, 
at  least  so  far  as  growth  of  tree  is  concerned. 


606  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

"Fluctuations  in  growth  of  individuals  within  particular  groups  are  decided, 
often  extreme.  In  general,  differences  become  less  with  increase  in  age,  provided 
the  trees  remain  healthy. 

"There  is  no  tangible  basis  upon  which  to  establish  the  assumption  that 
robust  scions  are  superior  to  scions  of  small  diameter  for  purposes  of  pro- 
pagation." 

These  conclusions  apparently  differ  from  those  of  Shamel,  Scott  and 
Pomeroy  working  with  citrus  fruits.  However,  it  should  be  noted  that 
sucker  growth  was  found  in  great  abundance  only  in  citrus  trees  that  were 
"off  type"  individuals  and  it  was  to  trees  from  such  parentage  that  these 
workers  particularly  referred.  In  other  words  it  was  only  because  excess- 
ive sucker  growth  was  correlated  with  a  certain  type  of  degeneration  that 
propagation  from  wood  of  that  kind  yielded  unsatisfactory  results  in 
practice.  The  evidence  seems  to  warrant  the  conclusion  that  normal 
buds,  whether  borne  on  slow  or  rapid  growing  shoots  or  on  suckers,  are 
satisfactory  for  propagation,  provided  they  are  healthy  and  do  not  come 
from  limbs  that  are  bud  mutations.  Furthermore,  it  justifies  the  nursery- 
man in  propagating  from  the  nursery  row,  i.e.,  from  young  trees,  provided 
there  is  no  question  of  identity. 

In  General. — At  present  comparatively  little  is  known  as  to  the  extent 
of  bud  mutation  within  the  various  fruit  groups.  It  is  possible  that 
opinions  regarding  pedigreed  trees  may  need  revision.  Considering  the 
present  state  of  knowledge  the  prospective  purchaser  should  ascertain 
accurately  just  what  is  meant  by  the  term  "pedigreed"  stock  in  each 
case,  the  extent  to  which  such  nursery  stock  differs  from  the  ordinary  in  its 
source  and  in  its  later  performance  record.  Not  until  then  can  he  tell  how 
to  reckon  its  comparative  value. 

There  is  no  doubt  that  occasional  variations  occur  and  can  be  per- 
petuated, but  there  is  also  no  doubt  that  much  of  the  variation  between 
trees  in  the  same  orchard  is  due  to  soil  variations  or  to  differences  in 
stocks  and  that  these  variations  are  not  perpetuated.  The  fact  that  stock 
is  propagated  from  a  superior  individual  indicates  a  bare  possibility  that 
it  is  superior  but  it  does  not  establish  a  probability  that  it  is,  much  less 
a  certainty. 

Suggested  Collateral  Reading 

Webber,  H.  J.     Selection  of  Stocks  in  Citrus  Propagation.     Calif.  Agr.  Exp.  Sta. 

Bui.  317.     1920. 
Burbidge,   A.    F.    W.     The   Propagation   and   Improvement  of   Cultivated   Plants. 

Pp.  57-86.     London,  1877. 
Bonns,   W.  W.,  and  Mertz,   W.   M.     Experiments  with  Stocks  for  Citrus      Calif. 

Agr.  Exp.  Sta.  Bui.  267.     1916. 
Bioletti,  F.  T.     Grape  Culture  in  California.     Calif.  Agr.  Exp.  Sta.  Bui.  197.     1908. 
Bioletti,  F.  T.     Resistant  Vineyards.  Calif.  Agr.  Exp.  Sta.  Bui.  180.     1906. 


PROPAGATION  607 

Hedrick,  U.  P.  Grape  Stocks  for  American  Grapes.     N.  Y.  Agr.  Exp.  Sta.  Bui.  355. 

1912. 

Hatton,  R.  G.  Suggestions  for  the  Right  Selection  of  Apple  Stocks.     Jour.  Roy. 

Hort.  Soc.  45:  257-268.     1920. 

Literature  Cited 

1.  Allen,  W.  J.     New  South  Wales  Dept.  Agr.  Farmers'  Bui.  86.     1914. 

2.  Baco,  F.     Trav.  sci.  Univ.  Rennes.     10  (2):  88-90.     1911. 

3.  Ibid.     10  (2) :  97. 

4.  Ibid.     10  (2) :  152. 

5.  Ibid.     10  (2) :  158. 

6.  Ibid.     10  (2):  175. 

7.  Bailey,  L.  H.     Cornell  Univ.  Agr.  Exp.  Sta.  Bui.  71.     1894. 

8.  Bailey,  L.  H.     Stand.  Cycl.  Hort.     3:  1363.     New  York,  1917. 

9.  Bailey,  L.  H.     Nursery  Manual.     P.  167.     New  York,  1920. 

10.  Baltet,  C.     L'Art  de  Greffer.     P.  7.     Paris,  1902. 

11.  Ibid.     P.  119. 

12.  Ibid.     P.  211. 

13.  Ibid.     P.  369. 

14.  Ibid.     P.  415. 

15.  Ibid.     P.  453. 

16.  Barry,  P.     Horticulturist.     3:136.     1848. 

17.  Barry,  P.     The  Fruit  Garden.     P.  303.     Detroit,  1853 

18.  Ibid.     P.  310. 

19.  Barss,  H.  P.     Ore.  Agr.  Exp.  Sta.  Bienn.  Crop  Pest  and  Hort.  Rept.  1:213. 

1913 

20.  Berckmanns,  P.  J.     Proc.  Am.  Pom.  Soc.     P.  70.     1881. 

21.  Biffen,  R.  H.     Ann.  Bot.     16:  174.     1902. 

22.  Bioletti,  F.  T.     Cal.  Agr.  Exp.  Sta.  Bui.  197.     1908 

23.  Bioletti,  F.  T.     Cal.  Agr.  Exp.  Sta.  Bui.  180.     1906. 

24.  Bioletti,  F.  T.,  and  dal  Piaz,  A.  M.     Cal.  Agr.  Exp.  Sta.  Bui.  127.     1900. 

25.  Blunno,  M.     New  South  Wales  Dept.  Agr.  Farmers'  Bui.  80.     1914. 

26.  Bonus,  W.  W.,  and  Mertz,  W.  M.     Cal.  Agr.  Exp.  Sta.  Bui.  267.     1916. 

27.  Bradford,  F.  C.     Nat.  Nurseryman.     29:1.52.     1921. 

28.  Brown,  B.  S.     Modern  Propagation  of  Tree  Fruits.     P.  157.     New  York,  1916. 

29.  Ibid.     P.  160. 

30.  Brown,  W.  R.     Agr.  Res.  Inst.  Pusa  Bui.  93.     1920. 

31.  Budd,  J.  L.     la.  Hort.  Soc.  Proc.     14:  464.     1879. 

32.  Budd,  J.  L.     la.  Agr.  Exp.  Sta.  Bui.  10.     1890. 

33.  Burbidge,  F.  W.     Propagation  and  Improvement  of  Cultivated  Plants.     P.  59. 

London,  1877. 

34.  Ibid.     P.  60. 

35.  Ibid.     P.  69. 

36.  Ibid.     P.  264. 

37.  Ibid.     P.  267. 

38.  Cock,  S.  A.     Jour.  Dept.  Agr.  Victoria.     11:  372.     1913. 

39.  Ibid.     11:  714. 

40.  Cole,  C.  F.     Jour.  Dept.  Agr.  Victoria.     9.     1911. 

41.  Condit,  I.  J.     Cal.  Agr.  Exp.  Sta.  Bui.     250.     1915. 

42.  Corsa,  W.  P.     Nut  Culture  in  the  United  States.     P.  80.     Washington,  1896. 

43.  Coulter,  J.  L.,     Barnes,  C.  R.,  and  Cowles,  H.  C.     Text  Book  of  Botany.     2:777. 

New  York,  1911. 


608  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

44.  Ibid.     2:  779. 

45.  Crandall,  C.  S.     111.  Agr.  Exp.  Sta.  Bui.  211.     1918. 

46.  Cummings,  M.  B.     Vt.  Agr.  Exp.  Sta.  Bui.  221.     1921. 

47.  Cartel,  G.     Compt.  rend.     139:  491.     1904. 

48.  Daniel,  L.     Compt.  rend.     114:  1294.     1892. 

49.  Ibid.     136:  1157.     1903. 

50.  Daniel,  L.     Trav.  sci.  Univ.  Rennes.     2:  73.      1903. 

51.  Ibid.     2:  173. 

52.  Ibid.     2:  210. 

53.  Daniel,  L.     Rev.  hort.  10  (N.S.):  469.     1910. 

54.  Ibid.  13  (N.S.):  348.     1913. 

55.  Ibid.  14  (N.S.):  135.     1914. 

56.  Darwin,  C.     Animals  and  Plants  under  Domestication.     2:  266.     New  York. 

1894. 

57.  Dawson,  J.     Mass.  Hort.  Soc.  Trans.     P.  123.     1895. 

58.  Ibid.     P.  134. 

59.  Dental,  J.  B.     Rev.  hort.     16  (N.S.):  47.     1916. 

60.  Downing,  A.  J.     Fruits  and  Fruit  Trees  of  America.     P.  25.     New  York,   1856. 

61.  Diiplessix.  Trav.  sci.  Univ.  Rennes.      10  (2):  5.      1911. 

62.  Ibid.  10  (2):  18. 

63.  Ibid.  10  (2):  38. 

64.  Ibid.  10  (2):  192. 

65.  Gardner,  V.  R.     Mo.  Agr.  Exp.  Sta.  Res.  Bui.  39.     1920. 

66.  Gould,  H.  P.     U.  S.  D.  A.  Farmers'  Bui.  776.     1916. 

67.  Hansen,  N.  E.     S.  D.  Agr.  Exp.  Sta.  Bui.  87.     1904. 

68.  Hansen,  N.  E.     S.  D.  Agr.  Exp.  Sta.  Bui.  93.     1905. 

69.  Harwell,  R.     Horticulturist.     5:  257.     1850. 

70.  Hatton,  R.  G.     Jour.  Roy.  Hort.  Soc.     45  (2):  257.     1919-1920. 

71.  Ibid.  45  (2).     269. 

72.  Hedrick,  U.  P.     Plums  of  New  York.     P.  115.     Albany,  1911. 

73.  Hedrick,  U.  P.     N.  Y.  Agr.  Exp.  Sta.  Bui.  355.     1912. 

74.  Hedrick,  U.  P.     N.  Y.  Agr.  Exp.  Sta.  Cir.  18.     1912. 

75.  Hedrick,  U.  P.     N.  Y.  Agr.  Exp.  Sta.  Bui.  406.     1915. 

76.  Hedrick,  U.  P.     Cherries  of  New  York.     P.  72.     Albany,  1919. 

77.  Hendrickson,  A.  H.     Cal.  Sta.  Dept.  Agr.  Mo.  Bui.  4:  171-174.     1918. 

78.  Horticulturist.     6:337.     1851. 

79.  Ibid.     6:374. 

80.  Howard,  A.,  and  Howard,  G.  L.  C.     Sci.  Rept.  Agr.  Inst.  Pusa.     P.  48.     1916- 

1917. 

81.  Howard,  W.  L.     Cal.  Board  Hort.  Mo.  Bui.     9:  3.     1920. 

82.  Hume,  H.  H.     Fla.  Agr.  Exp.  Sta.  Bui.  71.     1904. 

83.  Husmann,  G.  C.     U  .S.  D.  A.,  Bur.  PI.  Ind.  Bui.  172.     1910. 

84.  Husmann,  G.  C.     U.  S.  D.  A.,  Bui.  856.     1920. 

85.  la.  Agr.  Exp.  Sta.  Ann.  Rept.     P.  33.     1919. 

86.  Jost,  L.     Pflanzenphysiologie.     3te.  Auflage.     P.  448.     Jena,  1913. 

87.  Kelly,  W.  P.,  and  Thomas,  E.  E.     Cal.  Agr.  Exp.  Sta.  Bui.  318.     1920. 

88.  Knight,  T.  A.     Phys.  and  Hort.  Papers.     P.  155.     London,  1841. 

89.  Ibid.     P.  223. 

90.  Ibid.     P.  273. 

91.  Ibid.     P.  274. 

92.  Laurent,  C.     Trav.  sci.  Univ.  Rennes.     8:  37.     1909. 

93.  Lawrence,  J.     Clergyman's  Recreation.     P.  64.     London,  1717. 

94.  Leclerc  du  Sablon.     Compt.  rend.  136:  623.     1903. 


PROPAGATION  609 

95.  Lindemuth,  H.     Landw.  Jahrb.     7:  909.     1878. 

96.  Ibid.     7:  912. 

97.  Lindemuth,  H.     Ber.  Bot.  Gesel.     19:  515.     1901. 

98.  Ibid.     19:  527. 

99.  Lindley,  J.     Theory  and  Practice  of  Horticulture.     P.  355.     London,  1855. 

100.  Livingstone,  J.     Trans.  Hort.  Soc.  London.     4:  231.     1822. 

101.  Loudon,  J.  C.     The  Horticulturist.     P.  283.     London,  1860. 

102.  Lucas,  E.     Die  Lehre  vom  Baumschnitt.     P.  37.     Ravensburg,  1874.     Cited  in 

Lindemuth,  H.,  Landw.  Jahrb.     7:  911.     1878. 

103.  Macdonald,  L.     Jour.  Dept.  Agr.  Victoria.     10:  69.     1912. 

104.  Macoun,  W.  T.     Cent.  (Can.)  Exp.  Farms.  Bui.  38.     1907. 

105.  Manning,  R.     Mass.  Hort.  Soc.  Trans.     P.  37.     1S79. 

106.  Mass.  Hort.  Soc.  Trans.     Pp.  6-43.     1879. 

107.  Maynard,  S.  T.     Hatch  (Mass.)  Agr.  Exp.  Sta.  Bui.  17.     1892. 

108.  Maynard,  S.  T.     Successful  Fruit  Culture.     P.  74.     New  York,  1909. 

109.  Ibid.     P.  197. 

110.  Mills,  J.  W.     Cal.  Agr.  Exp.  Sta.  Eul.  138.     1902. 

111.  Moore,  J.  G.     Proc.  Am.  Soc.  Hort.  Sci.     16:  84.     1919. 

112.  Murneek,  A.  L.     Better  Fruit.     15:  No.  7.     1921. 

113.  Neer,  F.  E.     Correspondence.     1921. 

114.  Noisette,   L.     Vollstand.    Handb.    der   Gartenkunst.    Uebersetzt   von    Sigwart. 

Stuttgart.     1826. 

115.  Oberdieck.     Illus.  Monatshefte  fiir  Obst-  und  Weinbau.     P.  44.      1873. 

Cited  by  Lindemuth,  H.,  Landw.  Jahrb.     7:  909.     1878. 

116.  Onderdonik,  G.     Proc.  Am.  Pom.  Soc.     P.  92.     1901. 

117.  Pepin.     Rev.  hort.     Ser.  3.     2:  183.     1848. 

118.  Proc.  Am.  Pom.  Soc.     1881. 

119.  Proc.  Am.  Pom.  Soc.     P.  128.     1889. 

120.  Reimer,  F.  C.     Ann.  Rept.  Pac.  Coast  Assoc.  Nurserymen.     1916. 

121.  Rivers,  T.     The  Miniature  Fruit  Garden.     P.  103.     New  York,  1866. 

122.  Riviere,  G.  et  Bailhache,  G.     Compt.  rend.     124:  477.     1897. 

123.  Roeding,  G.  C.     Fruit  Growers'  Guide.     P.  18.     Fresno,  1919. 

124.  Ibid.     P.  20. 

125.  Ibid.     P.  26. 

126.  Rolfs,  P.  H.     Fla.  Agr.  Exp.  Sta.  Bui.  127.     1915. 

127.  Sahut,  F.     Rev.  hort.  57:  149.     1885. 

128.  Ibid.  57:  201. 

129.  Ibid.    -57:  258. 

130.  Ibid.     57:  305. 

131.  Ibid.     57:  398. 

132.  Shamel,  A.  D.     et  al.     U.  S.  D.  A.,  Bui.  623.     1918. 

133.  Shamel,  A.  D.     et  al.     U.  S.  D.  A.,  Bui.  624.     1918. 

134.  Shaw,  J.  K.     Proc.  Am.  Soc.  Hort.  Sci.     14:  64.     1917. 

135.  vShaw,  J.  K.     Science.     45  (N.S.);  461.     1917. 

136.  Shaw,  J.  K.     Mass.  Agr.  Exp.  Sta.  Bui.  190.     1919. 

137.  vShaw,  J.  K.     Correspondence.     1921. 

138.  Sorauer,   P.     Manual  of  Plant  Diseases.     3d  ed.    (transl.)     1:  841.     Wilkes- 

barre,  1920. 

139.  Stuart,  W.     Vt.  Agr.  Exp.  Sta.  Ann.  Rept.     18:  300.     1905. 

140.  Swingle,  W.  T.     U.  S.  D.  A.,  Bur.  PI.  Ind.  Cir.  46.     1909. 

141.  Talbot,  J.     Mass.  Hort.  Soc.  Trans.     P.  6.     1879. 

142.  Taylor,  R.  H.     Cal.  Agr.  Exp.  Sta.  Bui.  297.     1918. 

143.  Tufts,  W.  P.     Correspondence.     1921. 


610  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

144.  Yard,  E.     Rev.  hort.     63:  514.     1891. 

145.  Victoria  Jour.  Dept.  Agr.     14:  6.     1916. 

146.  Voechting,  H.     Cited  by  Lindemuth,  H.     Ber.  Bot.  Gesel.     19:  515.     1901. 

147.  Vosbury,  E.  D.     U.  S.  D.  A.     Farmers'  Bui.  1122.     1920. 

148.  Waugh,  F.  A.     Vt.  Agr.  Exp.  Sta.  Ann.  Rept.     13:  333.     1900. 

149.  Waugh,  F.  A.     Vt.  Agr.  Exp.  Sta.  Ann.  Rept.     14:  259.     1901. 

150.  Waugh,  F.  A.     Plums  and  Plum  Culture.     P.  238.     New  York.     1910. 

151.  Webber,  H.  J.     Cal.  Agr.  Exp.  Sta.  Bui.  317.     1920. 

152.  Webber,  H.  J.  et  al.     Cal.  Agr.  Exp.  Sta.  Bui.  304.     1919. 

153.  Wickson,  E.  J.     California  Fruits.     P.  246.     San  Francisco.     1910. 

154.  Ibid.     P.  345. 

155.  Ibid.     P.  439. 

156.  Wisker,  A.  L.     Cal.  Board  Hort.  Mo.  Bui.     5:  112.     1916. 


SECTION  VII 
GEOGRAPHIC  INFLUENCES  IN  FRUIT  PRODUCTION 

Perseverance  has  not  only  developed  fruits  with  qualities  superior 
to  those  of  the  wild;  it  has  extended  their  growth  into  regions  to  which 
they  are  not  native.  The  two  most  important  orchard  fruits  of  the 
United  States  are  not  indigenous.  Social  and  economic  conditions  have 
played  no  unimportant  parts  in  developing  fruit  growing  or  in  preventing 
its  development.  Transportation  facilities  or  neighboring  markets  are 
of  utmost  importance.  Necessary  as  these  all  are,  however,  they  can 
not  estabhsh  a  fruit  growing  industry  unless  its  development  is  possible 
under  the  complex  of  natural  influences  which  are  grouped  conveniently 
under  the  term  geographic.  Though  complete  analysis  of  this  complex 
is  impossible,  since  one  factor's  influence  may  be  modified  by  that  of 
another  factor,  some  general  statements  can  be  made  with  safety. 

A  knowledge  of  the  conditions  which  favor,  interfere  with  or  prevent 
fruit  growing  at  various  points  may  be  of  considerable  value  for  local 
application,  since  it  may  suggest  the  capitalization  of  certain  features  of 
the  local  climate  through  the  growing  of  fruits  best  suited  to  those  condi- 
tions or  it  may  indicate  certain  departures  of  the  local  climate  from  the 
best  conditions  for  a  given  fruit,  necessitating  particular  care  in  some 
phase  of  management.  Furthermore,  it  may  suggest  to  the  plant  breeder 
definite  aims  in  improvement  to  secure  adaptation  or  possibly  it  may 
indicate  sources  of  material  with  which  he  can  work  most  profitably. 
Plant  improvement  for  one  section  may  be  quite  different  from  the 
amelioration  necessary  in  the  same  fruit  for  another. 


611 


CHAPTER  XXXIII 
THE   GEOGRAPHY  OF  FRUIT  GROWING 

Certain  fruits  like  the  apple  are  grown  throughout  most  of  the  tem- 
perate regions  of  both  hemispheres,  the  industry  in  the  case  of  the  apple 
reaching  its  height  in  the  northern  half  of  the  United  States  and  Europe 
and  in  the  southern  part  of  Australia,  Tasmania  and  New  Zealand.  The 
pear  is  cultivated  throughout  practically  the  same  range;  its  quantity 
production  is  much  more  localized.  Sweet  cherry  production  is  developed 
mainly  in  the  western  nations  of  Europe  and  the  western  states  of  North 
America.  None  of  these  fruits  is  of  great  importance  in  South  America, 
though  the  grape,  which  is  grown  along  with  the  apple  and  pear  in  North 
America,  Europe,  Asia  and  Australia  is  an  extremely  important  fruit 
on  that  continent.  On  the  other  hand,  certain  fruits  have  very  restricted 
geographic  ranges.  The  date  is  grown  mainly  in  countries  bordering  the 
Mediterranean,  the  jaboticaba  in  parts  of  Brazil,  the  jujube  in  central 
China,  the  pecan  in  the  southeastern  United  States,  the  loganberry  in 
Washington,  Oregon  and  California.  The  accompanying  maps  (Figs. 
59  to  64)  present  graphically  a  few  interesting  facts  regarding  the  geo- 
graphic distribution  of  certain  of  the  more  common  fruits.  Incidentally 
Figs.  59  and  60,  representing  total  apple  production  and  total  number  of 
apple  trees  of  bearing  age  in  the  United  States  in  1909,  show  that  actual 
production  is  often  not  proportional  to  ti'ee  number. 

The  distribution  of  individual  varieties  is  equally  interesting.  For 
instance  the  Fameuse  apple  is  of  great  importance  in  the  St.  Lawrence 
river  region,  the  Yellow  Bellflower  in  parts  of  California,  the  Huntsman 
in  Missouri;  Yellow  Newtown  is  important  in  New  York,  Virginia, 
Washington,  Oregon,  California,  Tasmania  and  New  South  Wales. 

It  is  one  thing  to  construct  a  map  which  shows  the  geographic  dis- 
tribution of  various  fruits;  it  is  quite  another  to  find  the  exact  reasons  for 
this  distribution.  Without  doubt  many  factors  are  operative.  Some 
are  of  relatively  great,  others  of  much  less,  importance.  A  single  factor 
may' be  decisive  with  one  fruit,  an  entirely  different  factor  with  another 
and  a  group  of  several  factors  may  be  of  almost  equal  importance  in  a 
third  case. 

LIFE  ZONES,  CROP  ZONES  AND  FRUIT  ZONES 

In  a  broad  way  the  fruit  zones  of  the  world  coincide  more  or  less  closely 
with  the  general  life  zones  and  crop  zones,  though  the  pomologist  may  use 

612 


THE  GEOGRAPHY  OF  FRUIT  GROWING 


613 


614 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


0^'Vr^-—~^ 

_^ 

V-,, 

& 

m*i~S\ 

r 

/  .'•'      ' '  (•     1  *  -•  ■ 

^ 

P 

fe/V^ 

\ 

\  'xZ-Htlir 

"  3 

NiYT~T^ 

'■.  ^ 

f> 

UNITED  STATES     \ 

)L 

J 

APPLES           Vr^ 

JV^^-^SAiS 

\ 

TREES  OF  BEARING  AGE 

\    r 

?     \ 

APPROXIMATE  ACREAGE 

\  { 

\     J 

EACH  DOT   REPRESENTS  500   ACRES 

^ 

V 

Fig. 


60. — Apple  trees  of  bearing  age,  approximate  acreage,  1910. 
Baker^) 


(After  Finch  and 


>■#  \'--'/77"""^~"~---_ 

.     i> 

4^ 

\      -^     1         ^■~~-^>^     / 

\^A 

?^^-^ 

W\   pl — ^lZ 

W 

^M 

y\ 

1  V^ 

\j  :    /^~~~"    U 

ZXj 

r^^r 

UNITED  STATEsV 

PEARS                Vr-x 

TREES  OF  BEARING  AND                 \ 
NOT  OF  BEARING  AGE                        \ 
APPROXIMATE  ACREAGE                                      \ 

iL 

^ 

EACH    DOT   REPRESENTS  100  ACRES 

y^ 

Fig.  61. 


-Approximate  acreage  of  pear  trees  in  the  United  States.      (After  Finch  i 
Baker^) 


THE  GEOGRAPHY  OF  FRUIT  GROWING 


615 


616 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


THE  GEOGRAPHY  OF  FRUIT  GROWING 


617 


other  names  to  designate  them  than  the  biological  cartographer  does. 

These  general  life  zones  as  determined  for  the  United  States,  southern 

Canada  and   northern   Mexico 

by    the    Bureau   of    Biological 

Survey    of   the    United   States 

Department  of  Agriculture,  are 

shown  in  Fig.  65. 

The  Boreal  Zone. — As  here 
outlined,  the  Boreal  zone  or 
region  includes  all  of  Canada 
except  a  portion  of  Nova 
Scotia,  a  strip  along  the  St. 
Lawrence  River  and  running 
west  through  Ontario  to  Lake 
Huron  and  Georgian  Bay, 
southern  Saskatchewan  and 
limited  areas  in  southern 
Manitoba,  Alberta  and  British 
Columbia.  Its  southern  boun- 
dary dips  down  into  the  United 
States  so  as  to  include  parts  of 
northern  New  England,  north- 
ern Michigan,  a  small  strip  of 
northeastern  Wisconsin  and  a 
considerable  part  of  Minnesota 
and  North  Dakota.  Irregular- 
ly shaped  areas  characterized 
by  the  life  of  the  Boreal  region 
are  found  here  and  there  in 
New  York  and  Pennsylvania 
and  at  some  of  the  higher  eleva- 
tions of  the  Allegheny  Moun- 
tains as  far  south  as  southern 
Tennessee.  In  the  western 
parts  of  the  United  States 
there  are  finger-like  projections 
of  this  region  and  isolated  areas 
with  its  characteristic  fauna 
and  flora  extending  as  far  south 
as  the  state  of  Zacatecas  in 
Mexico.  For  the  most  part  these  extreme  southern  extensions  are  Hmited 
to  the  higher  elevations  of  the  Rocky,  Sierra  Nevada,  Cascade  and  Coast 
mountain  ranges.  Its  southern  limit  is  marked  by  the  isotherm  of  18°C. 
(64.4°F.)  for  the  six  hottest  consecutive  weeks  of  midsummer. ^^     On  the 


618 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


whole  this  region  is  not  suited  to  fruit  growing;  nevertheless  a  number  of 
fruits  are  thoroughly  at  home  and  indeed  reach  their  best  development 


along  its  southern  borders.     Among  these  arc  the  cranberry,  blueberry, 
currant  and  gooseberry. 


THE  GEOGRAPHY  OF  FRUIT  GROWING  619 

The  Tropical  Zone. — Only  a  very  small  part  of  the  continental  United 
States  is  included  within  the  Tropical  region  or  zone.  To  be  exact,  there 
are  three  widely  separated  areas  where  tropical  conditions  prevail  and 
tropical  vegetation  abounds — one  in  southern  Florida,  one  in  extreme 
southeastern  Texas,  and  one  along  the  California-Arizona  line,  extending 
as  far  north  as  southern  Nevada.  Within  these  areas  are  such  fruits  as 
the  banana,  pineapple,  mango,  date  palm,  cocoanut,  papaya  and  cheri- 
moya.  This  region  is  never  visited  by  frosts  or  freezing  temperatures  and 
many  of  the  fruits  grown  in  it  are  said  to  be  seriously  injured  by  tempera- 
tures even  closely  approaching  the  freezing  point.  To  the  pomologist, 
as  to  the  biologist,  this  region  is  known  as  the  Tropical  zone.  It  is  char- 
acterized by  having  more  than  14,400°C.  (26,000°F.)  of  heat  during  the 
year — degrees  of  normal  mean  daily  heat  in  excess  of  a  minimum  of  6°C. 
(43°F.),*^  which  is  rather  arbitrarily  assumed  as  marking  the  inception 
of  physiological  activity  in  plants. 

Austral  or  Temperate  Zone. — Between  the  Boreal  region  on  the  north 
and  the  Tropical  region  on  the  south  and  embracing  most  of  the  area  of  the 
United  States,  is  a  region  designated  as  Austral  on  the  maps  of  biological 
surveys  and  designated  as  the  Temperate  zone  by  the  pomologist.  Frosts 
and  freezes  are  likely  to  occur  throughout  most  of  this  region,  but  mini- 
mum winter  temperatures  seldom  go  below  —  30°F.  at  the  north  and  the 
mean  temperature  of  midwinter  months  even  of  the  more  northern 
sections  is  well  above  zero. 

Transition  Zone. — Biologists  recognize  three  transcontinental  life 
zones  within  this  region,  a  so-called  Transition  zone  to  the  north  and  an 
Upper  Austral  and  Lower  Austral  zone  to  the  south.  Some  of  the  more 
hardy  fruits,  as  the  apple,  pear,  red  raspberry  and  the  Nigra  and  European 
groups  of  plums  find  their  most  congenial  home  in  the  Transition  zone. 
In  the  east  this  zone  includes  most  of  those  portions  of  New  England, 
New  York,  Pennsylvania  and  Michigan  and  in  the  middle  west  most  of 
those  portions  of  Wisconsin,  Minnesota  and  the  Dakotas  not  included 
in  the  Boreal  region;  in  the  west  it  includes  many  irregularly  shaped 
areas  from  the  Canadian  border  to  Mexico,  and  even  in  Mexico,  where 
elevation  causes  comparatively  low  temperatures.  "Transition  zone 
species",  Merriam  states,  ''require  a  total  quantity  of  heat  of  at  least 
5500°C.  (10,000°F.)  but  can  not  endure  a  summer  temperature  the  mean 
of  which  for  the  six  hottest  weeks  exceeds  22°C.  (71.6°F.)  The  northern 
boundary  of  the  Transition  zone,  therefore,  is  marked  by  the  isotherm 
showing  a  sum  of  normal  positive  temperatures  of  5,500°C.  (10,000°F.), 
while  its  southern  boundary  is  coincident  with  the  isotherm  of  22°C. 
(71.6°F.)  for  the  six  hottest  consecutive  weeks. "''^ 

This  Transition  zone  is  in  turn  divided  into  three  areas  by  lines  having 
a  general  north  and  south  direction,  areas  that  differ  from  one  another 
primarily   in   rainfall   and   atmospheric   humidity.     The   eastern   area, 


620  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

known  as  the  Alleghanian,  extends  from  the  Atlantic  seaboard  approxi- 
mately to  the  100°  meridian,  which  runs  through  central  North  and  South 
Dakota,  Nebraska  and  Texas.  To  the  west  of  this  is  a  central  arid  area 
extending  to  the  Sierra  Nevada-Cascade  mountain  range.  West  of  this 
is  the  Pacific  coast  humid  area,  very  humid  at  the  north  but  toward  the 
south  gradually  merging  into  the  conditions  presented  by  the  central 
arid  area.  Generally  speaking,  the  same  fruit  species  thrive  in  all  of  these 
areas,  though  they  cannot  be  grown  without  irrigation  in  the  central 
arid  section.  However,  though  the  same  fruit  species  are  grown  in  all 
three  areas  the  same  varieties  are  not  equally  successful;  consequently 
each  area  has  a  more  or  less  distinctive  variety  flora. 

Upper  Austral  Zone. — The  Upper  Austral  region  includes  a  compara- 
tively narrow  belt  of  territory  in  the  central  Atlantic  States  but  widens 
out  to  include  a  comparatively  large  part  of  the  corn  belt  area  in  the 
middle  west  and  like  the  Boreal  and  Transition  regions  it  includes  many 
irregularly  shaped  areas  from  the  Canadian  line  to  far  below  the  Mexican 
border.  According  to  Merriam:  "Upper  Austral  species  require  a  total 
quantity  of  heat  of  at  least  6,400°C.  (11,500°F.),  but  apparently  cannot 
endure  a  summer  temperature  the  mean  of  which  for  the  six  hottest 
consecutive  weeks  exceeds  26°C.  (78.8°F.).  The  northern  boundary  of 
the  Upper  Austral  zone,  therefore,  is  marked  by  the  isotherm  showing  a 
sum  of  normal  positive  temperatures  of  6400°C.  (11,511°F.)  while  its 
southern  boundary  agrees  very  closely  with  the  isotherm  of  26°C. 
(78.8°F.)  for  the  six  hottest  weeks. "*^  The  eastern  half  of  this  zone, 
known  as  the  Carolinian  area,  has  a  humid  climate;  the  western  half, 
known  as  the  Upper  Sonoran  area,  is  comparatively  arid.  The  walnut, 
hickory,  sassafras,  sycamore,  red  bud  and  papaw  are  typical  native 
trees  of  the  Carohnian  area;  the  sage  brush,  grease  wood  and  juniper 
characterize  the  Upper  Sonoran.  Within  this  zone  the  peach,  the 
Japanese  plum,  the  persimmon  and  many  varieties  of  the  apple,  pear, 
cherry  and  grape  attain  their  highest  development. 

Lower  Austral  or  Subtropic  Zone. — The  Lower  Austral  zone  lies 
between  the  Upper  Austral  and  Tropical  regions.  On  the  east  it  includes 
most  of  the  south  Atlantic  seaboard  and  in  the  Mississippi  valley  it 
extends  north  into  southern  Missouri,  Ilhnois  and  Indiana;  in  the  west 
it  includes  most  of  southern  California  and  much  of  the  Sacramento  and 
San  Joaquin  valleys.  Merriam  states:  "Lower  Austral  species  require  a 
total  quantity  of  heat. of  at  least  10,000°C.  (18,000°F.).'"»5  Like  the 
Upper  Austral  zone,  its  eastern  half  has  a  humid  and  its  western  half  an 
arid  climate.  The  eastern  half  is  known  as  the  Austroriparian  area,  the 
western  half  as  the  Lower  Sonoran.  The  former  is  characterized  by  such 
native  vegetation  as  the  long-leaf  and  loblolly  pines,  the  magnolia,  the 
Hve  oak  and  the  pecan.  It  is  a  rich  agricultural  area  producing  cotton, 
rice,  sugar  cane  and  many  other  warm  season  crops.     The  distinctive 


THE  GEOGRAPHY  OF  FRUIT  GROWING  621 

fruits  of  its  more  northern  reaches  are  the  pecan,  the  muscadine  grapes 
and  pears  of  the  oriental  hybrid  class.  The  Lower  Sonoran  area  is 
characterized  by  many  cacti,  yuccas,  agaves,  mesquites  and  other  desert 
plants.  It  produces  plums,  prunes,  peaches,  cherries,  apricots,  almonds, 
grapes  and  many  other  fruits  in  great  quantities  where  irrigation  water  is 
available.  The  southern  part  of  the  Lower  Austral  zone  is  known  to  the 
pomologist  as  the  Subtropic  zone.  Horticulturally  it  is  one  of  the  most 
important  in  the  United  States.  Within  it  are  produced  citrus  fruits, 
figs,  avocados,  loquats,  Japanese  persimmons  and  many  other  less 
known  fruits. 

Attention  may  be  directed  to  the  fact  that  the  boundaries  of  the 
pomological  districts  of  the  United  States,  as  they  have  been  mapped  by 
the  American  Pomological  Society  do  not  coincide  exactly  with  those  of 
the  life  zones  that  have  been  discussed,  though  the  two  maps  have  many 
features  in  common. 


GEOGRAPHY  OF  FRUIT  PRODUCTION  AS  INFLUENCED  BY  TEMPERATURE 

It  will  be  noted  that  these  life  zones  or  crop  zones  include  areas  charac- 
terized by  a  certain  uniformity  of  climate  and  that,  of  all  the  features 
that  constitute  climate,  temperature  is  given  first  consideration.  Indeed 
the  boundaries  of  the  different  regions  and  zones  are  for  the  most  part 
isothermals,  and  the  main  reason  for  such  irregular  outlines,  especially 
in  the  mountainous  districts,  is  the  influence  of  altitude  upon  temperature. 
High  altitude  through  its  accompaniment  low-temperatur,  accounts  for 
the  island-like  areas  of  the  Boreal  or  Transition  zones  in  latitudes  gen- 
erally dominated  by  the  life  of  the  Austral.  Generally  there  is  a  lower- 
ing of  about  4°F.  in  mean  temperature  for  each  increase  in  elevation 
of  1,000  feet.  Even  at  the  equator  frost  will  occur  at  an  elevation  of 
about  18,000  feet;  on  the  island  of  Hawaii,  at  a  latitude  of  20°  North, 
frost  occurs  at  an  altitude  of  4,500  feet  or  above. ''^ 

Temperature  here  is  meant  to  include  •  not  only  the  mean  annual 
temperature  but  also  the  minimum  and  maximum  temperatures  of 
winter,  spring,  summer  and  autumn,  respectively,  the  mean  temperature 
month  by  month,  particularly  through  the  growing  season,  the  occurrence 
of  frost  during  the  critical  period  just  before,  during  and  just  after, 
blossoming,  the  length  of  the  growing  season  (see  Fig.  66),  the  evenness 
of  temperature  from  day  to  day,  and  many  other  characteristics  of  the 
weather  that  are  more  or  less  directly  attributable  to  temperature 
changes.  Sometimes  it  is  one  of  these  features  of  temperature,  e.g., 
minimum  winter  temperature,  or  mean  temperature  during  the  growing 
season,  that  sets  the  limits  for  a  certain  fruit;  sometimes  it  is  another. 
Broadly  speaking  it  is  the  minimum  winter  temperatures  that  set  northern 


622 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


limits  to  the  production  of  fruits  of  particular  kinds  and  mean  rather  than 
maximum  temperatures  during  four  to  six  weeks  of  the  warmest  weather, 
that  set  their  southern  limits. ^^  There  are,  however,  numerous 
exceptions. 


Fig.  66. — Computed  length  of  available  growing  season  4  years  in  5.     (After  R^ 


Peach  Growing  as  Influenced  by  Temperature. — The  varying  in- 
fluences of  temperature  on  the  geographic  range  of  fruits  are  shown 
clearly  by  the  peach,  if  comparison  be  made  between  Europe  and  the 
United  States.  Table  1  shows  mean  monthly  temperatures  at  selected 
points.  Bordeaux,  Perpignan,  Montpelher  and  Lyons  in  France  may  be 
considered  to  have  temperatures  favorable  to  peach  growing.  Roscoff, 
in  Brittany,  Plymouth,  England,  and  Bergen,  Norway,  are  in  regions 
where  few  or  no  peaches  are  grown,  though  they  are  warmer  in  winter  than 
Rochester,  New  York,  which  is  typical  of  much  of  the  peach-growing  area 
in  the  northeastern  states.  The  difference  between  the  points  named 
where  peach  growing  is  successful  and  those  where  it  is  not  Hes  in  the  sum- 
mer temperatures.  So  far  as  winter  temperature  is  concerned  peaches 
apparently  could  be  grown  in  Berufjord,  Iceland;  deficiency  in  summer 
temperatures  seems  the  limiting  factor  in  a  considerable  part  of 
Europe. 

Between  Nashua  and  Concord,  in  New  Hampshire,  about  35  miles 
apart,  runs  the  northern  limit  of  commercial  peach  growing  in  that  section. 
Examination  of  the  table  shows  only  small  differences  in  mean  monthly 


THE  GEOGRAPHY  OF  FRUIT  GROWING  623 

temperatures;  the  absolute  minima  for  the  two  stations  are,  respectively, 
—  25°F.  and  — 35°F.  Near  the  one  point  commercial  peach  growing  is 
profitable;  a  few  miles  away  it  becomes  unprofitable.  The  July  tempera- 
ture for  Concord  is  identical  with  that  for  Fitchburg,  Mass.  (c/.  Table 
3),  well  within  the  zone  of  peach  growing,  and  greater  than  that  of 
Roseburg,  Ore.  Apparently,  then,  for  conditions  obtaining  in  southern 
New  Hampshire,  the  northern  limit  of  commercial  peach  production  is 
set  by  winter  temperatures  averaging  between  those  for  the  two  stations 
given. 

Pierre,  S.  D.,  has  as  high  or  higher  summer  temperatures  than  many 
sections  where  the  peach  grows  readily,  but  its  winter  temperatures  are 
too  low.  Near  Portland,  Maine,  the  peach  reaches  its  limit  in  ordinary 
cultivation  and  is  subject  to  winter  injury.  Portland,  Ore.,  with  a  summer 
temperature  slightly  lower,  provides,  through  milder  winters,  conditions 
such  that  the  peach  grows  fairly  well.  Near  Lincoln,  Neb.,  the  peach 
grows  about  as  at  Portland,  Maine;  though  the  winter  temperature 
averages  a  shade  lower,  the  summer  is  warmer,  suggesting  a  greater 
maturity  in  the  fall  with  consequent  ability  better  to  withstand  the  winter. 
This,  however,  is  the  only  waj'-  in  which  summer  temperature  may  be 
considered  to  influence  peach  growing  in  any  large  area  of  the  United 
States.  The  chief  limiting  temperature  factor  here  comes  in  the  winter. 
Nevertheless  the  factor  of  summer  temperature  or  the  length  of  the  grow- 
ing season  may  become  important  in  isolated  areas  along  the  northern 
border  of  peach  growing. 

Grape  Growing  as  Influenced  by  Temperature. — The  northern  limit 
of  grape  culture,  as  with  the  peach,  is  set  by  summer  temperatures  at 
some  points  and  by  winter  temperatures  at  others.  Its  course  in  Europe 
has  been  defined  as  extending  "from  somewhat  north  of  the  mouth  of  the 
Loire,  where  the  Marne  empties  into  the  Seine,  to  the  junction  of  the  Aar 
and  the  Rhine,  north  of  the  Erzgebirge,  to  about  the  52°  of  latitude, 
descends  along  the  Carpathians  to  the  49°,  extends  on  this  parallel  east- 
ward, and  near  the  Volga  turns  southward  to  its  mouth,  in  the  Caspian 
Sea."ii 

Wine  in  considerable  quantities  was  made  north  of  this  line,  in  Eng- 
land, and  even  in  Zeeland,  in  former  times.  This  fact,  sometimes  cited 
as  proving  a  change  in  climate  probably  proves  no  more  than  a  change  in 
taste.  "  It  must  be  taken  for  granted  that  in  those  times  when  there  was 
no  communication  over  long  distances  they  were  not  very  exacting  in 
regard  to  wine,  particularly  as  the  best  wines  were  unknown,  as  must 
have  been  the  case  in  northern  Germany,  the  Netherlands  and  England. 
If  the  wine  was  harsh  and  sour,  it  was  still  wine.  .  .  .  With  the 
present  facilities  for  communication  and  the  competition  in  the  wine 
business  resulting  therefrom;  vine  culture  is  no  longer  profitable  in  many 
places  where  30  years  ago  it  was  so;  .    .    ." 


624 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


The  boundary  thus  set,  therefore,  is  not  necessarily  the  Hmit  of  the 
abihty  of  the  grape  to  grow;  it  does,  however,  mark  the  Hmit  of  its  abihty 
to  ripen  sufficiently  for  wine  making.  This  line  in  western  Europe  is  set 
by  summer  temperatures.  In  eastern  Europe  it  is  set  by  winter  tem- 
peratures and  does  represent  approximately  the  real  limit  of  culture  of 
the  vine. 

Table  2  shows  the  mean  monthly  temperatures  for  a  number  of  selected 
European  stations.  Some  of  these,  for  example,  Bordeaux  in  France, 
Florence  in  Italy,  Patras  in  Greece  and  Odessa  in  Russia,  are  either  centers 
of  important  viticultural  industries  or  they  fairly  represent  such  districts. 
Others,  like  Bergen  in  Norway,  Plymouth  in  England  and  Roscoff  in  Brit- 
tany are  places  where  outdoor  grape  culture  for  wine  is  impracticable. 


Table  1.- 


-Mean  Monthly  Temperatures  in  Relation  to  Peach  Growing 
(Degrees  Fahrenheit) 


Bordeaux,  France  (1)  . 
Perpignan,  France  (1)  . 
Montpellier,  France  (1) 
Roscoff,  France  (1).  .  .  . 
Plymouth,  England  (1) 
Bergen,  Norway  (1)  .  . 
Lyons,  France  (1)  .  .  .  . 
Berufjord,  Iceland  (1)  . 

Concord,  N.  H.  (2) 

Nashua,  N.  H.  (2) 

Rochester,  N.  Y.  (3)  .. 
Portland,  Maine  (3)  .  . 
Portland,  Ore.  (3)    .  .  .  . 

Pierre,  S.  D.  (3) 

Lincoln,  Neb.  (3)    


1.  Hann.  J.,  Handb.  der  Klimatologie,  Stuttgart  (1911). 

2.  United  States  Department  Agriculture,  Weather  Bureau,  Bui.  Q.  (1906). 

3.  United  States  Department  Agriculture,  Weather  Bureau,  Bui.  R.  (1908). 

Yet  these  latter  points  have  mean  winter  temperatures  above  those  of 
some  of  the  grape  growing  districts  and  their  absolute  minimum  tempera- 
tures are  likewise  higher.  However,  their  mean  summer  temperatures  are 
comparatively  low — too  low  for  the  grape  to  mature  its  fruit  and  wood 
properly;  consequently  the  industry  does  not  flourish  there. 

Temperature  and  the  Geographic  Range  of  Apple  Varieties. — The 
same  general  principles  operate  to  establish  limits  for  the  profitable 
culture  of  different  varieties  of  the  same  fruit.  Thus,  winter  tempera- 
tures at  Eastport,  Maine,  are  higher  than  those  at  Lewiston,  in  the  same 
state.  The  Baldwin  apple  grows  very  well  around  Lewiston  but  not  at 
Eastport.     The  difference  in  suitability  of  the  two  places  hes  evidently 


THE  GEOaRAPHY  OF  FRUIT  GROWING  625 

in  the  summer  temperatures.  Madison,  Wis.,  has  evidently  sufficient 
summer  heat  to  satisfy  the  Baldwin's  requirements;  the  difficulty  in 
growing  Baldwin  at  this  last  point  is  known  to  be  winter  temperature. 
So  far  as  apple  growing  in  the  United  States  is  concerned,  then,  there 
are  along  the  northern  limit,  two  different  factors  operating,  summer 
temperature  and  winter  temperature;  the  effects  of  the  one  sometimes 
mask  those  of  the  other.  However,  there  appear  to  be  very  few  places 
listed  in  the  table  where  the  Baldwin  apple  would  suffer  from  lack  of 
summer  heat.  Data  are  presented  in  Tables  3  and  4  showing  the  mean 
monthly  temperatures  throughout  the  year  and  the  minimum  tempera- 
tures for  the  six  winter  months  at  a  number  of  stations  in  the  United 
States.  Except  for  the  California  and  Alaska  points,  each  station 
included  in  the  tables  may  be  taken  as  representing  fairly  well  a  commer- 
cial apple  producing  section.  The  figures  afford  an  idea  of  the  range  in 
mean  and  minimum  temperatures  within  which  apple  growing  is  profi- 
table and  by  inference,  an  idea  of  the  temperature  limits  for  the  commer- 
cial varieties.  A  comparison  of  these  data  with  the  records  of  the 
leading  varieties  in  the  several  districts  represented,  likewise  affords  a 
fairly  accurate  measure  of  their  particular  temperature  requirements 
and  this,  in  turn,  may  be  used  as  a  basis  for  judging  their  probable 
suitability  for  sections  where  they  have  not  been  tried  but  where  tem- 
perature records  are  available. 

Averages  are  treacherous  at  times  and  caution  should  be  observed 
in  their  interpretation.  Lewiston,  Maine,  shows  the  lowest  mean  winter 
temperatures  of  any  of  the  apple  sections  represented  in  Table  3.  Never- 
theless this  region  grows  successfully  several  apple  varieties  which  cannot 
be  grown  in  the  Bitter  Root  valley,  as  represented  by  Missoula.  Refer- 
ence to  Table  4  shows  that  the  mean  temperatures  for  Missoula  conceal 
a  November  minimum  of  —  20°F.  as  compared  with  plus  2°F.  for  Lewiston 
and  a  January  minimum  of  —  42°F.  for  Missoula  as  compared  with 
—  24°F.  for  Lewiston.  Over  a  long  period  the  amount  of  winter  killing 
around  Lewiston  is  probably  no  greater  than  that  around  Spokane,  Wash., 
though  Lewiston  averages  8°  colder  in  January  and  10°  colder  in  February. 
The  October  and  November  means,  however,  are  only  1°  apart.  Abso- 
lute minima  for  Lewiston  in  October,  November  and  January  are  actually 
higher  than  those  for  Spokane  (6°,  15°  and  6°F.  respectively).  The 
November  temperatures,  mean  and  minimum,  seem  particularly  impor- 
tant in  relation  to  winter  injury  along  the  northern  border  of  apple 
growing. 

The  total  effective  growing  temperatures  at  Portland,  Oregon,  and 
Portland,  Maine,  are  practically  the  same  and  the  same  varieties  of 
apples  attain  an  almost  equal  development  in  the  two  places.  Appar- 
ently in  this  case  neither  maximum  nor  mean  summer  temperatures  in 
Oregon  nor  minimum  winter  temperatures  in  Maine  are  limiting  factors 

40 


626  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

in  the  growth  of  the  varieties  in  question.  Mean  temperature  during 
the  growing  season,  therefore,  in  this  case  becomes  an  accurate  index  of 
adaptation  to  chmate. 

On  the  other  hand  the  loganberry  and  sweet  cherry  which  thrive  so 
well  in  the  vicinity  of  Portland,  Ore.,  cannot  be  grown  profitably  near 
Portland,  Maine,  because  minimum  winter  temperature  is  a  hmiting 
factor.  The  blueberry,  which  grows  so  luxuriantly  near  Portland,  Maine, 
fails  to  grow  near  Portland,  Ore.,  not  because  temperature  is  a  limiting 
factor  but  presumably  because  it  does  not  find  a  congenial  soil. 

Investigations  in  fruit  growing  at  Sitka,  Alaska,  show  interesting  effects  of 
a  rather  unusual  chmate.  From  November  to  March  inclusive  the  mean  tem- 
peratures are  higher  than  those  of  Lewiston,  Maine;  they  exceed  those  of  Roches- 
ter, N.  Y.,  for  nearly  the  same  period  and  for  December  to  February  they  are 
somewhat  higher  than  those  of  Martinsburg,  W.  Va.  Zero  temperatures  are 
very  rare;  nevertheless  winter  killing  is  common.  Records  of  the  Alaska  Agri- 
cultural Experiment  Stations  show  that  such  hardy  plums  as  De  Soto  and  RoU- 
ingstone,  numerous  apple  varieties  selected  for  hardiness,  the  sand  cherry  and 
blackberries  have  suffered  considerable  injury. 

The  causes  of  this  condition  are  indicated  in  the  following  quotations  from 
reports  of  the  station: 

"Only  early  maturing  sorts  will  succeed.  Varieties  which  are  summer 
apples  in  the  States  will  be  fall  apples  in  Alaska,  and  those  which  are  fall  apples 
in  the  States  will  not  mature  at  all  in  Alaska.  The  summer  heat  is  not  great 
enough.  In  the  coast  region  the  season  between  frosts  is  long — longer,  indeed, 
by  at  least  two  months  than  in  the  northern  tier  of  states. 

"In  the  larger  portion  of  the  coast  region  there  is  little,  if  any,  damaging  frost 
between  May  1  and  October  1,  and  some  seasons  damaging  frosts  do  not  occur 
until  the  end  of  October.  The  drawback  to  the  climate  in  this  region  hes  not 
in  too  great  cold,  but,  anomalous  as  the  statement  seems,  in  the  lack  of  summer 
heat.  .  .  .  The  maximum  temperature  is  more  generally  between  60°  and  70°, 
and  some  summers  it  will  not  go  much  above  60°.  In  the  interior,  on  the  other 
hand,  the  summers  are  warm  enough,  at  least  in  places  but  the  season  is  too 
short  to  hope  to  mature  any  but  the  earliest  sorts  and  there  is  considerable  doubt 
if  they  will  succeed."" 

"The  excessive  rainfall  and  continuous  mild  weather  prolongs  the  growing 
season  until  long  into  October.  The  young  wood  is  soft  and  succulent,  and 
moderately  cold  weather  the  following  winter  kills  it."^* 

"The  winter  of  1908-1909  was  quite  severe  for  this  part  of  the  coast  region. 
The  temperature  fell  to  2°  above  zero  and  3°  above  zero  in  January  and  Febru- 
ary, respectively,  and  the  cold  period  was  protracted  over  many  weeks.  As  a 
consequence,  the  young  growth  produced  in  the  season  of  1908  was  partly  killed 
in  most  cases,  and  in  some  cases  entirely. "^"^ 

"Blackberries  and  dewberries  cannot  be  grown  successfully  in  any  part  of 
Alaska.  They  have  been  tried  repeatedly  at  the  Sitka  Experiment  Station  and 
the  attempt  has  always  resulted  in  failure.  The  summer  is  not  warm  enough  to 
develop  the  fruit  and  the  plants  usually  winterkill  even  in  mild  winters,  probably 
due  to  the  late  succulent  growth  resulting  from  the  abundance  of  moisture."^® 


THE  GEOGRAPHY  OF  FRUIT  GROWING 


627 


Phenological  data  taken  at  Sitka  are  interesting.     Apples  are  recorded  as 
leafing  out  June  1;  Early  Richmond  cherry  in  blossom  June  15,  the  Whitney 

Table  2. — Mean  Monthly  Temperature  at  Selected  European  Stations 
(Cornp iled  fro m  Ha nn^^) 
(In  degrees  Fahrenheit) 


Bordeaux,  France . . 
Budapest,  Hungary 
Patras,  Greece  .  .  .  . 
Bremen,  Germany. 
Plymouth,  England 
Lemburg,  Austria.  . 
Roscoff ,  France .... 
Bergen,  Norway  .  .  . 

Florence,  Italy 

Nantes,  France 

Odessa,  Russia 


40.6 
2 
51.1 
33.6 
42.  1 
24.3 
45.0 
34.2 
40.7 
40.  1 
25.3 


42.9 
31.4 
53.0 
34.7 
42.8 
25.7 
44.8 
33.6 
42.1 
41.9 
27.7' 


46.9 
39.9 
56.1 
38.1 
43.8 
31.1 
46.2 
42.1 
48.9 
45.2 
34.9 


53.0 
51.  1 
61.  1 
46.0 
48.0 
46.2 
50.0 
48.9 
56.1 

;i.3 


68.2 
70.5 
80.8 
63.1 
61.0 
66.4 
61.3 
55.7 
76.1 
65.7 
47.  5  59.  2168.0  72.  5 


.3 
.  1 

67.8 
54.  1 
52.9 
57.0 
53.4 
55.1 
63.1 
56.3 


64.2 
66.7 
74.5 
60.3 
58.4 
64.3 
57.7 
55.2 
70.7 
62.2 


63.7 
61.1 
76.6 
56.5 
57.6 
57.0 
59.4 
50.7 
68.6 
60.4 
62.1 


.446.941.2 
.  1  40.2|30.6 


.861.1 
.4139.4 
1  46.8 

;34.7 

49.3 
138.5 
;49.3 


53.6 
35.1 
43.2 
27.2 
45.8 
34.7 
42.6 


45.3  40.6 

41.0'30.2 


Table  3. — Mean  Temperatures  of  Selected  Stations 
{Compiled  from  United  States  Weather  Bureau  Bui.  Q) 
(Degrees  Fahrenheit) 


Lewiston,  Maine.  .  .  . 
Fitchburg,  Mass. .    .  . 

Rochester,  N.  Y 

Albany,  N.  Y 

Vineland,  N.  J 

Charlottesville,  Va. . . 
Martinsburg,  W.  Va. 
Waynesville,  N.  C. . . 

Clayton,  Ga 

Marietta,  Ohio 

Griggsville,  111 

Springfield,  Mo 

Montrose,  Colo 

Provo,  Utah 

Missoula,  Mont 

Payette,  Idaho 

The  Dalles.  Ore 

Albany,  Ore 

Roseburg,  Ore 

Spokane,  Wash 

Moxee  Wells,  Wash.. 
Walla  Walla,  Wash. . 

Sacramento,  Cal 

Fresno,  Cal 

Los  Angeles,     Cal.... 

RosweU,  N.  M 

Sitka,  Alaska 


628 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


apnle  on  June  20.  Early  Richmond  cherries  and  Champion  gooseberries  were 
ripe  August  15;  the  Cuthbert  raspberry  usually  ripens  during  the  last  of  August. 
These  dates  explain  the  ability  of  only  a  few  apple  varieties  to  mature  fruit  there, 
the  most  satisfactory  being  Yellow  Transparent  and  Livland  Raspberry.  Pat- 
ten Greening  has  set  good  crops  but  failed  to  ripen  its  fruit. 

On  the  other  hand,  gooseberries,  currants  and  red  raspberries  thrive  at  this 
point  and  bear  heavily.  At  the  Kenai  Station,  where  repeated  efforts  failed  to 
produce  grain  crops  because  of  the  cool  summers,  these  fruits  were  satisfactory." 
Evidently  then,  though  these  fruits  endure  less  heat  and  drought  than  grain 
they  endure  more  rain  and  low  growing  season  temperatures.  Their  growing 
season  requirements  appear  to  resemble  those  of  cabbage  and  potatoes. 


Table  4. — Absolute  Minimum  Temperatures  op  Selected  Stations 

{Compiled  from  United  States  Weather  Bureau  Bui.  Q) 

(To  1906,  Degrees  Fahrenheit) 


October 

November 

18 

2 

22 

5 

19 

1 

23 

-10 

22 

14 

26 

15 

23 

15 

16 

9 

24 

14 

19 

15 

20 

2 

21 

6 

19 

-18 

12 

3 

7 

-20 

16 

-  6 

20 

-  2 

29 

23 

22 

14 

12 

-13 

13 

-22 

24 

-  9 

36 

27 

36 
40 

27 
34 

19 

10 

January 

February 

-24 

-24 

-14 

-16 

-12 

-12 

-24 

-18 

-11 

-13 

-  1 

-  9 

-  2 

-13 

-12 

-10 

-  1 

-  5 

-  8 

-22 

-20 

-22 

-17 

-29 

-20 

-13 

-  7 

-18 

-42 

-36 

-13 

-15 

-13 

-19 

10 

11 

-  6 

3 

-30 

-23 

-15 

-22 

-17 

-15 

19 

21 

20 

24 

30 

28 

-  4 

-14 

Lewiston,  Maine.  .  .  . 

Fitchburg,  Mass 

Rochester,  N.  Y 

Albany,  N.  Y 

Vineland,  N.  J 

Charlottesville,  Va. . 
Martinsburg,  W.  Va 
WajTiesville,  N.  C. . 

Clayton,  Ga 

Marietta,  Ohio 

Griggsville,  111 

Springfield,  Mo .... 
Montrose,  Colo .... 

Provo,  Utah 

Missoula,  Mont. . .  . 

Fayette,  Idaho 

The  Dalles,  Ore.... 

Albany,  Ore 

Roseburg,  Ore 

Spokane,  Wash 

Moxee  Wells,  Wash. 
Walla  Walla,  Wash. 
Sacramento,  Cal. .  . . 

Fresno,  Cal 

Los  Angeles,  Cal. . . . 
Roswell,  N.  M 


-21 
-14 
-11 
-17 

-  5 
4 

-  2 

-  4 
2 

-  4 
-16 
-11 
-17 

-  6 
-23 

-  6 
-18 

18 

7 

-18 

-  8 

-  2 
24 
23 
30 

-  3 


The  Effect  of  Bodies  of  Water  on  Temperature.— Large  bodies  of 
water  have  been  said  to  retard  temperature  changes,  making  conditions 
.in  their  vicinity  rather  more  favorable  for  fruit  growing.  Table  5 
assembles  data  showing  mean  monthly  temperatures  for  stations  selected 


THE  GEOGRAPHY  OF  FRUIT  GROWING 


629 


Table  5. — Monthly  Mean  Temperatures  at  Coastal  and  at  Inland  Points 

{Compiled  from  Bigelow^) 
(Degrees  Fahrenheit) 


1.  Grand  Haven,  Mich 

2.  Grand  Rapids,  Mich 

3.  Buffalo,  N.  Y 

4.  Syracuse,  N.  Y 

5.  Milwaukee,  Wis 

6.  Madison,  Wis 

7.  Eastport,  Maine 

8.  Northfield,  Vt 

9.  Erie,  Pa 

10.  Scranton,  Pa 25. 

11.  Charles  City,  Iowa 11. 

12.  Dubuque,  Iowa 18, 


'o/i    o  in  a 


■.\ 


^1 
533. 

031 

831 


8|44. 
046. 
2'42. 
4|44. 
941. 
1J44. 
938. 
2  40. 

44. 

47. 

46. 

48. 


8  64. 

0  68. 

5[65. 

66. 


7  69.7  67. 
1  72.  6l70. 


1,70.2 
9  70.8 

5  69.7 

3  72.4 

4  59.8 

7  66.6 
0J71.8 
2J71.8 

8  73.5 

6  74.7 


61.1 

61.8 
8|62.9 
661.6 
761.5 


61.1 
55.2 
54.6 
63.9 
62.2 


38.  o; 

38.1 

39.3; 

38.7 

36.1 

34.2; 

36.8; 

32.  o; 

41. 
39.1 
33.0  19.0 
36.0  24.5 


30.1 
28.8 
1 

28.3 
26.0 
22.7 
25.3 
20.5 
31.7 


to  illustrate  this  influence.  With  the  exception  of  the  Iowa  points,  the 
stations  are  arranged  in  contrasting  pairs,  the  odd-numbered  stations 
being  located  close  to  considerable  bodies  of  water.  In  practically  every 
case  these  stations  show  higher  January  means  and  lower  July  means 
than  the  respective  stations  with  which  they  are  contrasted.  In  every 
case  the  April  temperature  for  the  inland  station  is  higher  and  November 
temperature  lower  than  at  the  points  near  water.  The  Iowa  stations  of 
approximately  the  same  latitude  as  the  majority  of  the  more  eastern 
points  show  intensification  in  all  these  differences.  Milwaukee  and 
Grand  Haven,  at  almost  opposite  points  on  Lake  Michigan,  show  the 
influence  of  the  lake  on  the  prevailing  winds  blowing  over  it.  That  the 
retardation  for  these  stations  is  generally  somewhat  greater  in  the  spring 
than  in  the  fall  is  shown  by  Table  6. 


Table  6. — Dates  When  Normal  Temperature  Crosses  40°F. 
{Compiled  from  Bigelow'^) 

1.  Grand  Haven,  Mich Apr.     7  Nov.    8 

2.  Grand  Rapids,  Mich Apr.     3  Nov.    9 

3.  Buffalo,  N.  Y Apr.    11  Nov.  12 

4.  Syracuse,  N.  Y Apr.     7  Nov.  11 

5.  Milwaukee,  Wis Apr.    12  Nov.    5 

6.  Madison,  Wis Apr.     7  Nov.    2 

7.  Eastport,  Maine Apr.  23  Nov.    5 

8.  Northfield,  Vt Apr.   16  Oct.    25 

9.  Erie,  Pa Apr.     5  Nov.  17 

10.  Scranton,  Pa Mar.  30  Nov.  12 

11.  Charles  City,  Iowa Apr.     4  Nov.    2 

12.  Dubuque,  Iowa Mar.  31  Nov.    7 


630  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Attention  may  be  called  to  some  of  the  northern  finger-like  extensions 
of  the  Lower  Austral  zone  into  latitudes  that  for  the  most  part  belong  in 
the  Transition  zone.  Those  along  the  eastern  shore  of  Lakes  Michigan 
and  Huron,  the  southern  shores  of  Lakes  Erie  and  Ontario  and  the  eastern 
shore  of  Lake  Champlain  are  cases  in  point  and  illustrate  the  extent  to 
which  chmate  is  tempered  and  consequently  life  zones  are  modified 
through  the  influence  of  large  bodies  of  water.  Lippincott  gives  one 
concrete  illustration  of  this  influence  :*i  On  Jan.  1,  1864,  a  cold  wave 
swept  over  the  north  central  part  of  the  United  States.  Many  Minnesota 
points  registered  temperatures  as  low  as  —  38°F. ;  at  Milwaukee  the 
thermometer  went  to  —  30°F.;  yet  at  Holland,  Mich.,  across  Lake  Michi- 
gan from  Milwaukee —8°F.  was  the  lowest  temperature  recorded. 
Further  inland,  at  Lansing,  Mich.,  however,  —  22°F.  was  experienced. 
Peach  buds  were  uninjured  in  a  narrow  belt  along  the  eastern  shore  of  the 
lake  but  were  killed  at  distant  points.  The  data  for  Milwaukee  and 
Grand  Haven  in  Table  5  show  that  this  influence  is  constant. 

Influence  of  Altitude  on  Air  and  Soil  Temperatures. — It  is  well  known 
that  an  increase  in  altitude  is  accompanied  by  many  of  the  same  changes 
as  an  increase  in  latitude,  the  most  important  being  one  in  temperature. 
It  is  true  also  that  an  increase  in  altitude  is  accompanied  by  certain 
changes  in  physical  environment  that  are  not  found  at  correspondingly 
higher  latitudes.  Thus  Kerner  and  Oliver  report  that  in  the  Tyrolese 
Alps  at  an  altitude  of  2600  meters  the  chemical  activity  of  the  sun's  rays 
is  11  per  cent,  greater  than  at  sea  level.  This  alone  may  account  for 
some  of  the  peculiarities  of  plant  associations  noted  at  different  altitudes 
and  possibly  may  go  far  toward  explaining  the  more  brilliant  and  intense 
coloring  of  certain  fruits  and  their  better  finish  at  high  altitudes.  The 
same  authors  report  a  different  ratio  between  mean  soil  and  air  tempera- 
tures at  high  as  compared  with  low  elevations  (see  Table  7)  and  this  too 
may  either  intensify  or  suppress,  as  the  case  may  be,  the  differences 
associated  with  variations  in  air  temperature  only. 

Table  7. — Increase  of  Mean  Soil  Temperature  Over  Mean  Air  Temperature 
WITH  Increased  Altitude  in  Tyrolese  Alps^^ 


Excess  of  mean  soil  temperature  over 

Elevation,  meters 

mean  air  temperature,  degrees  Centigrade 

1000 

1.5 

1300 

1.7 

1600 

2.4 

1900 

3.0 

2200 

3.6 

THE  GEOGRAPHY  OF  FRUIT  GROWING  631 

GEOGRAPHY  OF  FRUIT  PRODUCTION  AS  INFLUENCED  BY  RAINFALL  AND 

HUMIDITY 

Of  hardly  less  significance  than  temperature  is  the  influence  of  humid- 
ity in  determining  the  limits  of  life  and  crop  zones  and  in  the  geography 
of  fruit  growing.  By  humidity  is  meant  here  total  rainfall,  distribution 
throughout  the  season,  availability  for  plant  growth  and  atmospheric 
humidity.  Only  in  countries  or  districts  where  the  topography  leads  to 
marked  differences  in  rainfall  between  points  close  together  and  enjoying 
practically  the  same  temperatures  are  the  full  effectsof  humidity  strikingly 
brought  out.  Thus  "  .  .  .at  one  of  the  substations  of  the  United  States 
Experiment  Station  on  the  Island  of  Hawaii,  a  rainfall  of  360  inches  was 
recorded  for  1  year,  while  at  a  point  28  miles  away  the  annual  rainfall  for 
the  same  year  was  6  inches.  It  is  possible  ...  in  the  space  of  an  hour's 
ride  to  pass  from  a  desert  covered  with  cacti  and  other  drought-resistant 
plants  into  a  dense  tropical  jungle  reeking  with  moisture." ^^ 

For  the  most  part  fruit  trees  thrive  better  in  a  fairly  humid  climate, 
a  fact  shown  by  the  natural  distribution  of  their  undomesticated  relatives. 
Many  species,  however,  like  the  date  palm  and  olive,  succeed  in  a  very 
arid  climate.  Some  of  the  great  variations  in  the  actual  water  require- 
ments of  different  kinds  of  fruit  are  shown  by  data  presented  in  the  sec- 
tion on  Water  Relations.  Often  different  varieties  of  the  same  kind 
of  fruit  vary  considerably  in  water  requirements.  The  Yellow  Trans- 
parent apple  will  thrive  and  produce  good  fruit  on  less  water  than  the 
Winesap  or  York.  Certain  varieties  or  types  of  dates  are  grown  at 
Alexandria,  Egypt,  where  the  mean  atmospheric  humidity  is  from  64  to 
72  per  cent,  while  certain  other  varieties  are  grown  in  some  of  the  desert 
oases  having  an  atmospheric  humidity  of  only  34  per  cent.  Those  varie- 
ties that  thrive  under  the  one  set  of  conditions,  however,  cannot  be  grown 
successfully  in  the  other  environment.^^  As  these  humidity  requirements 
of  different  fruits  become  known  it  is  possible  to  draw,  more  or  less  accur- 
ately, iso-hyetal  lines  setting  approximate  boundaries  for  districts  in 
which  they  may  be  expected  to  reach  a  high  degree  of  development. 

Data  presented  in  Table  8,  however,  show  the  danger  in  placing  too 
much  reliance  upon  rainfall  figures  as  an  index  to  fruit  crop  or  varietal 
adaptation.  Thus  Fitchburg,  Mass.  has  a  mean  annual  rainfall  of  45.4 
inches,  28.6  coming  during  the  growing  months,  while  Missoula,  Mont., 
has  a  total  precipitation  of  only  15.5  inches,  of  which  10.4  comes  during 
the  growing  months;  yet  both  are  apple  growing  centers  and  Mcintosh 
is  one  of  the  most  satisfactorj^  varieties  in  both  places.  Irrigation,  how- 
ever, is  employed  in  Montana.  Vineland,  N.  J.,  has  an  annual  rainfall 
of  47.3  inches,  three-fourths  of  which  falls  during  the  growing  season; 
yet  The  Dalles,  Ore.,  with  less  than  one-third  of  that  total  rainfall  and 
with  only  one-sixth  as  much  falling  during  the  growing  season  as  comes 
during  the  corresponding  period  in  New  Jersey,  produces  peaches  and 


632 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


other  stone  fruits  with  success  and  without  the  aid  of  irrigation.  A 
season  with  a  summer  rainfall  as  low  as  that  of  The  Dalles,  would  involve 
considerable  loss  in  New  Jersey.  The  summer  temperatures  of  the  two 
locations  are  very  much  alike,  as  shown  in  Table  3.  Irrigation  is  con- 
sidered an  absolute  necessity  in  many  localities  with  higher  yearly  and 
growing  season  rainfalls  than  those  of  The  Dalles.  The  explanation  of  the 
ability  of  the  Oregon  section  to  produce  fruit  successfully  and  with  such 
a  limited  water  supply  lies  in  the  depth  and  character  of  its  soil  and  in  the 
methods  of  soil  management  employed.  The  data  in  this  table,  however, 
taken  in  consideration  with  the  methods  of  culture  that  are  practiced  and 
the  varieties  that  are  grown  in  the  different  sections  point  out  certain 
general  limitations  that  are  placed  on  fruit  culture  by  rainfall  and  the 
methods  that  may  be  employed  by  fitting  practice  and  variety  to  varying 
conditions  of  humidity. 


Table  8. — Mean  Rainfall  of  Selected  Stations 

(Compiled  Chiefly  from  United  States  Weather  Bureau  Bui.  Q) 

(inches) 


Rumford  Falls,  Mail 

Fitchbiirg,  Mass 

Rochester,  N.  Y 

Albany,  N.  Y 

Vineland,  N.  J 

Martinsburg,  W.  Va 
Charlottesville,  Va. . 
Waynesville,  N.  C. . 

Clayton,  Ga 

Marietta,  O 

Griggsville,  111 

Springfield,  Mo 

Montrose,  Colo 

Provo,  Utah 

Missoula,  Mont 

Payette,  Idaho 

The  Dalles,  Ore 

Albany,  Ore 

Roseburg,  Ore 

Spokane,  Wash 

Moxee  Wells,  Wash. 
Walla  Walla,  Wash. 
Sacramento,  Cal. .  .. 

Fresno,  Cal 

Los  Angeles,  Cal. . .  . 

Roswell,  N.  M 

Sitka,  Alaska 

Lincoln,  Neb 


3.0 
3.3 
2.4 
2.4 


1.0 
1.  1 
1.0 
1.0 
0.7 
3.6 
2.5 
1.3 
0.6 
1.8 
2.0 
0.6 
1.  1 
0.4 
6.3 
2.8 


3.7 
3.6 
3.0 
3.0 
3.7 
4.2 
5.  1 
3.7 
3.2 
4.0 
5.3 
5.9 
0.7 
1.5 
2.2 
1.4 
0.6 
2.6 
2.0 
1.4 
0.9 
1.7 
1.0 
0.5 
0.5 
1.2 
3.5 
4.3 


3.8 
3.0 
3.1 
3.7 
3.6 
3.6 
5.5 
4.4 
5.3 
4.5 
4.5 
4.8 
0.2 
0.5 
2.1 
0.6 
0.6 


4.5 
2.9 
3.1 
3.9 
4.6 
3.7 
5.7 
4.6 
7.0 
4.4 
3.7 
4.2 
0.8 
0.2 
1.0 
0.4 
0.  1 
0.3 
0.4 
0.7 
0.  1 
0.4 
T 
T 
T 
3.4 
4.2 
3.8 


3.2 
4.4 
2.9 
4.0 
4.8 
3.2 
5.0 
4.5 
7.2 
3.9 
2.7 
3.9 
1.  2 
0.2 
0.7 
0.3 
0.2 
0.4 
0.4 
0.5 
0.2 
0.4 
T 
T 
T 
2.2 
6.7 
3.7 


3.0 
3.4 
2.3 
3.2 
3.8 
2.5 
5.2 
2.4 
4.9 
3.0 
4.0 
3.8 


0.4 
1.2 
0.5 
0.6 
2.0 
1.  1 
1.0 
0.4 
1.0 
0.3 
0.3 
0.8 
2.0 
10.7 
2.6 


3.0 
4.0 
2.8 
3.  1 
3.6 
1.6 
3.5 
2.1 
4.0 
2.9 
1.9 
2.9 
0.8 
0.8 
1.2 
1.0 
1.3 
3.4 
2.6 
1.4 
0.5 
1.5 
1.1 
0.6 
1.5 
1.6 
12.1 
1.8 


28.3 

28.6 

22.7 

26.  1 

31.7 

25.1 

37.0 

32.2 

45.7 

29.2 

28.6 

33.2 

6.5 

6.0 

10.4 

6.  1 

5.4 


7.4 
3.6 
6.7 
13.0 
52.1 
24.6 


42.1 
45.4 
34.5 
36.9 
47.3 
35.2 
49.8 
47.7 
68.5 
42.1 
37.0 
43.6 

9.3 
10.9 
15.5 
12.1 
15.4 
44.2 
34.9 
18.3 

8.9 
17.7 
19.9 

9.2 
15.6 
15.6 
82.3 
27.5 


THE  GEOGRAPHY  OF  FRUIT  GROWING 


633 


OTHER  FACTORS  INFLUENCING   THE   GEOGRAPHIC  DISTRIBUTION   OF 

FRUITS 

Sunshine. — The  amount  of  sunshine  to  which  the  trees  are  exposed 
during  their  growing  season  is  perhaps  of  secondary  importance  in  deter- 
mining the  character  of  the  fruit  industry  that  may  develop  in  different 
sections,  since  it  nowhere  becomes  so  reduced  as  to  be  permanently  a  Hmit- 
ing  factor.  However  it  is  often  decisive  in  determining  the  varieties  that 
can  be  grown  to  advantage.  This  is  true  at  least  in  the  apple  in  which 
coloration  depends  directly  on  the  relative  amount  of  sunshine  that  reaches 
the  fruit  during  the  ripening  season.  Thus  the  data  in  Table  9  suggest 
why  it  is  practicable  to  grow  varieties  like  Winesap  at  Grand  Junction, 
Col.  and  in  eastern  Washington,  but  not  in  the  vicinity  of  Portland, 
Ore. 


Table  9.— Hours  of  Sunshine  for  Selected  Stations 
(Compiled  from  United  States  Weather  Bureau  Bui.  Q) 

March 

April 

May 

June 

July 

August 

September 

October 

19.5 
186 
171 
152 
198 
197 
178 
199 
192 
128 
196 
193 
252 
194 
166 
241 
255 

213 
240 
225 
221 
250 
255 
236 
240 
204 
181 
222 
236 
279 
235 
200 
324 
275 

258 
279 
266 
263 
284 
312 
244 
267 
232 
224 
294 
288 
337 
286 
230 
370 
259 

274 
300 
290 
287 
293 
303 
275 
295 
261 
240 
354 
355 
369 
330 
329 
404 
289 

276 
279 
296 
318 
299 
274 
312 
341 
291 
279 
405 
370 
370 
372 
268 
429 
341 

258 
248 
258 
269 
271 
253 
256 
290 
279 
240 
354 
329 
317 
310 
183 
400 
328 

232 
240 
223 
213 
271 
250 
235 
250 
252 
199 
298 
296 
312 
226 
148 
336 
282 

185 

Albany,  N.  Y 

Rochester,  N.  Y 

Erie,  Pa 

Raleigh,  N.  C 

Atlanta    Ga 

186 
158 
157 
220 
235 

St   Paul    Minn 

176 

202 

Kansas  City,  Mo 

Parkersburg,  W.  Va..  .  . 
Boise,  Idaho 

236 
159 
216 

Salt  Lake  City,  Utah... 
Grand  Junction,  Col.... 
Spokane    Wash 

236 
265 
160 

Portland,  Ore 

Fresno,  Cal 

Los  Angeles,  Cal 

64 
290 

263 

Parasites. — The  prevalence  of  certain  parasites  is  another  factor  of  no 
mean  importance  in  determining  the  geographic  distribution  of  fruit 
growing — at  least  in  determining  what  kinds  of  fruit  shall  be  grown 
in  different  districts.  For  instance,  European  grapes  are  not  grown  in 
the  southeastern  United  States  on  account  of  the  prevalence  there  of  the 
grapevine  phylloxera  and  the  downy  mildew.  European  plums  are 
commercially  unimportant  in  the  Middle  West  on  account  of  the  brown 
rot  and  the  black  knot.  Perhaps  in  the  last  analysis  certain  insects  and 
diseases  are  particularly  troublesome  in  certain  districts  because  they 
find  there  temperature  and  humidity  conditions  that  are  especially  favor- 
able for  their  development  and  spread ;  hence  fundamentally  it  is  temper- 
ature or  humidity  that  really  sets  limits  for  these  fruits.     Nevertheless 


634  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

the  immediate  factor  responsible  for  limitation  of  the  industry  is  a 
parasite. 

Wind.— Wind  is  often  considered  important  in  determining  whether 
fruits  can  or  cannot  be  grown  successfully  in  certain  sections.  It  is  to 
be  doubted  if  wind  alone  is  of  great  significance  over  any  wide  areas.  On 
the  other  hand,  extreme  heat  or  dryness  accompanied  by  winds  may 
cause  much  damage  and  practically  prevent  the  culture  of  certain  fruits 
in  large  areas  where  they  frequently  occur.  Actually  in  such  cases  it  is 
the  combination  of  high  temperature  or  low  humidity — or  both — with  the 
wind  that  is  the  real  factor. 

Native  Range  of  Parent  Species. — The  native  range  of  the  parent 
species  without  doubt  furnishes  some  indication  of  the  probable  geo- 
graphic range  of  the  forms  that  are  brought  under  cultivation;  neverthe- 
less it  is  doubtful  if  it  is  an  index  with  most  fruits  of  the  extent  to  which 
they  may  be  grown  for  commercial  production.  For  instance,  the  com- 
mon European  plum  {Prunus  domestica)  is  native  to  central  and  south- 
eastern Europe.  Its  cultivation  extends  to  practically  all  of  Europe 
and  to  much  of  temperate  North  America  and  it  is  grown  to  a  limited 
extent  in  many  other  parts  of  the  world.  Though  the  native  home 
of  the  peach  is  supposed  to  be  China,  it  reaches  its  greatest  commercial 
importance  in  Europe,  North  America  and  southern  Africa.  The 
Evergreen  blackberry  (Ruhus  laciniatus)  apparently  is  not  cultivated  in 
southwestern  Europe  where  it  is  found  wild,  but  is  of  considerable  impor- 
tance in  the  Pacific  Northwest  6,000  miles  from  its  native  home.  On 
the  other  hand  the  culture  of  the  North  American  phim  {Prunus  ameri- 
cana)  is  restricted  to  an  area  considerably  less  than  the  native  range  of 
the  parent  species  and  the  litchi  (Nephelhmi  litchi)  is  not  grown  com- 
mercially outside  China. 

Length  of  Time  in  Cultivation. — The  length  of  time  a  species  has  been 
under  cultivation  naturally  has  some  influence  on  the  amount  of  territory 
over  which  it  extents.  Fruits  of  recent  introduction,  such  as  the  pecan, 
the  blueberry  and  the  loganberry  have  not  had  time  to  become  dissemin- 
ated widely  and  tried  thoroughly  in  many  sections.  On  the  other  hand, 
though  the  Chinese  jujube  probably  has  been  in  cultivation  as  long  as 
the  peach,  its  present  geographic  range  is  very  small  as  compared  with 
that  of  its  sister  fruit  coming  from  the  same  general  region.  Some 
species,  such  as  the  fox  grape  ( Vitis  labrusca) ,  are  cultivated  over  a  very 
wide  range  of  territory  though  they  have  been  in  cultivation  only  a  few 
decades. 

Uses  and  Quality  of  Product. — The  variety  of  uses  that  the  fruit  and 
the  plant  producing  it  serves  has  been  doubtless  an  important  factor  in 
making  the  cocoanut  palm  one  of  the  most  widely  distributed  fruits  in 
cultivation.  For  many  tropical  peoples  it  is  the  one  most  important 
plant  and  there  has  thus  been  every  encouragement  to  disseminate  it 


THE  GEOGRAPHY  OF  FRUIT  GROWING  635 

widely.  The  same  may  be  said  of  the  banana.  On  the  other  hand, 
though  the  date  pahii  and  the  fig  are  hardly  less  important,  their  actual 
cultural  range  is  much  more  restricted. 

Quality  of  product  is  certainly  relatively  unimportant  in  determining 
geographic  distribution.  Best  evidence  on  this  point  is  obtained  by  a 
comparison  of  varieties  within  a  group,  for  it  is  hardly  fair  to  compare  the 
quality  of  one  group,  for  example  the  orange,  with  that  of  another,  for 
example  the  raspberry.  Though  Elberta  is  admittedly  a  second  rate 
peach  in  quality,  it  dominates  the  peach  industry  of  America.  The 
Kieffer  pear  and  the  Ben  Davis  apple  occupy  similar,  though  perhaps  not 
quite  so  prominent,  positions  in  their  respective  groups. 

Relation  to  Consuming  Centers  and  Transportation  Facilities. — The 
location  of  large  consuming  centers  and  their  relation  to  efficient  systems 
of  transportation  is  very  important  in  determining  where  many  fruits, 
particularly  those  of  a  more  perishable  character,  are  grown  in  quantity. 
For  instance  a  map  showing  the  distribution  of  the  strawberry  industry 
of  North  America  indicates  production  centers  close  to  nearly  all  the 
larger  markets;  those  production  centers  distantly  located  from  large 
markets  are  connected  with  them  by  good  transportation  systems. 
The  same  statements  hold  for  raspberry,  blackberry  and  dewberry  pro- 
duction and  to  a  certain  extent  for  fruits  like  the  peach,  cherry  and  plum. 
However,  many  centers  of  heavy  production  of  these  fruits  are  not  par- 
ticularly well  located  from  the  standpoint  of  nearby  markets  or  quick 
and  cheap  transportation.  Almost  invariably  the  presence  of  fruit 
product  plants  of  one  kind  or  another  makes  possible  the  location  of  the 
industry.  Were  it  not  that  a  comparatively  large  percentage  of  the 
world's  grape  crop  has  been  utilized  for  wine  making  for  thousands  of 
years,  it  might  be  said  that  fruit  product  facilities  are  becoming  of 
increasing  importance  in  determining  the  location  of  fruit  production 
centers. 

Sometimes  factors  that  are  more  or  less  artificial  operate,  at  least  for  a 
time,  in  determining  the  development  of  large  fruit  industries.  For  in- 
stance a  large  fruit  product  establishment  may  be  located  at  some  point — 
its  exact  location  being  determined  largely  by  considerations  quite  dis- 
tinct from  those  concerned  with  fruit  production.  Within  a  short  time 
a  large  fruit  industry  develops  in  the  vicinity  of  this  plant  to  supply  it 
with  fresh  fruit.  Had  this  plant  been  located  a  hundred  miles  away,  the 
first  place  would  have  raised  no  fruit  commercially  but  the  industry  would 
have  developed  around  the  other.  It  often  happens  that  a  pioneer 
in  some  branch  of  horticulture  makes  a  marked  success  of  growing  some 
particular  kind  of  fruit.  His  neighbors  promptly  follow  him  in  the  busi- 
ness and  soon  a  whole  community  or  a  whole  section  becomes  famous  for 
its  Cuthbert  raspberries,  or  Mcintosh  apples,  or  Evergreen  blackberries 
or  Neunan  strawberries.     In  the  long  run,  however,  a  specialized  indus- 


636  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

try  develops  and  remains  chiefly  in  those  sections  or  districts  where  fac- 
tors governing  production,  harvesting,  distribution  and  marketing  are 
most  favorable.  In  other  words,  the  present  geographic  distribution  of 
the  different  fruit  industries  represents  the  result  of  a  struggle  for 
existence,  a  real  natural  selection. 

Summary.^ — The  most  important  environmental  factor  determining 
the  geographic  range  of  cultivated  fruits  is  temperature,  though  rainfall 
and  humidity  act  as  important  limiting  factors  within  the  wider  limits  set 
by  temperature.  The  boundary  lines  of  fruit  zones  follow  rather  closely 
those  of  the  life  zones  established  by  the  biologist.  Apparently,  mini- 
mum winter  temperatures  are  most  important  in  setting  the  northern 
limits  (in  the  Northern  Hemisphere)  to  the  geographic  range  of  species 
and  varieties  and  mean  summer  temperature  during  the  hottest  6  weeks 
in  setting  their  southern  bounds.  The  limiting  effects  of  natural  rainfall 
are  often  alleviated  by  the  use  of  irrigation  water  or  by  other  cultural 
practices  and  also  by  the  selection  of  drought  resistant  varieties.  Sun- 
shine, wind  and  the  presence  of  certain  parasites  are  often  important 
factors  in  determining  the  range  of  particular  varieties.  There  is  no 
very  close  relation  between  the  length  of  time  a  species  or  variety  has  been 
in  cultivation  or  between  the  natural  range  of  related  forms  and  its 
range  in  cultivation.  Artificial  factors,  such  as  nearness  to  large  centers 
of  population,  transportation  and  storage  facilities,  and  temporary 
market  demands,  often  are  of  considerable  importance  in  determining  the 
approximate  range  of  a  variety  or  of  a  fruit  and  in  determining  its 
elative  importance  within  different  portions  of  its  range. 


CHAPTER  XXXIV 
ORCHARD  LOCATIONS  AND  SITES 

The  production  of  fruit  on  a  scale  sufficient  to  meet  the  needs  of  the 
home  at  least  partly  has  a  general  appeal.  Indeed  it  is  exceptional  to  find 
the  farm  or  even  the  suburban  lot  that  is  without  trace  of  fruit  tree, 
shrub  or  vine.  Such  planting  of  a  few  fruit-producing  plants  is  often  done 
as  much  for  the  pleasure  derived  from  their  culture  as  for  the  monetary 
returns.  On  the  other  hand,  commercial  fruit  production  is  a  business 
and  appeals  to  only  a  comparatively  small  percentage  of  the  popula- 
tion— even  of  the  farming  population.  Perhaps  this  is  because  it  is 
generally  considered  an  exacting  business,  requiring  special  training  or 
special  aptitude,  or  perhaps  it  is  due  to  other  reasons.  Whatever  the 
reason,  the  commercial  fruit  growers  are  few  in  comparison  with  other 
classes  of  farmers.  Nevertheless  there  are  frequent  recurring  waves  of 
interest  in  commercial  fruit  production,  bringing  to  those  already  engaged 
in  some  line  of  farming  the  question  whether  or  not  it  would  be  desirable 
for  them  to  set  a  part  of  their  acreage  to  fruit,  or  raising  in  the  minds 
of  those  who  are  not  engaged  in  agriculture  the  question  whether  they 
might  not  raise  fruit  with  profit.  In  either  case  a  number  of  matters 
concerning  the  establishment  of  an  orchard  should  be  considered  before 
any  definite  decision  is  made.  These  questions  are  much  the  same 
fundamentally  for  the  one  group  of  prospective  growers  as  for  the  other, 
though  the  points  of  view  may  be  somewhat  different.  In  the  one  case 
the  problem  is  to  determine  what  fruits  can  be  grown  to  best  advantage 
in  some  particular  field,  farm  or  locality;  in  the  other  it  may  take  the 
form  of  first  deciding  on  what  kinds  to  grow  and  then  in  finding  the  proper 
place  to  grow  them. 

Orcharding  In  or  Outside  of  an  Established  Fruit  Growing  Section. — 
Incidental  to  the  discussion  of  the  geography  of  fruit  growing  some  of  the 
factors  influencing  the  choice  of  a  location  for  certain  fruits  or  of  fruits 
for  certain  locations  are  mentioned.  An  intelligent  selection  in  either 
case  depends  on  a  detailed  knowledge  of  the  geographic  distribution  of  the 
industries  concerned.  Obviously  there  would  be  considerable  risk  in  the 
commercial  culture  of  some  fruit  in  a  section  where  it  is  not  being  grown — 
where  it  has  never  been  tried  or  where  its  cultivation  has  been  discon- 
tinued. Thus  it  would  not  seem  wise  to  attempt  commercial  filbert 
culture  in  New  York  or  Pennsylvania,  or  to  make  other  than  experimental 
plantings  of  the  jaboticaba  in  southern  Florida.     It  would  be  safer 

637 


638  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

to  undertake  the  commercial  production  of  any  fruit  where  an  industry  in 
that  particular  fruit  is  already  established. 

One  great  advantage  in  producing  fruit  of  a  kind  that  is  well  and 
favorably  known  and  in  a  section  where  it  is  extensively  grown  is  that 
the  marketing  problem  usually  presents  fewer  difficulties.  The  reputa- 
tion attracts  buyers  and  the  fact  that  growers  have  been  established  there 
often  means  that  efficient  selling  organizations  have  been  formed.  How- 
ever, such  marketing  advantages  are  often  over-emphasized.  In  years 
of  heavy  production,  the  apple  grower  in  western  New  York  may  wish 
his  orchard  were  in  Indiana  or  Nebraska.  Moreover,  land  prices  are 
likely  to  be  high  in  sections  with  established  reputations;  this  means  a 
permanently  large  overhead  charge  in  the  cost  of  production.  If  fruit 
is  to  be  grown  under  these  conditions,  the  choice  of  kinds  and  varieties 
and  the  methods  of  culture  must  be  such  as  will  yield  large  returns. 
The  usual  advantages  of  production  where  little  fruit  is  raised  are  cheap 
land  and  good  local  markets.  However,  isolation  may  mean  difficulty 
in  getting  in  contact  with  buyers,  trouble  in  securing  supplies  and  no 
possibility  of  cooperative  effort.  Probably  much  would  depend  on 
the  scale  of  operations  contemplated.  The  small  grower  can  often 
produce  to  better  advantage  in  the  less  developed  sections,  though 
conditions  favorable  to  developing  a  large  enterprise  are  more  likely 
to  be  found  where  an  industry  of  some  size  is  already  established. 

Land  Values. — Among  the  important  factors  determining  the  desir- 
ability of  a  piece  of  land  for  fruit  growing  are :  land  values,  the  availability 
of  transportation  and  storage  facilities,  of  fruit  products  establishments, 
of  labor  supply,  the  social  conditions  and  the  educational  advantages. 
Locations  only  a  few  miles  apart  may  vary  greatly  in  respect  to  one  or  all 
of  these  factors. 

Perhaps  the  price  paid  for  land  or  its  valuation  has  nothing  to  do 
with  the  grade  or  quantity  of  fruit  that  can  be  produced  on  a  given  area 
and  the  question  of  conditions  favorable  for  production  can  possibly  be 
considered  entirely  aside  from  it.  Nevertheless  it  should  be  realized 
that  successful  orcharding  is  a  question  not  only  of  production,  but 
even  more  of  economical  production.  This  means  that  there  must  be  a 
reasonably  large  margin  between  production  costs  and  selling  prices. 
Both  production  costs  and  selling  prices  for  fruit  fluctuate  from  year  to 
year  and  the  difference  between  them  will  likewise  vary,  but  interest  on 
investment  constitutes  a  fixed  and  important  part  of  the  overhead  charges 
figured  into  the  cost  of  production.  This  charge  must  be  discounted 
every  year,  crop  or  no  crop.  For  instance,  if  the  orchard  at  bearing  age 
represents  an  investment  of  $300  per  acre  and  it  yields  an  average  crop 
of  300  bushels  per  acre  the  interest  charge  against  each  bushel  is  about 
6  cents;  if,  however,  the  orchard  represents  an  investment  of  $1,000  per 
acre,  a  crop  of  the  same  size  would  represent  an  interest  charge  of  20 


ORCHARD  LOCATIONS  AND  SITES  639 

cents  per  bushel.  Of  course,  if  a  bumper  crop  were  harvested  in  the 
latter  case — a  crop  say  of  600  bushels  per  acre — the  interest  charge  per 
bushel  would  be  only  10  cents;  but  on  the  other  hand  if  a  light  crop,  say 
100  bushels,  is  harvested,  the  interest  charge  per  bushel  would  be  60 
cents.  It  is  not  the  intent  here  to  recommend  cheap  land  for  growing 
fruit;  such  land  may  prove  the  most  expensive  in  the  end.  On  the  other 
hand  the  purchaser  or  owner  of  high  priced  land  should  figure  out  before 
planting  the  probable  charges  per  bushel,  pound,  barrel  or  other  unit  of 
fruit  produced,  that  the  cost  of  land  contributes  toward  cost  of 
production. 

Transportation  Facilities. — The  importance  of  the  distance  between 
the  orchard  and  the  shipping  point  or  the  market  depends  on  the  character 
of  the  roads  and  the  value  and  nature  of  the  crop.  Of  course  the  ideal 
location  is  adjacent  to  a  railroad  or  other  transportation  system  so  that 
there  may  be  facilities  for  loading  at  the  orchard.  Since  this  is  seldom 
possible,  access  to  a  loading  point  must  be  considered.  Six  or  eight 
miles  of  ordinary  country  road  has  been  considered  about  the  longest 
haul  practicable  with  most  fruits.  If  the  distance  to  the  shipping  point 
is  much  greater,  the  item  of  hauling  becomes  too  large  a  part  of  the  total 
cost  of  production  and  unduly  reduces  the  margin  of  profit,  or  possibly 
turns  profit  into  loss.  The  cost  per  mile  of  hauling  barreled  apples  over 
average  country  roads  should  not  exceed  2  to  3  per  cent  of  the  average 
price  received  for  them.  Let  the  distance  be  such  that  10  to  15  per  cent 
of  the  selling  price  is  required  to  cover  this  item  and  it  becomes  very 
important.  The  character  of  the  fruit  also  must  be  considered.  Obvi- 
ously it  is  impracticable  to  haul  strawberries  or  other  soft  fruits  as  far 
or  over  as  difficult  roads  as  winter  apples  may  be.  The  better  the 
road,  however,  the  greater  the  distance  the  crop  may  be  hauled  with- 
out injury.  A  trip  of  12  to  15  miles  over  well  graded  and  smooth  sur- 
faced roads  may  cause  much  less  injury  than  one  or  two  miles  over 
a  poor  country  road.  Finally  the  value  of  the  crop  per  load  is  important. 
Thus  it  may  be  entirelj^  practicable  to  plant  an  English  walnut,  prune 
or  chestnut  orchard  10  to  15  miles  from  a  shipping  point,  for  one  load 
would  carry  the  crop  from  2  acres,  while  a  corresponding  area  of  apple 
orchard  would  require  10  to  20  two-horse  load  trips.  Furthermore  a 
nut  crop  is  not  subject  to  the  mechanical  injury  which  would  result 
from  hauling  apples  long  distances. 

SLOPE  OR  ASPECT 

Many  advantages  have  been  claimed  for  certain  slopes — advantages 
so  great  that  prospective  fruit  growers  are  sometimes  led  to  believe  that 
success  is  practically  guaranteed  if  the  land  but  slopes  in  a  certain  direc- 
tion and  that  failure  is  almost  equally  certain  if  it  slopes  the  opposite 


640  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

way.  Southern  are  generally  warmer  and  earlier  than  northern  slopes 
because  they  receive  the  more  direct  rays  of  the  sun.  Shreve,^^  who 
has  studied  the  effect  of  varying  physical  environment  on  vegetation 
in  mountain  regions,  summarizes  some  of  the  more  important  influences 
as  follows:  "Two  slopes  of  the  same  inclination,  which  lie  in  opposed 
positions  so  that  one  faces  north  and  the  other  south,  will  present  to 
plants  two  environments  differing  in  almost  every  essential  physical 
feature.  The  temperature  of  the  air  on  two  such  slopes  might  be  identical 
as  determined  by  the  thermometer  of  a  carefully  established  meteoro- 
logical station,  but  they  are  distinctly  different  as  they  affect  vegetation, 
for  the  plants  receive  very  different  amounts  of  heat  through  diurnal 
terrestrial  radiation.  This  circumstance  is  of  small  importance  to  full- 
grown  trees  and  large  plants,  but  is  of  great  importance  to  young  plants 
and  seedlings.  The  soil  temperatures  of  opposed  slopes  are  also  widely 
unlike,  even  in  the  presence  of  the  undisturbed  cover  of  natural  vegeta- 
tion. The  two  opposed  slopes  would  in  all  likelihood  receive  the  same 
rainfall,  although  this  is  not  necessarily  the  case.  An  equal  amount  of 
rain  might  effect  an  equal  elevation  of  the  soil  moisture  on  the  two  slopes, 
and  to  the  same  depth,  but  the  soil  evaporation  of  the  south  slope  would 
greatly  exceed  that  of  the  north  slope,  and  a  lower  moisture  would  soon 
prevail  in  the  soil  of  the  former.  Greater  or  less  differences  may  thus 
be  shown  to  obtain  between  the  opposed  slopes  with  respect  to  the  most 
vital  features  of  plant  environment. " 

Influence  on  Soil  Temperatures  and  on  the  Plant. — Table  10  affords  a 
quantitative  expression  of  the  influence  of  slope  on  mean  soil  tempera- 
ture. Even  more  significant  are  the  differences  in  the  temperatures  of 
the  plants  themselves  on  different  slopes.  Table  11  shows  the  mean 
temperatures  one  inch  beneath  the  surface  of  the  bark  on  the  north  and 
south  sides  of  tree  trunks  at  the  summit  of  a  hill  and  on  its  north  and 
south  slopes  during  the  winter  months  in  Wisconsin.     As  would  be 

Table  10. — Mean  Soil  Temperatures  (Centigrade)  at  a  Depth  op  80  Centi- 
meters FOR  3  Years  on  Different  Slopes  of  an  Isolated  Conical 
Sandhill  at  Innsbruck,  Tyrol 
{After  Kerner  and  Oliver^'') 
N.  N.E.  E.  S.  E.  S.  S.W.  W.  N.W. 

15.3°  17.0°  18.7°         20.0°         19.3°         18.3°  18.5°  15.0° 

expected,  the  trees  on  the  south  slope  show  higher  midday  and  afternoon 
temperatures  than  those  on  the  northern  slope.  They  also  show  rather 
surprisingly  lower  early  morning  temperatures.  This  means  that  they 
are  exposed  to  greater  extremes  and  more  rapid  temperature  changes. 
The  relation  of  such  conditions  to  certain  forms  of  winter  injury  is  pointed 
out  in  .  the  section  on  Temperature  Relations.  The  tendency  of  the 
north  side  of  the  trunk  on  the  north  slope  to  be  colder  than  the  south  side 
in  the  early  morning  while  on  the  south  slope  the  reverse  condition  holds 


ORCHARD  LOCATIONS  AND  SITES 


641 


E 

a>  o  i^  05 

1 

d 

o  «  in  ro 

i-o 

£ 

<N  >ra  d  05 

IS 

'"' 

n  -H  r-.  CO 

IN 

S"o 

Is      <D 

:2 

e 

(N   t-    M   05 

00 

n 

-t"  -H  t^  r» 

c^ 

0) 

a 

00   00   00   h-" 

00 

_o 

c^              e^ 

"m 

E 

IN  ^  t-  ■* 

o> 

d 

t-   ^  N   o 

Oi 

to   M   00   -i 

X  i 

'" 

M   IN   (N    ■* 

CO 

I'S 

M     « 

■B 

i 

00  m  M  lo 

(^ 

to 

OS 

t^  o>  o  o 

•!«> 

00    t>^    oi    N^ 

00 

^ 

<N                 (N 

e 

t^    (N   t^    M 

o 

lo  -H  •*  00 

o 

» 

c. 

m'   to   t>;   OS 

tc' 

j3  is 

rl 

CO   -•    -<    N 

cs 

So 

^  £ 

S 

B 

00   t-   00   ■* 

f. 

" 

■a 

CO  CO  o  ■<< 

00   00   oi   00 

«■ 

t^ 

S                 (M 

's 

a 

r?. 

cc 

s 

05    O    00    N 

00 

S 

d 

Ji  to  in  ^_ 

CD 

_  £: 

m  IN  CO  ■* 

CO 

■C    «2 

o    ° 

•X     o 

!2 

E 

in  lo  IN  00 

-t< 

'S 

c3 

(N    CO   05    =D 

lO 

O!   00    00   N^ 

00 

'^ 

Ol                   <N 

o 

E 

to  05  m  00 

t-  in  in  IN 

00 

d 

Z 

M  00  d  in 

to" 

u 

CO    -H    IN    CO 

c^ 

S^ 

^1 

E 

O  CO  r^  CO 

^ 

(D   O   CO    -1 

s 

a 

00    C5    00    00 

t- 

C\                  (N 

■^ 

1 

E 

00  00  in  -1 

CO 

72 

d 

05    (N    -H    05 

00 

g 

IN    rt'   h-'   N.' 

C5 

h 

■*  CO  CO  ^ 

CO 

1? 

<2^ 

E 

C5    h-    CO    00 

05 

"53 

d 

05  m  t^  o 

o 

N.'  r-.  00  t-- 

t>l 

t^ 

C^                 (N 

^ 

u     :     '■     '. 

a     .    >,     . 

J    >.  ?     . 

Decern 
Januar 
Februa 
March 

c 

s 

§ 

1 

e 

k 

1 

1  £ 

o  in  o  o 

o  o  o  o 

e5 

to  to  to  to 

S 

H 

s 

e 

S  5 

in  o  o  o 

o  o  o  o 

-H     N     T)<     CO 

>-■  00  CO  in 

s 

H 

^ 

in  -c  CO  in 

05    CO    t~    05 

E 
a 

IN    -<    ■<l<    to 

o  05  in  T)- 

t-  to  00  CO 

K 

in  to  IN  to 

O    OS    OS    O 

E  2 

H 

>> 

in  to  t^  N 

in  05  w  ■* 

E 

£g§§ 

CO  in  to  t^ 

00    t^    X    00 

E 
d 

K 

tS 

t~  o  ^  in 

O    t»    05    ^ 

S5 

CO  in  «o  •«» 

r»  t~  t~  t- 

^ 

H 

8 

>> 

CO    05    OS    00 

O   00   00   -H 

E 

3 

00  CO  '-«  o 

'Jl    ^    t>    00 

gS?Kg 

►^ 

d 

« 

c; 
'^c; 

IN 

^     ^ 

--    CO    O    IN 

M-  OS  m  00 

e2 

O    t^    CO    « 

OS    00    00    X 

h 

>v 

•B 

00  00  ^  to 

(N  CO  in  — 

E 

K 

1^ 

03 

y 

t-  in  in  0- 

CO  o  CO  00 

•*  CO  e^  •<t 

(^  in  in  in 

H 

■^ 

3 

5 

■"B 

■c 

-n       1 

T3 

Tl       ■     rt       1 

V>  j=  'c 

lll> 

'  nil 

.S-^  £=j 

=  -S£? 

> 

!r 

C 

U 

> 

» 

C 

a 

642  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

is  due  probably  to  the  stronger  radiation  of  heat  from  the  ground  on  the 
uphill  side  against  the  trunk. 

Specific  Influence  on  Fruit  Growing. — These  data  indicate  that  south- 
ern and  eastern  slopes  are  preferable  for  the  production  of  fruits  for  the 
early  markets  or  for  any  fruit  or  variety  with  which  hastened  maturity 
is  an  important  consideration.  Thus  in  New  England  there  are  many 
locations  where  certain  varieties  of  grapes  can  be  ripened  properly  only 
when  grown  in  sheltered  spots  with  a  southern  exposure.  Often  there 
is  a  difference  of  a  week  or  more  in  the  maturing  seasons  of  the  same 
variety  on  the  northern  and  southern  sides  of  the  same  hill,  equivalent 
to  a  location  many  miles  southward  or  northward.  On  the  other  hand 
northern  and  western  slopes  are  preferable  when  delayed  maturity  is  the 
object.  Fruits  of  certain  species  like  the  apple  and  peach  are  likely  to 
be  somewhat  higher  colored  on  southern  than  on  northern  slopes.  It 
should  be  noted  that  late  spring  and  early  fall  frosts  are  no  more  likely 
to  occur  on  one  slope  than  on  another  and  that  consequently  more 
trouble  from  spring  frosts  at  least  will  be  encountered  on  southern  than 
on  northern  slopes  because  vegetation  starts  earlier  on  the  former.  It  is 
probably  on  this  account  mainly  that,  for  general  fruit  growing,  a  northern 
exposure  is  preferred  by  most  growers.  Areas  with  eastern  and  western 
exposures  are  intermediate  in  the  qualities  mentioned  between  those  with 
northern  and  southern  exposures.  Western  and  southwestern  slopes 
are  perhaps  least  desirable  under  average  conditions  and  with  most  fruits 
because  of  the  action  of  the  sun  and  of  temperature  in  causing  sunscald 
on  the  west  and  southwest  sides  of  the  trunk. 

Without  doubt  too  much  importance  is  attached  by  many  to  the 
advantages  or  disadvantages  offered  by  particular  exposures — at  least  as 
these  exposures  have  a  direct  bearing  on  tree  and  fruit  through  a 
modification  of  temperature  and  light  conditions.  In  the  great  majority 
of  cases  the  grower  can  raise  fruit  successfully  on  any  and  all  slopes,  pro- 
vided they  are  not  unreasonably  steep  and  have  suitable  soils.  It  may  be, 
and  often  is,  desirable  to  plant  certain  slopes  with  fruits  of  one  kind  or  one 
variety  and  other  slopes  with  other  kinds  or  other  varieties,  so  that  the  ad- 
vantages offered  by  the  different  exposures  may  be  fully  utilized.  Thus 
early  strawberries  might  be  grown  on  the  south  and  east  sides  of  a  hill 
and  midseason  and  late  varieties  on  its  west  and  north  sides  and  the  har- 
vesting season  thereby  lengthened  a  week  at  each  end.  The  idea  that 
one  slope  is  always  best  for  a  certain  fruit  or  a  certain  variety  is  erroneous. 
Much  depends  on  where  and  for  what  special  purpose  that  variety  is 
grown. 

Indirect  Effects. — There  are  certain  indirect  influences  of  slope  or 
exposure  on  the  growth  of  trees  and  their  maturing  of  a  crop  that  are  of 
importance  equal  to,  or  greater  than,  that  of  the  more  direct  influences. 
Southern  and  western  slopes  dry  out  more  rapidly  and  are  more  subject 


ORCHARD  LOCATIONS  AND  SITES  643 

to  drought  than  others.  Fruit  grown  on  northern  or  eastern  slopes 
therefore  tends  to  average  somewhat  larger  in  size  than  that  produced 
on  a  southern  or  western  exposure.  In  some  sections  the  soil  on  many 
southern  slopes  is  much  thinner  than  that  on  northern,  eastern  or  western 
exposures  and  in  such  instances  a  particular  slope  is  to  be  avoided,  not 
because  of  the  slope  itself  but  because  of  the  factors  with  which  it  is  asso- 
ciated. In  much  the  same  way  certain  slopes  are  to  be  avoided  in  certain 
sections  because  of  their  exposure  to  prevailing  winds.  When  land  slopes 
away  from  the  direction  of  the  prevailing  wind  considerable  protection 
is  afforded  the  trees  by  the  contour  of  the  ground,  but  when  it  slopes  in 
the  direction  of  the  prevailing  wind  much  more  trouble  is  likely. 

Abruptness  of  Slope. — Gentle  slopes  are  almost  always  preferable  to 
abrupt  slopes.  Many  orchards  on  very  steep  hillsides  have  proved 
profitable,  but  the  cost  of  production  under  such  conditions  is  likely  to 
be  considerably  higher  than  on  more  nearly  level  land  of  the  same  char- 
acter. This  of  course  assumes  equally  good  soil  and  other  conditions  on 
the  steep  and  the  gentle  slopes.  Different  environmental  conditions  in 
the  two  locations  may  reverse  the  situation.  Thus,  in  the  Piedmont 
section  of  Virginia  where  the  orchards  are  planted  on  steep  hillsides  and 
where  it  is  necessary  to  spray  five  to  seven  times,  apples  are  produced  at 
a  lower  cost  than  in  the  Shenandoah  valley  where  less  spraying  is  required. 
As  a  rule  it  is  best  to  limit  orchard  planting  to  slopes  so  gradual  that  cul- 
tivation may  be  practiced  without  great  danger  from  erosion  and  over 
which  spraying  machinery  and  other  equipment  may  be  hauled  without 
serious  difficulty.  The  necessity  of  gentle  slopes  is  still  greater  in  sections 
where  irrigation  is  practiced. 

AIR  DRAINAGE 

Fruit  growing,  more  than  almost  any  other  branch  of  agriculture, 
requires  comparative  freedom  from  untimely  late  spring  and  early  fall 
frosts;  in  turn  the  occurrence  of  frosts  within  certain  limits  is  determined 
largel}^  by  what  is  commonly  known  as  "air  drainage,"  the  settling  of 
cold  air  to  lower  levels.  This  is  discussed  in  some  detail  in  the  section  on 
Temperature  Relations. 

Influence  of  Elevation. — Many  factors  influence  air  drainage,  some 
to  a  very  marked  extent  and  others  only  to  a  comparatively  small  degree. 
Probably  the  most  important  single  factor  in  air  drainage  is  elevation. 
Height  above  adjoining  land  or  fields  usually  is  of  greater  significance 
than  absolute  elevation  above  sea  level.  Frost  is  as  likely  to  occur  during 
the  danger  period  at  the  high  elevations  found  in  some  of  the  intermoun- 
tain  fruit  growing  districts  as  at  the  low  elevations  of  the  seaboard. 
Portions  of  the  Ozarks  with  an  elevation  of  over  1,000  feet  are  as  frosty 
as  the  Hudson  River  valley,  which  lies  only  a  little  above  sea  level. 


644 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


However,  as  a  rule,  low  lying  land  is  more  subject  to  frost  than  that 
somewhat  elevated  above  surrounding  or  adjoining  fields,  though  there 
are  certain  exceptions  which  are  discussed  later. 

The  dilTerence  in  temperature  between  two  points,  one  of  which  is 
50  or  100  feet  above  the  other,  of  course  depends  on  many  factors,  such 
as  general  lay  of  land,  relative  areas  of  the  land  having  the  respective 
elevations  and  proximity  to  bodies  of  water.  However,  the  inequality 
in  temperature,  particularly  on  quiet  nights,  in  spring  and  fall  when 


64^ 


% 

\  ' 

>--v" 

Vv" 

/ 

\ 

An,. 

ATI 

'-•;'"• 

V 

..•-V'-' 

•''       r 

/    i 

v 

V 

V 

,r-' 

'A       / 

^ 

'\ 

TemperafureBSSfiabovehsesfc 

»           50.,      „      >'     " 

^J\              "         at  base  station. 

11 

\ 

^/~w^ 

ll 

V 

v..^ 

.  f-'^^ 

1 

j 

^ 

^^ 

1 

2P.M.  4P.M.  6P.M.  8P.M,  10P.M.  MDT.  Zh.M.  4AM.  6A.M.  8A.M.  10A.M. 
Fig.  67. — Continuous  records  of  the  temperature  from  4  p.  m.  to  9  a.  m.  at  the  base  and 
at  different  heights  above  the  base  of  a  steep  hillside,  showing  the  great  differences  in 
temperature  that  sometimes  develop  on  a  clear,  still  night.  Although  the  temperature  at 
the  base  was  low  enough  to  cause  considerable  damage  to  fruit,  the  lowest  temperature 
225  feet  above  on  the  slope  was  only  51°F.  Note  that  the  duration  of  the  lowest  tempera- 
ture was  much  shorter  on  the  hillside  than  at  the  base.     (After  Batchelor  and  West"^) 

there  is  greatest  danger  from  frost,  between  points  only  a  few  dozen  feet 
apart  in  elevation  is  often  considerable — often  enough  to  make  the 
difference  between  no  frost  or  a  very  light  frost  and  a  killing  frost.  Fig- 
ure 67  shows  graphically  the  diversity  in  minimum  temperature  that 
sometimes  occurs  with  variations  in  elevation  of  25,  50  and  225  feet. 
In  this  case  a  disparity  of  only  25  feet  in  elevation  was  accompanied 
by  a  difference  of  approximately  5°F.  between  8:00  p.m.  and  8:00  a.m. 
and  an  inequality  of  50  feet  was  accompanied  by  a  variation  of  15° 
to  20°F.  At  greater  elevations  the  temperature  was  still  higher,  though 
its  rise  was  not  proportional  to  the  increase  in  height. 

This  suggests  that  extreme  divergencies  in  altitude,  therefore,  are 
likely  to  afford  much  greater  security  from  frost  than  moderate  differences, 
very  slight  inequalities,  even  of  only  a  few  feet,  often  are  associated  with 
a  sufficient  variance  in  temperature  to  result  in  crop  safety  or  crop  loss. 
Perhaps  more  nearly  average  differences  in  minimum  temperature  due 


ORCHARD  LOCATIONS  AND  SITES 


645 


to  elevation  are  shown  in  Fig.  68.  These  graphs  represent  temperature 
variations  on  comparatively  still,  clear  nights  at  stations  in  a  mountain 
valley  during  the  blossoming  period  of  fruits.  Though  the  minimum 
temperature  was  not  invariably  recorded  at  the  lowest  elevations,  on 
each  of  the  four  nights  when  there  was  danger  from  frost  the  higher 


55 


S  40 


20 

1914-  f  '^^ 
April 


/ 

\ 

'^ — 

/ 

\ 

1 

pz"^ 

\ 

t 

4 

,  \ 

\ 

[ 

\ 

V  \ 

■^ 

u 

( 

\A 

\ 

n 

1 

V\ 

^ 

\ 

tl 

.-' 

M 

^ 

r-^ 

ij 

,- 

'.     > ' 

'\"~v. 

v^ 

tl  / 

y 

^    \ 

\ 

^v^ 

\ 

'III 

'^    V 

V, 

\  N 

\ 

r'<' 

I 

^' 

^^ 

\ 

\^ 

1 

^ 

\ 

/ 

A 

'■! 

\     '• 

A 

/ 

V 

^\ 

M 

/ 

/ 

•  \ 

^--' 

■.   \ 

1  1 

\ 

/ 

V 

v 

/ 

^\ 

\ 

.    '\ 

;  ■ 

\ 

/ 

■'vi, 

/ 

II 

\ 

f 

^ 

I 

^ 

/ 

y 

/ 

,11 

1 

\ 

/ 

/ 

/ 

It'll 

\ 

1 

'> 

/ 

/- 

i 

V 

/ 1 

(I 

/'  ' 

/  / 

/i 

/'( 

M 

\\ 

i^/ 

1 

' 

/ 

i? 

^^ 

\ 

/ 

Tde^.4791' 

Udev.4674'   - 

Velev.4561'   - 

Wek^/.4497' 

Xelev.44ez'  . 

\V 

1 

^■' 

>^\ 

'f 

\ 

\^^ 

H 

\ 

' 

\'\ 

:l 

•\ 

1 

\^ 

V 

1 

12      13      14 


ZQ    21     «    24    25     26    27 


16     n 
May 

Fig.  68. — The  daily  minimum  temperatures  for  stations  of  different  elevations  extend- 
ing from  the  high  agricultural  land  to  the  lowest  agricultural  land  of  the  valley.  {After 
Batchelor  and  West^} 

elevations  registered  temperatures  above  the  probable  danger  point 
and  a  fruit  crop  on  the  lower  levels  probably  would  have  been  destroyed. 
"The  minimum  temperatures  experienced  by  the  bench  lands  and  upper 
slopes  of  the  tillable  area  in  a  mountain  valley  average  from  6  to  10°F. 
warmer  than  the  valley  bottoms  due  to  the  drainage  of  cold  air  to  the 
low  areas  during  the  typical  clear,  calm,  frosty  nights.  "^  On  calm  but 
cloudy  nights  the  variation  in  minimum  temperatures  between  high 
and  low  points  in  this  valley  is  reduced  to  about  40  per  cent,  of  that 
on  calm,  clear  nights  and  during  windy  weather  there  is  very  little  differ- 
ence in  their  minimum  temperatures. 


646  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

The  point  should  be  emphasized  that  the  amount  of  air  drainage 
secured  by  selecting  a  site  somewhat  above  the  adjoining  fields  depends 
not  alone  on  the  amount  of  elevation,  but  also  on  the  area  from  which 
the  cold  air  drains  in  comparison  with  the  extent  of  that  to  which  it 
may  settle.  If  the  low  ground  upon  which  the  cold  air  may  sink  is 
limited  in  extent  and  has  little  outlet  while  the  area  to  be  drained  is 
large,  this  depression  will  soon  be  filled  with  cold  air  and  the  slope  above 
will  be  afforded  no  further  protection.  The  case  is  comparable  with  a 
large  watershed  supplied  with  an  inadequate  drainage  system.  An 
elevation  of  20  or  25  feet  above  a  wide  valley  may  thus  afford  better 
air  drainage  for  one  orchard  than  an  elevation  of  50  feet  above  a  narrow 
valley  affords  another.  In  many  cases  a  ravine  or  narrow  draw  along  one 
side  of  an  orchard  will  afford  a  given  site  better  air  drainage  than  an 
adjoining  low-lying  field  covering  many  acres,  provided  the  draw  or 
ravine  is  deep,  has  a  good  outlet  and  is  not  clogged  with  brush  and  timber 
that  interferes  with  free  movement  of  the  air.  In  other  words,  of 
two  areas  having  the  same  elevation  one  may  enjoy  much  better  air 
drainage  and  greater  freedom  from  frost  because  of  differences  in  the 
contour  and  topography  of  the  land  that  borders  them. 

The  graphs  in  Fig.  68  show  the  maximum  variations  in  temperatures 
during  the  night  between  stations  at  different  elevations  on  a  hillside. 
Though  day  temperatures  are  not  given  there  is  the  suggestion  that 
they  approximate  rather  closely.  Available  data  show  that  such  in- 
equalities in  elevation  as  are  normally  found  within  single  fruit  growing 
districts  are  responsible  for  but  small  differences  in  maximum  day 
temperatures. 2  In  other  words,  elevation  materially  influences  minimum 
and  average,  but  not  maximum,  temperatures. 

Thermal  Belts. — The  influence  of  elevation  on  air  drainage  and 
consequently  on  the  selection  of  sites  for  fruit  growing  should  not  be 
passed  over  without  a  reference  to  the  so-called  "thermal  belts,"  "ther- 
mal zones,"  "frostless  belts"  or  "verdant  zones,"  as  they  are  variously 
called.  They  are  comparatively  frost-free  belts  along  hillsides  or  mountain 
ranges,  below  and  above  which  frost  occurrence  is  not  uncommon.  The 
limits  of  comparatively  few  such  zones  have  been  accurately  mapped; 
consequently  the  fruit  industry  has  developed  more  or  less  independently 
of  them.  However,  their  occurrence  presents  an  interesting  phenomenon 
and  it  is  desirable  to  recognize  and  if  possible,  make  use  of  the  obvious 
advantages  they  provide,  for  without  doubt  the  fruit  growing  districts 
of  the  country  include  many  such  zones  that  are  not  being  utihzed  for 
fruit  production. 

The  following  quotations  from  an  article  by  Abbe^  will  point  out 
more  exactly  the  conditions  characteristic  of  thermal  belts : 

"Prof.  J.  W.  Chickering,  Jr.,  in  the  Bulletin  of  the  Philosophical  Society  of 
Washington,  March,  1883,  and  in  the  American  Meteorological  Journal,  Vol.  I, 


ORCHARD  LOCATIONS  AND  SITES  647 

describes  the  following  thermal  belt:  'In  Polk  County,  North  Carolina,  along 
the  eastern  slope  of  the  Tryon  Mountain  range,  in  latitude  north  35°,  the  thermal 
belt  begins  at  the  base  of  the  mountain,  at  an  elevation  of  1200  feet.  It  is 
about  8  miles  long,  and  is  distinguished  by  magnificent  flora,  such  as  would  be 
characteristic  of  a  point  3°  south  of  the  actual  latitude.' 

"Prof.  John  Leconte,  of  Berkeley,  Cahfornia,  in  Science,  Vol.  I,  p.  278,  states 
that  at  Flat  Rock,  near  Hendersonville,  Henderson  County,  North  Carolina,  on 
the  flank  of  the  mountain  spur  adjacent  to  the  valleys  of  the  Blue  Ridge,  he  also 
observed  a  frostless  zone.  The  valley  is  about  2200  feet  above  sea  level,  and 
the  thermal  belt  is  200  to  300  feet  above  the  valley. 

"J.  W.  Pike,  of  Vineland,  N.  J.,  states  that  among  the  mountains  of 
California  he  has  discovered  that  during  the  night  the  cold  is  much  greater  in 
the  valleys  than  on  the  terraces  several  hundred  feet  above,  due  to  the  settling 
of  the  cold  air,  so  that  a  thermal  belt  is  formed  at  that  height  separating  the 
frosty  valleys  from  the  colder  highlands. 

"In  the  Tennessee  Journal  of  Meteorology  for  January,  1894,  published  by  the 
State  Weather  Service,  the  author  describes  a  thermal  belt  between  Los  Angeles 
and  the  Pacific  Coast.  It  traverses  the  foothills  of  the  Cahuenga  range,  and 
has  an  elevation  of  between  200  and  400  feet  and  a  breadth  of  about  3  miles. 
It  occupies  the  midway  region  of  the  range. 

"In  the  American  Meteorological  Journal,  Vol.  I,  S.  Alexander  describes 
a  thermal  belt  in  which  the  peach  tree  flourishes  in  the  southeastern  portion  of 
Michigan.  He  shows  that  the  cold  island  discovered  by  Winchell  in  that  region 
is  really  the  bottom  of  a  topographical  depression  into  which  the  cold  air  settles. 
It  is  a  long  valley  surrounded  by  a  belt  of  elevated  country  from  50  to  600  feet 
above  Lakes  Michigan  and  Huron.  The  valley  and  the  isotherms  trend  north- 
east and  southwest  from  Huron  County  through  Sanilac,  Lapeer,  Oakland,  Liv- 
ingston, and  Washtenaw  to  Hillsdale  Counties.  The  highlands  of  this  region 
are  all  much  freer  from  frost  than  the  lowlands,  and  all  much  more  favorable  for 
early  vegetation.  He  does  not  state  that  any  point  is  high  enough  to  be  above 
the  thermal  belt,  but  that,  in  general,  two  equal  parallel  thermal  belts  inclose  the 
cold  island  between  them. 

"It  is  generally  conceded  that  these  thermal  belts  depend  both  upon  the 
drainage  of  cold  air  downward  into  the  lower  valleys  and  the  freedom  of  radiation 
from  the  surface  of  the  ground  to  the  clear  sky  overhead.  During  a  still  night, 
when  frosts  occur,  the  surface  of  the  hillside  cools  by  radiation,  and  hence  cools 
the  air  in  contact  with  it;  the  latter  flows  downward  as  long  as  its  cooling  by 
radiation  and  conduction  exceeds  its  warming  by  compression.  Inasmuch  as  its 
cooUng  depends  on  contact  with  a  still  colder  soil  or  plant,  it  soon  accumulates 
in  the  lowlands  as  a  layer  of  cold  air,  which  grows  thicker  during  the  night  by 
the  steady  addition  of  the  thin  layer  of  descending  air  in  contact  with  the  ground 
on  the  hillsides.  The  warmer  air,  which  has  not  yet  had  an  opportunity  to  cool 
by  contact  with  the  ground,  floats  on  top  of  the  cold  mass;  it  spreads  out  toward 
the  hills,  and  is  continuously  furnishing  its  heat  to  the  adjacent  hillsides  as  fast 
as  it  comes  in  contact  with  them  before  it  also  cools  and  descends.  The  formation 
of  the  thermal  belt  seems  to  depend  largely  upon  this  gentle  circulation  during 
the  night  time.  1  he  lower  limit  of  the  belt  is  defined  by  the  depth  of  the  accumu- 
lation of  cold  air  in  the  confined  valley  and  rises  higher  in  proportion  as  the  night 


648  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

is  clearer  and  longer,  and  also  in  proportion  as  the  valley  is  more  or  less  perfectly- 
inclosed.  The  upper  limit  of  the  thermal  belt  may  depend  upon  the  strength  of 
the  wind,  and  the  general  temperature  of  the  air.  But  if  there  be  no  wind,  then 
it  depends  equally  on  the  freedom  of  radiation  to  the  clear  sky  and  on  the  above- 
described  circulation  of  air." 

Influence  of  Bodies  of  Water. — After  elevation,  probably  the  next 
most  important  factor  influencing  air  temperature  and  drainage  is 
proximity  to  bodies  of  water.  The  specific  heat  of  water  is  high;  it 
absorbs  heat  slowly  and  gives  it  up  slowly.  Consequently  in  the  spring 
a  large  body  of  water  warms  more  slowly  and  in  the  fall  it  cools  more 
slowly  than  the  surface  of  the  adjacent  land  or  than  near  by  vegetation. 
It  is  slower  even  than  the  atmosphere  in  responding  to  changes  in  tem- 
perature. Relatively  the  air  shows  a  great  variation  in  temperature 
between  night  and  day,  while  a  body  of  water  of  considerable  size  shows 
no  appreciable  change.  The  air  warmed  during  the  day,  coming  in 
contact  with  the  surface  of  a  body  of  water,  is  cooled;  consequently  the 
air  in  close  proximity  to  such  a  body  is  cooler  than  it  would  be  otherwise. 
On  the  other  hand,  at  night  air  cooled  to  a  temperature  below  that  of 
the  water,  is  warmed  by  contact  with  its  surface  and  in  turn  gives  up 
that  heat  to  vegetation  and  other  bodies  with  which  it  comes  in  contact. 
Consequently  points  close  to  bodies  of  water  are  frequently  somewhat 
cooler  during  the  day  and  warmer  at  night  than  corresponding  inland 
points  and  are  freer  from  frosts,  while  blossoming  is  at  the  same  time 
retarded  in  their  proximity. 

Influence  of  Distance  from  Water. — Some  measure  of  this  influence 
may  be  obtained  from  data  presented  in  Table  12  showing  the  air  tem- 
peratures, atmospheric  humidity  and  dewpoints  for  three  stations  in 
New  Jersey  and  one  on  Kelley's  Island  in  Lake  Erie  for  the  months  of 
July  and  August,  1866.  Vineland  is  about  30,  Haddonfield,  50  and 
Greenwich  5  miles  from  the  ocean,  or  from  wide  ocean  tributaries,  while 
Kelley's  Island,  as  the  name  indicates,  is  surrounded  by  water.  The 
daily  range  of  temperature  is  higher  the  farther  the  station  is  removed 
from  the  influence  of  water  and  also  the  more  remote  the  station  the 
lower  is  its  mean  atmospheric  humidity  and  the  lower  its  mean  dewpoint. 
In  other  words,  those  stations  close  to  large  bodies  of  water  enjoy  a 
climate  more  equable  in  temperature  and  consequently  less  subject  to 
frost  injury. 

The  interchange  of  heat  and  equalization  of  temperature  in  the 
vicinity  of  bodies  of  water  is  favored  by  a  gentle  breeze  but  it  will  occur 
to  a  certain  extent  when  there  is  practically  no  air  stirring  at  inland 
points.  The  water  is  itself  responsible  for  a  certain  amount  of  air  move- 
ment and  the  attendant  air  drainage.  It  is  almost  needless  to  state  that 
the  larger  the  body  of  water  the  greater  is  its  influence  on  air  movement 
and  air  temperature.     Much,  too,  depends  on  the  topography  in  the 


ORCHARD  LOCATIONS  AND  SITES  649 

immediate  vicinity  of  the  body  of  water.  For  instance,  the  so-called 
*' fruit  belt"  on  the  eastern  shore  of  Lake  Michigan  varies  in  width  from 
less  than  2  to  over  20  miles.  The  lake  is  as  wide  where  the  belt  is  narrow 
as  where  the  belt  is  wide,  but  the  lay  of  the  land  is  quite  different.  As  a 
rule  but  little  influence  of  the  water  is  felt  back  of  the  crest  of  the  slope 
toward  the  lake,  bay  or  river  and  frequently  its  influence  does  not  extend 
to  the  crest  of  the  slope.  Naturally,  if  the  slope  is  gradual  the  influence 
is  likely  to  be  felt  further  back  than  if  it  is  abrupt. 

Influence  of  Size  and  Shape  of  Body  of  Water. — Something  of  the 
relation  between  the  size  of  the  body  of  water  and  that  of  the  area 
influenced  by  it  may  be  understood  by  comparing  the  width  of  the  fruit 
belts  bordering  Lake  Michigan  or  Lake  Ontario  with  those  bordering 
Lakes  Seneca  or  Canandaigua  in  New  York.  As  already  stated,  the 
Michigan  fruit  belt  is  from  2  to  20  miles  wide.  The  fruit  belt  along 
Lake  Ontario  is  of  equal  width.  Lakes  Seneca  and  Canandaigua,  them- 
selves only  about  4  miles  wide  at  the  most,  have  distinct  fruit  belts  only  a 
quarter  of  a  mile  to  2  miles  in  width.  A  deep  body  of  water  has  a  much 
greater  influence  on  the  climate  of  the  adjoining  land  than  one  which  is 
shallow.  The  water  is  in  effect  a  heat  sponge,  absorbing  heat  whenever 
air  temperatures  rise  above  the  mean  and  liberating  heat  whenever  they 
fall  below  it.  Naturally,  then,  the  larger  this  sponge  the  greater  is  its 
absorbing  and  liberating  capacity.  This  is  particularly  important  in 
the  case  of  bodies  of  water  so  deep  that  they  seldom  freeze  over  or 
remain  frozen  for  only  a  short  time,  as  it  relates  to  their  modifying 
influence  on  midwinter  minimum  temperatures.  On  the  other  hand 
many  lakes  as  wide  as  the  finger  lakes  of  central  New  York,  because  they 
are  very  shallow,  furnish  little  protection  to  the  neighboring  slopes. 
Protection  is  likely  in  the  vicinity  of  large  rivers,  especially  if  they  are 
deep.  Their  currents,  which  delay  or  prevent  their  freezing  over,  may 
partly  compensate  for  their  lack  of  depth;  a  river  10  to  20  feet  deep  and  a 
quarter  of  a  mile  wide  may  afford  as  much  protection  to  orchards  along 
its  course  as  a  lake  twice  that  depth  and  of  the  same  width.  Indeed  it  is 
likely  to  afford  greater  protection  because  of  its  channel  down  which  the 
cold  air  may  continue  to  drain  indefinitely. 

Indirect  Ternperature  Effects. — Bodies  of  water  influence  temperatures 
in  their  vicinities  in  other  ways  than  through  promoting  air  drainage. 
There  are  certain  favored  spots  where  the  increased  atmospheric  humidity 
due  to  proximity  of  water  leads  to  the  frequent  formation  of  fog  during 
periods  when  dangerously  low  temperatures  occur  at  nearby  points  and 
a  very  effective  check  is  thus  placed  on  loss  of  heat  by  radiation. 
Kelley's  Island  in  Lake  Erie  has  been  noted  as  a  place  thus  rendered 
especially  suited  to  the  culture  of  comparatively  tender  long-season 
fruits  and  without  doubt  this  is  one  of  the  chief  factors  in  making  possible 
the  successful  culture  of  European  plums  in  the  vicinity  of  Ste.  Anne  de 


650 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


Beaupr^  in  Quebec,  200  miles  north  of  the  general  northern  limit  for  the 
same  varieties. 

Probably  it  would  be  difficult  to  separate  entirely  the  different 
influences  of  bodies  of  water  upon  climate,  assigning  to  air  drainage  or  to 
increased  atmospheric  humidity  exact  figures  representing  their  pro- 
tective effects.  The  fact,  however,  that  these  other  protective  influences 
are  at  work  does  not  lessen  in  importance  the  air  drainage  that  is  asso- 
ciated with  water  surfaces. 

Minor  Temperature  Effects. — Even  small  bodies  of  water  have  meas- 
urable, though  slight,  influences  on  temperature.  Observations  of  mini- 
mum temperatures  near  a  stream  40  feet  wide  in  England,  summarized 
in  Table  13,  show  that  the  extent  of  the  influence  varies. 


Table  13.- 


-AvERAGE  Minimum  Temperatures  (Centigrade)  At  and  Near  River 
Bank^o 


(Six  inches  above  ground) 

Station  6,  196 

Station  8,  on  river 

Station  7,  on  river 

bank  (confluence 

of  river  and 

ditch),  degrees 

feet  from  river, 
degrees 

bank  (straight 
part),  degrees 

Minimum  all  nights 

2.2 

3,0 

3.3 

Excess  on  river  banks 

0,8 

1.1 

Minimum  still  nights 

0.0 

0,9 

1.4 

Excess  on  river  banks 

0.9 

1.4 

Minimum  nights  with  south 

or  southeast  wind 

3.5 

4.4 

5.4 

Excess  on  river  banks 

0.9 

1.9 

Minimum  nights  with  north 

or  northeast  wind 

1.6 

2,0 

2.5 

Excess  on  river  bank 

0.4 

0  9 

Importance  during  the  Winter.^ — Attention  has  been  called  particularly 
to  the  effects  of  air  drainage  on  temperature  during  the  soring  and  fall 
months  and  its  bearing  on  the  occurrence  of  frosts.  It  should  not  be  in- 
ferred, however,  that  air  drainage  does  not  take  place  during  other  sea- 
sons where  elevation  and  topography  make  it  possible.  Figures  69  and 
70  show  differences  in  minimum  temperatures  during  some  of  the  winter 
months  between  stations  at  unequal  elevations  in  a  mountain  valley  in 
Utah.  These  range  between  2°  and  8°F.  on  the  coldest  nights  for  stations 
having  64  feet  disparity  in  elevation  and  are  about  10°  for  stations  having 
350  feet  variance  in  altitude.  Such  differences  in  minimum  temper- 
atures during  midwinter  may  often  influence  the  amount  of  certain  kinds 
of  winter  injury  or  winter  killing  experienced.  Air  drainage,  therefore,  is 
sometimes  of  as  great  importance  in  preventing  winter  injury  as  it  is  in 


ORCHARD  LOCATIONS  AND  SITES 


651 


warding  off  injury  from  late  spring  or  early  fall  frosts.  Indeed,  there  are 
certain  sections  in  which  and  certain  fruits  with  which  elevation  to  secure 
air  drainage  is  of  greater  importance  in  dealing  with  midwinter  freezing 
than   with   spring   frost.     The   bark   and   trunk   splitting   occasionally 


30 


Fig. 


0 
I9I4  20 


/ 

/ 

/ 

/ 

/ 

/ 

/ 

\ 

/ 

/ 

\ 

/ 

/ 

^^^ 

/ 

/ 

N    / 

N 

v/ 

\ 

■^ 

\ 

•V 

/ 

\ 

^ 

/ 

\ 

w 

/ 

\ 

/ 

1 

\ 

/ 

/ 

'--. 

1 

\ 

/ 

-  / 

/ 

V 

^1 

1;/ 

?! 

■^1 

\ 

4' 

\ 
\ 

-i 

\ 

\ 

1 

\ 
\ 

1 
1 

'^>.^  J 

1 

n 


25         24         26 
November 


27 


?8 


). — The  minimum  daily  temperature  for  a  bench  land  and  a  valley  bottom 
station  during  9  clear,  autumn  nights.      {After  Batchelor  and  West'^) 


accompanying  sudden  midwinter  drops  in  temperature  in  the  compara- 
tively mild  climate  of  the  Willamette  valley  is  a  case  in  point. 

Obstructions. — Air  drainage  is  often  impeded  more  or  less  seriously 
by  obstructions  of  one  kind  or  another,  such  as  a  stone  wall,  a  hedge  or  a 
high  board  fence,  a  mass  or  belt  of  shrubbery.     Thus  it  happens  that  a 


652 


FUNDAMENTALS  OF  FRUIT  PRODUCTION 


natural  or  artificial  planting  sometimes  serving  admirably  as  a  wind  break 
and  protecting  the  orchard  at  certain  seasons,  hinders  air  movement  on 
calm  nights  to  such  an  extent  that  little  of  the  frost  protection  naturally 
expected  from  the  orchard's  elevation  is  actually  obtained.  No  rules  can 
be  given  for  dealing  effectively  with  these  hindrances  to  air  drainage,  but 
the  whole  question  should  be  considered  on  the  ground  when  selecting  an 
orchard  site. 


\ 

N~~l 

1 

\ 

1 

\ 

1 

1 

\ 

1 

/-/ 

1 1  i 

/   / 

\ 

/  ^  \ 

_      J   J. 

\ 

/  /  il 

1 

\ 

1       A 

— /— 
f 

|\ 

1     \ 

J     / 

\ 

^J 

1 

/ 

\ 

'^ 

/ 

\ 

^ 

/         ' 

w 

IkU 

.§ 

,          \ 

r 

1 

Jjtvifi 

m 

l4iT,-^G 

, 

1 

■cs 

tl\\^ 

^      i 

l' 

' 

'        \ 

/    1^ 

SI 

I 

' 

-2 

'    \ 

H^ 

I 

fe 

I     ^   ' 

i  'J 

i  \ 

E       3 

\ 

'■< 

\\ 

1 

r    r      / 

I      I 

\\ 

3            / 

/       \ 

^ 

\ 

§         T 

/       \ 

r 

\ 

£      i_l 

'        \ 

1 

\  \ 

\\ 

/ 

o  -L 

\\ 

/ 

N       ' 

°  / 

\\ 

/ 

\ 

» 

\ 

\  ( 

I 

^-' 

\       . 

1 

\     ' 

r 

\    ' 

6  p 

>  1 

t~ 

N 

-q- 

11    II 


24       25       26        Z1       28        23       30       31      .    I  2 

December,  1913  Januaa),l914 

Fig.  70. — Minimum  temperatures  for  stations  of  different  elevations  during  12  clear, 
calm,   winter  nights.      (After  Batchelor  and   West'^) 


LOCAL  VARIATIONS  AND  THEIR  SIGNIFICANCE 
Data  have  been  presented  showing  that  points  only  a  few  miles  apart 
sometimes,     because    of    topographic     pecuharities,     present    climatic 
differences  great  enough  to  be  of  considerable  importance  in  fruit  growing. 


ORCHARD  LOCATIONS  AND  SITES 


653 


The  magnitude  of  such  disparities  often  found  between  points  on  the 
same  farm  and  occupying  positions  differing  Uttle  in  elevation  or  exposure, 
is  not  appreciated.  Their  influence  is  often  subtle,  but  nevertheless  real. 
They  may  make  the  difference  between  the  necessity  of  one  or  of  three 
applications  of  a  fungicide,  an  interval  of  a  week  in  the  time  of  partic- 
ular spray  applications,  or  of  a  week  in  the  blossoming  or  maturing  seasons 
of  a  fruit. 

Temperature. — It  is  not  the  intention  in  this  discussion  to  present 
further  data  on  the  influence  of  a  certain  number  of  "heat-units"  in 
bringing  to  particular  stages  of  maturity  plants  of  different  kinds. 
However,  mention  may  be  made  of  the  variation  in  the  mean  temperature 
between  stations  only  a  short  distance  apart.  MacDougaH^  presents 
data  showing  that,  of  two  stations  in  the  New  York  Botanic  Garden  only 
a  few  hundred  yards  apart  and  presenting  no  great  difference  in  elevation, 
one  received  78,836  hour-degrees  of  heat  in  1  year  and  the  other  only 
68,596.  One  of  these  points  registered  a  temperature  below  freezing 
during  1478  hours  in  the  course  of  the  year  and  the  other  during  1736 
hours.  Here  is  a  difference  of  13  per  cent  in  heat  units;  in  other  words, 
one  station  enjoyed  a  temperature  that  was  equivalent  to  an  active  grow- 
ing season  of  about  11  days  longer  than  the  other.  Such  a  disparity  is 
large  enough  to  account  for  the  difference  between  success  and  failure 
with  many  fruit  crops,  as  for  instance  grapes,  along  the  northern  limits 
of  their  cultural  range  and  it  shows  the  importance  to  the  grower  of  study- 
ing carefully  the  local  variations  often  found  within  the  limits  of  a  single 
farm. 

Equally  or  even  more  striking  are  the  figures  recording  the  temper- 
atures of  two  stations  on  the  campus  of  the  University  of  California  at 


Table  14. — Showing  Variations  in  Temperature  Between  Two  Stations  on 
THE  Campus  of  the  University  of  California^ 

Month 

Mean 
monthly  maximum 

Mean 
monthly  minimum 

Maximum 

Minimum 

- 

B 

A 

B 

A 

B 

A            B 

September,  1902 

79.3 
62.3 
70.8 
74.5 
75.6 
77.4 
76.6 
66.7 
76.2 
80.5 

71.4 
62.0 
66.9 
73.4 
70.0 
69.6 
70.2 
64.5 
70.0 
71.7 

54.5 
36.8 
43.1 
49.7 
50.0 
48.2 
48.3 
42.5 
45.8 
47.9 

55.  8 
44.7 
48.3 
52.3 
52.0 
51.9 
52.2 
46.5 
49.4 
51.3 

94 
74 
84 
108 
100 
86 
102 
88 
92 
98 

83.2 
70.0 
79.1 
101.1 
94.0 
78.9 
91.7 
82.9 
85.3 
92.8 

48 
32 
34 
36 

44 
44 
44 
34 
38 
42 

49.0 
36.6 

May,  1903     

42.6 

June,  1903     

42.4 

July,  1903 

46.8 
49.0 

September  1903 

April,  1904          

46.0 
37.2 

May,  1904     

40.6 

June,  1904       

48.2 

73.4 

09.0 

46.7 

50.4 

92.6 

85.9 

39.0 

43.8 

654  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Berkeley,  presented  in  Table  14.  Though  these  stations  were  120  feet 
apart  in  elevation,  elevation  alone  cannot  be  held  responsible  for  the 
differences  recorded,  for,  as  mentioned  elsewhere,  the  influence  of  ele- 
vation on  mean  temperature  amounts  to  only  4°F.  for  each  1000  feet. 
Without  doubt  many  factors  contribute  to  these  local  variations  in  tem- 
perature, some  being  more  important  in  one  case  and  others  in  another. 
It  is  not  so  important  that  all  these  factors  be  known  and  exactly  evaluated 
in  every  instance  as  it  is  that  their  combined  effect  be  recognized  and 
properly  utilized. 

Evaporation,  Rainfall  and  Other  Factors. — It  is  generally  recognized 
that  some  spots  or  some  locations  are  more  subject  than  others  to  the 
drying  action  of  the  wind;  however,  the  extent  and  importance  of  differ- 
ences in  this  respect  are  not  generally  recognized.  Gager^^  records  results 
of  evaporimeter  experiments  in  the  New  York  Botanic  Garden  in  1907  that 
are  particularly  interesting.  Three  specially  constructed  evaporimeters 
were  placed  at  several  points  in  the  garden ;  one  was  on  a  dry  rocky  knoll 
partly  shaded  by  trees;  a  second  was  on  low,  poorly  drained,  marshy 
ground,  also  partly  shaded  and  the  third  was  in  the  open  on  well  drained 
ground  with  sod  on  the  one  side  and  cultivated  ground  on  the  other.  The 
evaporation  losses  from  these  different  instruments  between  June  3  and 
October  14  were  equivalent  to  8.47,  4.84  and  12.10  inches,  respectively. 
The  precipitation  during  the  same  period  was  9.32  inches.  At  the  first 
station  precipitation  exceeded  evaporation  loss  by  only  0.85  inch,  at  the 
second  station  by  4.48  inches,  while  at  the  third  station  the  evaporation 
loss  exceeded  precipitation  by  2.78  inches.  In  commenting  on  these 
data,  Gager  says:  "It  should  be  kept  in  mind  that  the  loss  of  water 
from  the  evaporimeters  is  not  a  measure  of  the  amount  of  water  lost  by 
the  soil  through  evaporation,  but  it  is  only  an  index  of  the  evapor- 
ating power  of  the  air  for  the  given  station.  For  the  same  locality  the 
rate  of  evaporation  from  soil  and  from  evaporimeter  will  materially 
differ,  being  less  from  soil  and  varying  with  its  nature  and  condition,  as 
well  as  with  the  surroundings  above  the  soil  surface."  Nevertheless  at 
one  station  the  evaporation  losses  were  between  two  and  three  times  those 
at  one  of  the  others  and  such  a  difference  may  often  be  enough  to  have  a 
great  influence  on  plant  growth  and  crop  yield. 

Local  variations  in  rainfall  are  likely  to  be  especially  large  in  sections 
showing  considerable  difference  in  elevation,  but  they  are  often  important 
where  the  elevations  are  substantially  the  same.  Thus  at  Davis,  Cali- 
fornia, when  the  annual  rainfall  was  16  inches,  it  was  about  25  inches  at 
a  point  ten  miles  to  the  west  and  having  the  same  elevation.  Thirty 
miles  still  further  west,  but  in  the  foothills  of  the  Coast  Range,  it  was 
over  50  inches. 

With  the  local  variations  in  temperature  and  humidity  there  are  often 
important  differences  in  the  prevalence  of  insects  and  diseases  that., 


ORCHARD  LOCATIONS  AND  SITES  655 

independent  of  direct  influence  of  the  environment  on  the  plant,  may 
set  definite  Hmits  to  the  profitable  culture  of  certain  fruit  varieties. 

There  may  be  also  minor  local  variations  in  their  life  histories  which 
modify  the  effectiveness  of  spraying  treatments.  The  best  time  for  a 
certain  spray  in  one  neighborhood  may  differ  several  days  from  that  for 
another  neighborhood  not  far  away. 

Summary. — The  selection  of  a  location  for  fruit  production,  or  of 
kinds  and  varieties  of  fruit  to  be  grown  in  a  particular  location,  involves 
a  consideration  and  application  of  the  same  general  principles.  The 
more  important  economic  considerations  are  the  cost  of  land  and  the 
nearness  and  character  of  transportation  facilities.  The  overhead  charge 
due  to  cost  of  land  should  never  exceed  10  per  cent,  of  the  value  of  the 
product  at  the  orchard  and  should  not  amount  to  more  than  half  that 
figure.  The  cost  of  hauling  to  the  local  market  or  to  a  shipping  station 
should  levy  no  greater  tax  against  the  total  income.  Other  factors, 
such  as  fruit  product  establishments  and  cooperative  shipping  organiza- 
tions affecting  the  ability  to  dispose  of  products  quickly  and  advantage- 
ously are  important  in  commercial  production. 

Different  slopes  offer  quite  distinct  environmental  conditions  for 
the  growth  of  the  plant  and  certain  slopes  may  be  much  preferred  to 
others  for  certain  fruits  when  grown  in  some  sections,  though  the  reverse 
condition  may  hold  for  the  same  varieties  in  another  section.  These 
environmental  differences  can  be  profitably  capitalized  in  many  cases 
if  kinds  and  varieties  are  selected  so  as  to  obtain  the  closest  adaptation 
to  the  particular  farm  or  parts  of  the  farm.  The  same  may  be  said  of 
minor  inequalities  in  temperature,  rainfall  and  evaporation  between 
near  by  points  that  possess  nearly  the  same  elevation  and  exposure. 

Factors  of  great  importance  in  determining  danger  from  late  spring 
and  early  fall  frosts  are  the  air  drainage  incident  to  unequal  eleva- 
tion and  the  proximity  to  bodies  of  water.  Often  comparatively  small 
disparities  in  elevation  (25  to  50  feet)  make  a  considerable  difference  in 
danger  from  frost  injury.  This  influence  is  important  also  in  determining 
the  amount  of  damage  from  midwinter  freezing.  Proximity  to  large 
bodies  of  water,  particularly  on  their  windward  side,  affords  considerable 
protection  from  extremes  of  climate.  The  range  of  influence  of  such 
bodies  of  water  varies  with  their  size  and  depth  and  with  the  topography 
of  the  adjoining  slopes. 


CHAPTER  XXXV 
ORCHARD  SOILS 

All  field  crops  are  influenced  more  or  less  by  the  kind  of  soil  in  which 
they  are  grown.  The  same  may  be  said  of  all  fruit  crops.  Just  as  some 
land  is  classed  as  good  for  general  crops  so  some  may  be  classed  as  good 
for  orchard  fruits  and  just  as  some  is  considered  good  for  wheat  but  poor 
for  alfalfa,  so  some  may  be  good  for  pears  but  poor  for  strawberries.  In 
a  way  the  factors  that  are  important  in  determining  the  value  of  a  particu- 
lar soil  for  field  crops  are  also  important  in  determining  its  value  for  fruit 
production.  However,  were  the  judging  of  soils  for  general  farming 
purposes  and  for  orcharding  to  be  placed  on  a  score-card  basis  the  cards 
would  differ  considerably  in  a  number  of  respects. 

For  field  crops,  both  surface  soil  and  subsoil  are  important  in  deter- 
mining relative  value  of  the  land  but  the  surface  soil  is  generally  regarded 
as  of  far  greater  importance.  For  fruit  crops  in  general  they  are  of  more 
nearly  equal  significance.  Indeed  there  are  many  conditions  presented 
in  which  there  is  little  doubt  but  that  the  nature  of  the  subsoil  is  more 
significant  than  that  of  the  surface  soil.  For  field  crops  physical  and 
chemical  conditions  are  generally  considered  of  substantially  equal 
importance  in  determining  productivity  and  suitability  to  individual 
crops.  Though  chemical  composition  is  likewise  important  in  the  produc- 
tion of  trees  and  other  fruit  plants,  physical  condition  is  a  first  considera- 
tion. The  fact  that  certain  fruits,  such  as  the  apple,  are  grown  with  equal 
success  in  some  of  the  heavy  clay  loams  of  western  New  York,  the  light 
sandy  loams  of  New  Jersey,  the  loess  bordering  the  Missouri  River,  the 
adobes  of  the  Rogue  River  valley,  Oregon  and  the  volcanic  ash  of  the 
Hood  River  section  of  Oregon  appears  to  contradict  this;  nevertheless 
closer  analysis  reveals  certain  common  characteristics  of  their  physical 
condition — a  similarity  much  greater  than  is  shown  in  a  comparison  of  their 
chemical  composition. 

CONSIDERED  FROM  THE  STANDPOINT  OF  PHYSICAL  CONDITION 

Chief  among  the  physical  characteristics  desirable  in  an  orchard 
soil  are  porosity  and  thorough  aeration,  coupled,  if  possible,  with  depth. 
The  loess  soils  of  the  Mississippi,  Missouri,  Rhine  and  Hoang-ho  val- 
leys are  among  the  best  in  the  world  for  the  fruits  that  will  grow  in 
the  climates  of  these  respective  regions  because  they  are  extremely  deep, 

656 


ORCHARD  SOILS  657 

drainage  is  practically  perfect  (the  water  table  often  being  50  or  more 
feet  below  the  surface)  and  they  are  so  well  aerated  that  tree  roots  often 
penetrate  to  a  depth  of  20  feet  and  ordinarily  to  depths  of  6,  8  or  10. 
In  the  Rhine  valley  grape  roots  have  been  traced  to  a  depth  of  15  meters. 
Similar  conditions  exist  in  some  of  the  volcanic  ash  soils  of  the  Pacific 
Northwest  and  the  alluvial  soils  and  bench  lands  of  many  river  valleys 
in  Washington,  Idaho,  Oregon  and  California.  One  of  the  main  reasons 
certain  of  the  arid  soils  of  California  have  proved  so  well  suited  to  fruit 
growing  is  that  the  surface  soil  grades  insensibly  into  the  subsoil  and 
that  the  latter  is  well  drained  and  thoroughly  aerated;  hence  roots 
penetrate  to  great  depths  and  sustain  the  plant  when  the  surface  soil 
may  become  too  dry.^^  That  good  drainage  and  its  corollary  good 
aeration  are  associated  with  this  condition  is  indicated  by  Hilgard^^ 
when  he  states  that  with  the  rise  of  the  water  table  in  such  soils  through 
injudicious  irrigation  trees  that  had  thrived  may  actually  suffer,  much 
as  those  planted  in  shallow  soil  or  soil  underlaid  with  an  impervious 
hardpan  and  from  practically  the  same  causes. 

The  extent  to  which  the  success  of  the  fruit  plantation  depends  on 
these  two  factors,  drainage  and  aeration,  is  not  generally  realized.  In 
speaking  of  the  soil  requirements  of  the  papaya  Higgins-^  says:  "There 
are  few,  if  any,  soils  in  which  the  papaya  will  not  grow  if  aeration  and 
drainage  are  adequately  supplied.  Most  of  the  plantings  of  this  Station 
are  upon  soils  regarded  as  unsuitable  for  other  fruit  trees,  and  upon 
which  the  avocado  is  a  failure.  .  .  .  They  are  very  porous,  permitting 
a  perfect  drainage  and  aeration."  The  same  writer  goes  so  far  as  to 
say,  "There  are  two  essential  features  of  a  good  banana  soil.  The 
first  is  abundant  moisture,  the  second,  good  drainage.  "^^  In  speaking 
of  the  soil  requirements  of  forest  trees  one  authority  maintains  that 
almost  any  soil  is  capable  of  producing  any  kind  of  timber  if  the  moisture 
requirements  are  satisfied. ^^  Even  the  blueberry,  which  is  often  classed 
as  a  semiaquatic  or  bog  plant,  requires  a  well  aerated  medium  for  its 
roots  and  does  not,  contrary  to  appearances,  send  them  down  into  the 
water  or  into  waterlogged  soil.^  Obviously,  certain  shallow  rooted 
species  such  as  the  strawberry  do  not  require  and  could  not  make  full 
use  of  a  soil  of  the  depth  best  suited  to  one  of  the  tree  fruits,  but  even 
the  strawberry  will  do  much  better  in  a  soil  that  is  moderately  deep 
(say,  two  and  one  half  to  three  feet)  and  well  drained  than  in  one  that  is 
shallow  or  poorly  drained  and  poorlj^  aerated. 

Requirements  of  Different  Crops. — However,  there  are  marked 
differences  between  species  and  even  between  varieties  of  the  same 
species  in  their  preferences  for  soils  of  unlike  textures.  The  peach 
and  almond  flourish  only  in  soils  of  a  comparatively  light  porous  texture, 
while  the  pear  and  quince  prefer  at  least  moderately  heavy  soils  and  will 
often  do  well  in  extremely  heavy  soils.     The  pomegranate  is  reported  as 


658  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

doing  fairly  well  in  soils  ranging  from  almost  pure  sand  to  heavy  clay, 
but  it  does  its  best  only  in  those  that  are  fairly  heavy  and  well  drained; 
however,  it  will  endure  a  wet,  poorly  aerated  soil  much  better  than 
most  fruit  plants. ^^  Probably  nowhere  in  the  world  does  the  pineapple 
do  better  than  along  the  east  coast  of  Florida,  between  Fort  Pierce  and 
Lake  Worth,  where  the  soil  is  almost  a  pure  white  sand  (containing 
actually  upwards  of  98  per  cent  sand,  gravel  and  silt);^^  nevertheless 
they  are  grown  very  successfully  on  some  of  the  heavy  soils  of  the  Hawa- 
iian Islands.  It  is  generally  recognized,  however,  that  the  soil  that 
may  be  best  for  a  particular  fruit  or  some  particular  variety  in  one  sec- 
tion may  not  be  best  in  another  section  with  different  chmate  and  distinct 
environmental  conditions.  Thus  in  New  York  the  Concord  grape 
grows  on  a  wide  variety  of  soils  but  seems  to  prefer  a  fairly  strong  loam 
with  considerable  clay;  in  western  Washington  the  same  variety  can 
be  grown  successfully  only  in  hght  sandy  or  sandy  loam  soils  that  tend 
to  hasten  maturity  of  fruit  and  vine.  In  general,  the  more  favorable 
the  texture  of  the  soil  for  both  the  lateral  and  vertical  development  of 
the  root  system,  the  better. 

Requirements  as  to  Depth. — Theoretically,  a  soil  need  be  only  half 
as  rich  as  another  in  order  to  support  equally  well  a  certain  amount 
of  vegetative  growth  if  it  is  of  such  a  character  that  roots  penetrate 
twice  as  deep.  Furthermore,  since  water  is  a  limiting  factor  as  often 
as  plant  nutrients,  a  tree  with  the  deeper  root  system,  though  in  poorer 
soil,  is  really  in  a  better  position  than  one  growing  in  a  richer,  but  shal- 
lower, medium.  Only  under  very  special  conditions  should  ordinary 
deciduous  tree  fruits  be  planted  in  a  soil  in  which  the  roots  cannot  pene- 
trate freely  to  a  depth  of  2}-^  to  3  feet  in  humid  regions  and  to  a  depth  of  5 
to  10  feet  in  arid  and  semi-arid  regions;  soils  that  will  permit  greater  pene- 
tration are  preferable.  Shallowness  of  soil,  hardpan  or  plowsole  close  to 
the  surface,  impervious  subsoil  and  poor  drainage  are  interrelated  factors 
which  check  vegetative  growth,  reduce  yields  and  the  size,  quality  and 
grade  of  the  fruit,  favor  irregular  bearing  and  lead  to  numerous  physio- 
logical troubles,  the  treatment  of  which  is  difficult. 

Classification  of  Soils  According  to  Size  of  Soil  Particles. — Since 
there  is  occasion  repeatedly  to  refer  to  soils  of  different  physical  structure, 
a  classification  based  on  mechanical  analysis,  as  used  by  the  Bureau 
of  Soils  of  the  Federal  Department  of  Agriculture,  is  presented  here^* 
(see  Table  15). 

It  should  be  noted  in  connection  with  this  classification  that  no 
account  is  taken  of  gravel  or  stones  above  2  millimeters  in  diameter. 
Many  soils  contain  rock  particles  larger  than  this  maximum  and  not 
infrequently  these  constitute  a  large  proportion  of  the  soil  volume. 
Accordingly  a  soil  that  in  this  scheme  would  be  classified  as  a  silt  or  even 
a  clay  might  in  fact  be  gravelly  or  rocky  or  stony  in  character.     Though 


ORCHARD  SOILS 


659 


these  larger  components  may  have  a  relatively  unimportant  bearing;  on 
water  holding  capacity,  aeration,  root  penetration  and  related  features, 
they  do  influence  it  materially  in  its  relation  to  tillage  practices  and  they 
often  prove  a  limiting  factor  in  determining  the  kind  of  crop  that  can 
be  grown  in  it  advantageously,  or  the  kind  of  orchard  culture  that  must 
be  practiced.  Thus  of  two  soils  whose  so-called  "fine  earth"  might  ana- 
lyze the  same,  one  might  be  suitable  to  the  strawberry  and  the  other 
quite  unsuited  because  of  the  presence  or  absence  of  large  quantities 
of  rocks  and  coarse  gravel.  It  is  interesting  to  compare  the  mechanical 
analyses  of  several  soils  used  for  fruit  production. 


Table  15.- 


-ScHEME  OF  Soil  Classification,  Based  on  the  Mechanical 
Composition  of  Soils 


(1),  (2) 
2-0.5 
milli- 
meters, 
per  cent. 


(1),  (2),  (3) 

(6) 

2-0.25 

0.05-0.005 

milli- 

milli- 

meters, 

meters, 

per  cent. 

per  cent. 

(7) 
Less  than 
0.005 
milli- 
meters, 
per  cent. 


(6),  (7) 
Less  than 
0.05 
milli- 
meters, 
per  cent. 


Coarse  sand 

Medium  sand .  .  . 

Fine  sand 

Sandy  loam 

Fine  sandy  loam 

Loam 

Silt  loam 

Clay  loam 

Sandy  clay 

Silty  clay 

Clay 


>25 
<25 


>50 
>20 
<20 
>20 
<20 


0-15 

0-15 

0-15 

10-35 

10-35 

<55 

>55 

25-55 

<25 

>55 


0-10 
0-10 
0-10 
5-15 
5-15 

15-25 
<25 

25-35 
>20 

25-35 
>35 


<20 

<20 

<20 

>20<50 

>20<50 

>50 

>60 
<60 

>60 


(1)  "Fine  gravel,"  2-1  millimeters.  (2)  "Coarse  sand,"  1-0.5  millimeters.  (3) 
"Medium  sand,"  0.5-0.25  millimeter.  (6)  "Silt,"  0.05-0.005  millimeter.  (7) 
"Clay,"  less  than  0.005  millimeter.  The  residue  is  composed  of  "fine  sand,"  0.25-0.1 
millimeter  and  "very  fine  sand,"  0.1-0.05  millimeter. 


Mechanical  Analyses  of  Various  Fruit  Soils. — Soils  A  and  C  with  their 
subsoils  B  and  D  (Table  16)  are  fairly  typical  of  the  western  New  York 
fruit  district,  one  of  the  leading  apple  producing  sections  of  the  world. 
Soil  A,  the  Dunkirk  sandy  loam,  contains  64  per  cent,  of  medium  and 
coarse  sand  in  the  surface  and  slightly  more  in  the  subsoil  and  only 
about  5  per  cent,  of  clay  in  both  surface  and  subsoil,  while  soil  C,  the 
Dunkirk  loam,  contains  only  about  30  per  cent,  of  medium  and  coarse 
sand  in  the  surface  soil  and  a  little  more  than  half  that  amount  in  the 
subsoil,  but  approximately  twice  as  much  of  the  finer  materials — clay 


660  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

and  silt.  Here,  indeed,  are  marked  differences  in  the  average  size  of 
soil  particles,  yet  there  are  but  slight  differences  in  the  way  apple  trees 
grow  in  these  soils.  Soil  E,  a  fairly  typical  loess  of  Nebraska,  contains 
no  medium  or  coarse  sand  and  comparatively  large  amounts  of  silt  and 
clay,  yet  it  furnishes  excellent  drainage  and  is  eminently  suited  to  the 
production  of  fruit,  particularly  apples.  Though  probably  the  Billings 
clay  loam  (Soil  M),  with  its  47  per  cent,  clay  and  91  per  cent,  of  clay  and 
silt  combined  is  not  an  ideal  soil  for  apples,  it  is  a  characteristic  soil  of  the 
Grand  Junction  section  of  Colorado  and  where  the  topography  permits 
reasonably  good  drainage,  apple  production  is  profitable.  This  par- 
ticular soil  serves  to  illustrate  the  point  that  the  mechanical  analysis  of  a 
soil  is  not  always  an  accurate  index  to  its  possibilities  for  fruit  growing. 
Though  this  analysis  suggests  very  poor  drainage  and  consequently  a 
lack  of  suitability  for  fruit  crops,  some  of  this  land  is  fairly  well  drained 
and  does  produce  good  fruit  crops.  However,  it  is  but  proper  to  state 
that  the  majority  of  the  Grand  Junction  orchards  are  on  soils  of  a  some- 
what lighter  character.  The  Maricopa  gravelly  sand  of  California  is, 
as  the  name  suggests,  comparatively  light  and  open  in  character,  con- 
taining 57  per  cent,  fine,  medium  and  coarse  sand  and  11  per  cent,  fine 
gravel.  It  is  considered  very  good  for  grapes;  yet  the  Alamo  clay  adobe 
with  95  per  cent,  of  clay  and  fine  silt  is  said  to  be  fairly  suitable  for  grapes 
where  the  topography  is  such  that  drainage  is  not  particularly  poor.^^ 
Probably  the  gray-brown  clay  of  Sonoma,  California,  whose  mechanical 
analysis  is  shown  in  column  0  in  the  table,  represents  more  nearly  average 
soil  conditions  for  the  grape.  Certainly  it  produces  some  of  the  best  wine 
grapes  of  the  country.  ^^  Citrus  fruits  likewise  thrive  on  soils  ranging 
from  heavy  adobes  to  gravelly  loams  and  gravelly  sands.  It  is  interesting 
to  note  the  texture  of  one  of  the  pineapple  soils  of  the  Florida  coast 
(Soil  H  in  the  table) — over  98  per  cent,  fine,  medium  and  coarse  sand. 
The  mechanical  analyses  of  many  other  fruit  soils  which  might  be 
included  would  furnish  little  information,  beyond  that  already  given, 
as  to  the  actual  soil  requirements  of  the  different  fruits.  It  is  evident 
that  the  mechanical  analysis  of  a  soil  carries  some  suggestion  as  to  its 
suitability  for  fruit  crops  of  different  kinds  but  it  is  an  index  only  in  so  far 
as  it  is  an  index  of  texture,  drainage  and  aeration;  these  qualities  depend 
to  a  considerable  extent  on  such  factors  as  topography,  hardpan,  chemi- 
cal composition,  rainfall  and  the  movement  of  underground  water. 
In  other  words,  it  is  hardly  practicable  to  attempt  exact  definition,  in 
terms  of  soil  particle  measurements,  of  the  soil  requirements  for  distinct 
varieties  of  the  same  fruit  or  even  of  different  fruits. 

CONSIDERED    FROM    THE    STANDPOINT    OF    CHEMICAL  COMPOSITION 

The  statement  has  been  made  that,  broadly  speaking,  the  physical 
condition  of  the  soil  is  more  important  in  fruit  production  than  is  its 


ORCHARD  SOILS 


661 


■■»ooj  aoBjmg 
itSiuJojii'BO  'Biaouog 

0 

to  ^ 
d  - 

c 

c 

tc 

CS 

c 

fe: 

11.44 
16.1 
12.3 
28.6 
16.7 
10.9 
4.0 

85OpBJOI00 

^ 

0.1 
0.3 
0.2 
1.7 
6.2 
43.8 
47.4 

95BIUJOJI1BO  'aqopB 

3J3Biq       UmbBOf        UBg 

-^ 

3:42 
1.98 
5.86 
10.40 
50.34 
23.12 

'aqopB     Xbij     ouibiv 

k 

0.3 
0.6 
0.4 
1.1 
3.0 
41.4 
53.5 

99-nnoziJV 
'niBoi  X|[3abj3  udoa!iBj\[ 

■^J 

8.91 
8.50 
9.51 
14.64 
34.45 
16.22 
5.46 

•I'osqng 
Bpuoi^  'I108  oiddBauij 

- 

0.06 
3.08 
57.50 
37.78 

0.20 
0.52 

ES^SBOO 

Bpuou  'tios  ajddBaaij 

a: 

0.23 
3.03 
61.11 
33.76 
0.54 
0.28 
0.50 

^aaj  e  o^  saqoui  i  moi} 
[losqng      jEajiijsdiuBji 

0 

6.7 
19.0 
21.1 
27.6 

6.9 
14.6 

4.9 

•saqaui  i  aoBjjng 

gj-aaiqsduiBH 

Maj«J     'UIBOI     XpuBg 

li. 

3.9 
11.4 
13.1 
16.4 
11.9 
33.4 

9.5 

BqBuie^  '[loeqns  ssao'j 

fel 

0.  10 
25.83 
57.00 

9.49 

•nosqng 

Ci 

0.3 
15.6 
21.5 
27.9 
29.0 

5.5 

•saqoui  6  aoBjang 
(K-^IJOA 
Maj^    'uiBoi    jjaij^una 

0 

4.4 
26.2 

9.7 
30.0 
19.1 
10.6 

•nosqng 
oj'l-JOA  -waN 

'UIBOJ     ApuBS     5IJI5(unQ 

03 

9.0 
60.5 
7.1 
9.7 

8.4 
5.1 

•saqoui  6  aoB;jng 
oj'^-iOA  A^aN 

'tUBOl     ;tpUBS     JJJIJJunQ 

^ 

11.7 
52.3 

3.6 
11.1 
15.5 

5.6 

iScj 

1 

1 

i 

c 

s 
s 

ta 

1 

1 
1 

t 

662  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

chemical  composition.  However,  it  should  not  be  inferred  that  chemical 
composition  is  of  little  significance,  or  that  poor  soils  are  preferable  to 
good  soils  for  orchard  purposes.  On  the  contrary,  the  richer  the  soil 
the  better,  though  productivity  as  it  concerns  the  orchardist,  may  be  quite 
different  from  productivity  as  it  concerns  the  man  growing  cereals  or  fiber 
plants  and  a  soil  that  is  productive  in  pineapple  cultivation  may  be 
unproductive  in  avocado  or  prune  cultivation.  The  only  satisfactory 
measure  of  soil  productivity  is  in  terms  of  crop  production  of  the  specific 
plant  under  consideration.  Hardly  an  orchard  of  commercial  size  any- 
where fails  to  show  differences  in  individual  tree  growth  and  production 
due  apparently  to  variation  in  soil.  However,  thorough  examination 
would  show  that  many  such  differences  are  related  to  variations  in  texture 
or  in  water-holding  capacity  rather  than  in  chemical  composition.  Often 
the  great  inequalities  between  the  size,  longevity  or  productivity  of  trees 
in  various  fruit  producing  sections  may  be  regarded  as  due  largely  to 
chemical  composition.  The  average  differences  between  the  apple 
orchards  of  western  New  York  and  southern  Ohio  is  a  case  in  point — a 
fact  emphasized  by  the  response  of  the  orchards  of  the  latter  section  to 
proper  fertilizer  applications. 

Requirements  of  Different  Crops. — It  should  be  recognized,  too,  that 
certain  fruits  are  particularly  favored  by  the  presence  of  some  element  or 
compound  in  the  soil.  For  instance,  a  high  lime  content  is  said  to  be 
particularly  favorable  for  oil  production  in  the  olive. ^'*  The  cherry  like- 
wise seems  to  respond  favorably  to  lime.  Vitis  berlandieri  flourishes  in, 
even  prefers,  a  limestone  soil;  but  V.  labrusca  is  intolerant  of  lime.^^  The 
chestnut  has  been  shown  to  be  subject  to  chlorosis  on  soils  containing 
upwards  of  3  per  cent,  lime^  and  pears  are  reported  as  frequently 
chlorotic  on  calcareous  soils. ^^  Many  crop  plants  are  known  to  prefer 
a  nearly  neutral  soil  reaction  and  it  has  consequently  been  assumed  that 
most  fruit  plants  do;  some,  however,  as  the  strawberry,  thrive  only  in  an 
acid  medium  and  the  blueberry  demands  a  markedly  acid  soil.^  Certain 
fruits  like  the  grape  are  very  tolerant  toward  "alkali;"  others,  like  the 
mulberry,  are  very  sensitive  to  it.  The  pineapple  is  intolerant  of  man- 
ganese.^^ These  and  the  many  other  peculiarities  of  a  fruit  must  be 
kept  in  mind  and  soils  selected  accordingly  or,  conversely,  the  soil's 
peculiarities  must  be  ascertained  and  the  fruit  species  or  varieties  selected 
accordingly. 

Much  can  be  done  toward  adapting  a  number  of  fruits  to  an  uncon- 
genial soil  by  growing  them  on  a  stock  suited  to  the  soil  in  question. 
This  matter  is  discussed  in  some  detail  in  the  section  on  Propagation. 

Chemical  Analyses  of  Various  Fruit  Soils. — In  the  accompanying 
tables  (17  to  22)  are  presented  chemical  analyses  of  certain  typical  soils 
that  are  more  or  less  noted  for  fruit  production,  together  with  the  analyses 
of  certain  other  soils  that  have  unknown  value  for  fruit  production  or  that 


ORCHARD  SOILS 


663 


are  definitely  known  to  be  unsuitable.  Comparison  may  thus  be  made 
between  "fruit"  soils  and  soils  in  general  and  between  good  and  poor 
fruit  land. 

Table  17. — Chemical  Analyses  of  Average  Soils  of  Humid  and  Arid  Regions 
AND  of  Certain  Orchard  Soils  in  Asia  Minor  and  California 


A,  average  of 
analyses  of  313 

soils  of  arid 

regions,  26  per 

cent 

B,  average  of 
analyses  of  4G6 
soils  of  humid 
regions,''   per 
cent 

C,    soil    from 
Erbelli,    Asia 
Minor  (noted 
for  fig  produc- 
tion),"'per  cent 

D,  Mesa  loam 

from     near 
Riverside,  Cali- 
fornia,'b    per 
cent 

70. 565 
7.266 
0.729 
0.264 
1.362 
1.411 
0.059 
5.752 
7.888 
0.117 
0.041 

1-00 

Fine  earth 

Analysis  of  fine  earth: 

Insoluble  matter 

84  031 

76  33 

63  67 

4.213 
0.216 
0.091 
0.108 
0.225 
0.  133 
3.  131 
4.296 
0.113 
0  0.'i2 

5.35 
1.09 
0.19 
1.96 
1.56 
0.01 
6.49 
3.25 
0.29 
0.06 
1.00 

Potash  (K'>0)    ... 

0  73 

Soda  (NsiiO)    . 

0  36 

Lime  (CaO) 

1.58 

1.85 

Manganese  oxid  (Mn304) 

Ferric  oxid  (FesOs) 

Alumina  (AI2O3) 

Phosphorus  pentoxid  (.  P2O6) 

Sulfur  trioxid    (SO3)   

0.03 
10.02 
5.06 
0.07 
0.01 

Carbonic  acid  (COs) 

1.316                    ....... 

4.945                      3.644 

Water  and  organic  matter 

2.29 

2.74 

Totals   

99.993                  100.178 
0  750                   2  7nn 

99.87                     M  S2 

Humus.  .           

0.27 

0.20 

Nitrogen,  per  cent   in  humus 

Nitrogen,  per  cent    in  soil 

15.870 
0.101 

5.450 
0.122 

Table  18. — Chemical  Analyses  of  Typical  Fruit  Soils  of  Washington^' 


A,  upper 
bench  land, 
Wenatchee, 

per  cent 


Insoluble  silica 

Hydra  ted  silica 

Soluble  silica  (Si02) 

Potash  (K2O) 

Soda  (NazO) 

Lime  (CaO) 

Magnesia  (,MgO) 

Manganese  dioxid  (Mn304).  . 

Iron  oxid  (.FP2O3) 

Alumina  (AI2O3) 

Phosphorus  pentoxide  (PaOs) 

Sulfur  trioxid  (SO3) 

Carbon  dioxid  (CO2) 

Volatile  and  organic  matter.. 

Total 

Humus 

Total  nitrogen  (N) 


81.632 
2.498 
0.316 
0.518 
0.233 
0.714 
0.  186 


4.760 
6.  145 
0.225 


B,  volcanic 

ash,    Walla 

Walla,    per 

cent 


C,    Kenne- 

wick  sand, 

Kennewick, 

per  cent 


77.  772 
5.464 
0.543 
0.328 
0.238 
0.659 
0.104 


4.601 
3.925 
0.037 


84.402 
3.332 
0.265 
0.312 
0.416 
0.944 
0.650 
trace 
4.505 
5.889 
0.  140 
0.018 


D,    sandy  E,    sandy 

soil,  Vashon  soil,  Vashon 

Island,   per  Island,   per 

cent  cent 


76.  652 
8.572 
0.348 
0.126 
0.  106 
0.615 
0.807 


3.064 

4.852 
0.044 


r2 

297 

8 

646 

0 

062 

0 

157 

0 

167 

0 

693 

0.548 

3 

023 

7 

634 

0 

073 

2.969 

5.580 

1.219 

4.467 

6.075 

100. 176 
1.942 
0.061 

99.251 

.1.400 

n.055 

100. 040 
0.465 
0  0.^5 

99. 653 
1.870 
0.077 

100. 275 
3.100 
0.  174 

664  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Table  19. — Chemical.  Analyses  of  Certain  Oregon  Soils*" 


"Redhill" 

land,  Salem, 

per  cent 

White  land, 
Benton 
County, 
per  cent 

Adobe  soil, 
Benton 
County, 
per  cent 

Sandy  loam, 

Wasco 

County, 

per  cent 

"Shot"   land, 

Multnomah 

County, 

per  cent 

Character  of  soil: 

Coarse  material 

28.88 

68.48 
4.38 
0.47 
0.33 
0.40 
0.96 

14.78 

0.63 
10.19 

16.50 
83.50 

70.26 
5.53 
0.06 
0.07 
0.66 

0.04 
13.51 

0.05 
0.03 
10.  13 

2.25 
97.75 

38.91 
16.74 
0.11 
0.03 
1.60 
1.78 
0.08 
23.21 

0.01 
17.44 

25.50 
74.50 

63.65 
12.65 
0.12 
0.16 
1.41 
1.10 

9.23 

0.28 
11.81 

34.00 

Fine  earth 

66.00 

Analysis  of  fine  earths: 

67  40 

Soluble  silica  (SiOz) 

5.18 
0.28 

Soda  (NajO) 

Lime  (CaO) 

0.05 
1.35 

Magnesia  (MgO) 

0.90 

Manganese  (Mn304) 

Iron  (.FejOs) 

0.40 

17.67 

Sulfuric  acid   (SO3) 

Phosphoric  acid  (P2O5) 

Water  and  organic  matter . . 

0.82 
0.34 
7.98 

Total 

99.72 
0.52 

100. 34 
1.22 

100. 00 
1.80 

100.41 
4.42 

100.07 
1.76 

Table  20. — Chemical  Analyses  of  Certain  Florida  Soils 


A,  surface  soil, 
West  Palm 

Beach46  (pine- 
apple land), 
per  cent 

B,     subsoil. 
West  Palm 
Beaches  (pine- 
apple land), 
per  cent 

C,  surface  soil 
Volusia 

County<8 
(orange  land), 

per  cent 

D,  surface  soil, 

muck  land" 

(fruit  and 

truck), 

per  cent 

Silica  (Si02)  insoluble 

99.  3070 
0.0147 
0.0037 
0.0000 
0.0048 
0.2210 
0.0100 
0.0038 
0.4860 
0. 2000 
0.0100 

99.  5840 
0.0197 
0.0000 
0.0000 
0.0126 
0.  2400 
0.0087 
0.0038 
0.1620 
0.0675 
0.0045 



96.0852 

0.0526 
0.0145 
0.0208 
1.1726 
0.1600 
0.0096 

0.0890 

trace 

2.3910 

53.  5900 

Silica  (Si02;  soluble 

Magnesia  (MgO) 

trace 

Potash  (.K2O) 

0.  1500 

Iron  and  alumina  (Fe203  and  AI2O3). 
Phosphorus  pentoxid  (PzOs) 

10.0100 
trace 
0. 0500 

Volatile  matter 

Nitrogen  (N) 

1.500 

Chlorin     

0.0200 

34.9700 

ORCHARD  SOILS  665 

Table  21. — Chemical  Analyses  of  Manganiferous  and  Normal  Soils  of  Oahu^^ 


Constituents 

Manganiferous  soil 

Normal  soil 

Soil 

Subsoil 

Soil 

Subsoil 

33.46 
0.83 
0.40 
1.39 
0.5.5 
9.74 

19.65 

15.50 
0.21 
0.16 
0.73 

19.93 

36.06 
0.74 
0.42 
0.86 
0.43 
8.76 

21.51 

15.74 
0.16 
0.09 
1.09 

14.45 

40.89 
0.51 
0.21 
0.51 
0.37 
0.22 

35.72 
3.58 
0.07 
0.09 
3.83 

14.22 

39.25 

Potash  (K2O) 

0  60 

Soda  (Na20) 

0  32 

Lime  (CaO) 

0  66 

0  38 

0  06 

Ferric  oxid  (Fe203) 

Alumina  (AlaOs^ 

33.28 
8.66 

Phosphorus  pentoxid  (PzOb) 

Sulfur  trioxid  (SO3) 

0.08 
0  07 

Titanic  oxid  (TiOa) 

2  74 

Loss  on  ignition 

13.99 

Total 

Nitrogen  (N) 

100.35 
0.39 

100.31 
0.23 

100.22 
0.34 

100.09 
0  25 

Table  22. — Chemical  Analyses  op  Miscellaneous  Soils 


.4,  Maricopa 

gravelly  loam 

Arizona,'" 

per  cent 

B,  Peach  belt 
soil,    South 

Haven, 

Mich. ,35  per 

cent 

C,  Olive  or- 
chard  soil, 

Ventura, 

Cal.,s  per 

cent 

D,  Slate  col- 
ored upland 
adobe  Ala- 
meda. Cal..« 
per  cent 

E,  Loess  soil, 

Kansas  City, 

Mo. ,30  per 

cent 

Insoluble  silica  (SiOi) 

Soluble  silica  (Si02) 

72.  35 
10.29 
2.07 
1.36 
0.66 
0.28 
4.41 
4.94 
0.09 
0.03 
0.87 
0.03 

0.51 
0.04 

87.23 

0.51 
0.46 
0.83 
0.34 
1.52 
2.87 
0.  13 
0.20 

5.64 
0.07 

82.11 
6.88 
0.67 
0.57 
0.47 
0.42 
5.26 
1.30 
0.21 
0.09 

2.23 
0.78 
0.074 

64.790 
16.564 
0.868 
0.978 
0.579 
0.  100 
3.791 
7.718 
0.143 
0.006 

4.601 
0.697 

34.98 

Lime  (CaO) 

1   70 

Magnesia  (MgO) 

1    12 

Potash  (KzO) 

1   84 

Soda  (Na20) 

1   06 

Phosphoru^  pentoxid  (PaOs).  . 
Sulfur  trioxid  (SO3) 

0.09 
0.02 

Chlorine 

Water  and  organic  matter .... 
Humus 

Nitrogen  (N) 

666  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Probably  the  most  striking  fact  brought  out  in  a  study  of  the  chemical 
analyses  of  fruit  soils  (Tables  17  to  22)  is  their  extreme  variability  and 
their  frequent  wide  divergence  from  the  averages  of  the  soils  of  either  the 
humid  or  arid  sections.  It  is  impossible  to  associate  certain  extreme  soil 
types  with  special  crops.  For  instance  a  single  fruit  crop  would  hardly 
be  expected  to  do  equally  well  on  soil  like  that  shown  in  columns  A 
and  B  of  Table  20  and  those  shown  in  Table  21.  The  Oahu  soils  con- 
tain seven  to  20  times  as  much  phosphorus,  50  to  80  times  as  much  potash 
and  30  to  40  times  as  much  nitrogen  as  those  of  the  Florida  coast;  the 
difference  in  some  of  the  other  constituents  is  as  great  or  greater.  Yet 
these  soils  are  almost  equally  well  suited  to  the  pineapple,  though  their 
fertilizer  requirements  are  somewhat  different.  The  two  Hawaiian  soils 
shown  in  Table  21  resemble  each  other  closely,  much  more  closely  than 
they  resemble  the  Florida  soil,  but  they  show  a  marked  disparity  in  their 
suitability  for  fruit  culture  and  the  soil  that  is  the  richer  in  the  nutrient 
elements,  nitrogen,  potash  and  phosphoric  acid,  is  the  poorer  when  meas- 
ured in  terms  of  pineapple  production.  Though  the  first  three  soils  from 
Washington  whose  analyses  are  given  in  Table  18  show  marked  differ- 
ences in  composition,  especially  in  their  phosphorus  and  nitrogen 
content,  all  are  noted  for  their  fruit  production  and  proof  that  even  a  single 
fruit,  as  the  apple,  reaches  a  higher  stage  of  perfection  in  one  than  in 
the  others  is  difficult.  The  soil  designated  in  Table  19  as  "White  land" 
does  not  differ  greatly  in  its  analysis  from  the  "Redhill"  or  the  "Shot" 
land,  except  that  it  contains  less  potash  and  phosphoric  acid.  These  ele- 
ments are  present,  however,  in  larger  amounts  than  in  some  of  the  other 
fruit  soils  whose  analyses  are  given.  Yet  this  "White  Land"  is  not 
suited  to  fruit  production  and  the  "Redhill"  land  and  the  "Shot"  land 
are  among  the  best  fruit  soils  of  the  state.  The  factor  determining  the 
difference  betwen  them  is  drainage.  The  analyses  shown  in  columns  D 
and  E  of  Table  18  are  particularly  interesting  in  that  both  soils  are  from 
near  by  fields  on  Vashon  Island,  Washington.  The  differences  in  compo- 
sition as  shown  by  the  analyses  are  comparatively  small;  both  are  con- 
sidered well  suited  to  strawberry  culture  and  the  average  variety  does 
well  upon  both  soils.  Yet  the  Clark  variety  is  reported  as  thriving  only 
on  the  one  and  as  failing  to  produce  satisfactorily  on  the  other.^^ 

Evidently  the  relation  of  the  chemical  composition  of  the  soil  to 
suitability  for  fruit  growing  is  far  from  well  understood,  much  less 
established.  Without  doubt  different  fruits  and  possibly  distinct  varie- 
ties of  the  same  fruit  require,  or  at  least  grow  better  in,  soils  of  somewhat 
dissimilar  chemical  composition.  However,  since  present  methods  of 
analysis  do  not  differentiate  clearly  between  those  requirements  they  do 
not  actually  measure  soil  productivity  as  it  is  expressed  in  terms  of  fruit 
production  and  they  do  not  afford  a  very  accurate  index  to  fruit  crop 
adaptation. 


ORCHARD  SOILS 


667 


Evidence  on  Soil  Requirements  from  Fertilizer  Ex-periments. — Point 
is  lent  the  last  statement  by  data  presented  in  Table  23  assembled 
by  Stewart,  showing  the  response  to  fertilizer  applications  of  trees  growing 
in  soils  of  varying  productivity.  In  commenting  on  these  data  Stewart^^ 
remarks:  "These  figures  show  that  the  correlation  between  soil  composi- 
tion, as  determined  by  the  methods  of  soil  sampling  and  analysis  above 
specified,  and  the  actual  response  of  the  associated  trees  to  additional 
fertilization  is  either  exceedingly  slight  or  absent  entirely.  One  would 
naturally  expect  that  the  largest  response  would  appear  where  the  chem- 
ical fertility  of  the  soil  was  lowest,  and  vice  versa.  This  evidently  has  not 
occurred.     In  fact,  the  least  response  to  practically  all  types  of  fertiliza- 


Table  23. — Relation  of  Soil  Composition  to 

{After  SteivarP^) 

Fertii 

IZER 

Response 

Soil  type 

Nitro- 
gen 

Phosphorus  (P2O5) 

Potash    (K2O) 

Response  to  fertili- 
zation.      (Per  cent   in- 
crease   in    yield) 

Per  cent, 
(total) 

Per  cent, 
(total) 

Per  cent, 
(avail- 
able) 

Per  cent, 
(total) 

Per  cent, 
(avail- 
able) 

N 

p 

K 

CF> 

M2 

Porters 

0.132 
0.071 
0.  118 
0.158 
0.163 
0.300 

0.244, 
0.183 
0.  123 

0.093 
0.029 
0.087 
0.116 
0.132 
0.233 

0.161 
0.315 
0.  135 

0.017 
0.009 
0.002 
0.012 
0.007 
0.043 

0.032 
0.122 
0.006 

2.35 
0.66 
1.81 
2.23 
1.69 
1.78 

1.27 
1 .  55 
1.97 

0.020 
0.010 
0.029 
0.040 
0.045 
0.051 

0.026 
0.  145 
0.042 

24 

3 
148 
15 
94 
27 
CF3 
16 
24 

9 

1 
5 

27 

.1 

3 

M3 

21 
26 
9 

33 
1 

23 
3 
9 

69 

43 
29 

181 
24 
93 

144 

75 
26 
92 

20 

Montalto 

30 

DoKalb 

294 

Chester 

46 

117 

Lackawanna 

Frankstown 

200 

86 
24 

Hagerstown 

83 

1  Complete  fertilizer.     2  Manure.     ^  pgr  cent,  increase  in  growth,  instead  of  yield. 

tion  has  occurred  in  the  soil  analyzing  poorest  of  all,  and  some  of  the  largest 
responses  have  appeared  in  the  chemically  richest  soils.  The  ordinary 
methods  of  soil  analysis  are  not  yet  adequate  to  furnish  a  reliable  indi- 
cation of  the  fertility  needs  of  an  orchard.  Trees  on  chemically  rich 
soils  will  not  of  necessity  prove  unresponsive  to  additional  fertilization, 
nor  will  trees  on  chemically  poor  soils  always  prove  responsive.  In  other 
words,  some  other  indicator  than  the  chemical  composition  of  the  soil, 
as  here  determined,  must  be  relied  upon  to  determine  the  real  need  of 
additional  fertility  in  an  orchard.  At  present,  therefore,  the  surest  and 
most  delicate  test  yet  devised  for  determining  the  fertility  needs  of  an 
orchard  soil  is  the  actual  response  of  the  living  tree  in  the  soil  concerned 
to  appropriate  fertility  additions." 

The  soil  is  a  very  complex  substance  and  the  soil  solution  likewise; 
apparently  absolute  amounts  of  certain  elements  or  compounds  that  it 
contains  are  not  so  important  as  the  state  of  balance  or  equilibrium 


668  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

existing  between  them.  No  better  evidence  to  this  effect  is  needed  than 
some  of  the  facts  brought  out  by  the  analyses  of  the  Florida  and  Hawaiian 
pineapple  soils  that  have  been  mentioned.  Certainly  it  would  not  be 
suspected  from  these  analyses  that  in  the  Hawaiian  soils  with  their  20  to 
35  per  cent,  of  iron  (indeed  there  is  one  local  pineapple  district  in  the 
Hawaiian  Islands  where  the  soil  contains  85  per  cent,  iron  and  titanium ^^) 
the  plants  often  show  symptoms  of  iron  starvation  and  that  iron  sulphate 
is  their  most  valuable  fertilizer,  though  less  than  three-tenths  of  1  percent, 
of  iron  furnishes  an  ample  supply  in  the  Florida  sands.  The  relationship 
between  soil  and  crop  is  more  than  that  existing  between  the  different 
factors  in  a  problem  in  addition  and  subtraction.  Other  aspects  of  this 
general  question  are  discussed  in  the  sections  on  Water  Relations  and 
Nutrition. 

VEGETATION  AS  AN  INDEX  TO  CROP  ADAPTATION 

Though  at  present  no  single  feature  of  the  chemical  or  mechanical 
composition  of  the  soil  can  be  designated  the  chief  cause  for  the  way 
some  fruit  crops  grow  on  it,  soil  differences,  even  slight  differences,  may 
be  of  great  significance  to  the  fruit  grower.  His  study  of  soils  should 
include  more  than  the  features  brought  into  contrast  by  chemical  and 
mechanical  analyses.  The  types  of  the  native  vegetation  may  serve  as 
very  useful  indices  of  probable  productivity  when  planted  to  cultivated 
crop  plants  belonging  to  the  same  or  a  closely  related  genus  or  family; 
knowledge  of  plant  ecology  may  make  it  possible  to  predict  with  accuracy 
the  way  some  entirely  unrelated  plant  will  behave  on  the  soil  in  question. 
For  instance,  in  Ohio,  land  upon  which  the  sugar  maple,  beech,  oak,  or 
chestnut  thrive  naturally  is  hkely  to  be  well  suited  to  the  apple,  but  land  on 
which  the  elm  is  native  is  seldom  desirable  for  that  fruit. ^^  In  western 
Oregon  and  western  Washington,  hill  land  supporting  a  vigorous  growth 
of  the  native  "brake"  or  fern  (Pteridium  aquilinuvi  pubescens)  is  charac- 
teristically good  for  prunes.  In  the  Ozarks  "post-oak"  land  is  good  for 
grape  culture.  Ney^^  has  pointed  out  that  the  kinds  of  forest  trees  grow- 
ing on  land  often  form  something  of  an  index  of  its  chemical  condition. 
He  says,  "As  regards  the  chemical  composition  of  the  soil,  even  slightly 
sour  marshy  soils  are  unfavorable  to  all  species  of  trees  except  alder, 
birch,  and  spruce ;  whilst  sour  soils,  liable  to  dry  up  at  certain  seasons, 
are  unsuited  to  all  except  birch,  spruce,  Scots  and  Weymouth  pines." 
Ash,  maple,  sycamore,  and  elm  require  a  moderate  quantity  of  lime  and 
beech,  hornbeam,  oak,  as  also  larch  and  Austrian  pine,  thrive  best  on  soils 
that  have  at  least  some  lime  in  their  composition.  The  hardwoods— oak, 
ash,  maple,  sycamore,  elm,  chestnut,  beech  and  hornbeam — also  appear 
to  demand  the  presence  of  a  considerable  quantity  of  potash,  while  on  the 
other  hand,  spruce,  silver  fir  and  especially  Scotch  pine  and  birch  thrive 


ORCHARD  SOILS  669 

on  soils  rich  neither  in  lime  nor  potash.  In  Florida  a  dense  growth  of 
palmettos  is  Hkely  to  indicate  an  undesirable  hardpan  or  subsoil;  such 
soils  should  be  avoided  in  citrus  fruit  plantings. 

Not  only  are  the  kinds  of  native  trees  or  plants  useful  in  determining 
the  value  of  a  soil  for  fruit  growing,  but  the  type  of  growth  that  these 
species  make  is  of  equal  significance.  Thus  Vosbury"  states,  "Most  of 
the  recent  citrus  plantings  in  Florida  have  been  made  on  high  pinelands. 
Three  grades  of  high  pineland  are  recognized.  The  best  grade  is  charac- 
terized by  large  straight-growing  pines  with  occasional  oaks,  hickories, 
or  other  hardwood  trees.  The  soil  is  a  sandy  loam,  fairly  rich  in  humus, 
and  is  underlaid  with  a  clay  subsoil  at  a  depth  of  6  feet  or  less.  In 
second-grade  pinelands  the  pine  trees  are  smaller  and  there  are  few  or  no 
hardwoods,  while  the  subsoil  is  further  from  the  surface.  In  the  third 
or  poorer  grade  the  pines  are  still  smaller  and  scrubbier  and  the  clay 
subsoil  far  below  the  surface  soil." 

The  soils  picked  as  especially  suited  to  certain  field  crops  in  some 
sections  are  less  likely  to  furnish  a  reliable  guide  to  their  suitability  to 
certain  fruits.  In  New  England  apples  will  generally  do  well  in  those 
soils  considered  best  suited  to  corn,  for  only  the  lighter  earlier  soils  are 
able  properly  to  mature  that  crop  in  that  section,  but  in  Illinois  the  best 
corn  land  is  quite  different  in  character  and  the  best  apple  land  is  outside 
the  corn  belt. 


ADAPTATION  OF  VARIETIES  TO  PARTICULAR  SOILS 

In  addition  to  the  more  or  less  general  soil  requirements  for  different 
kinds  of  fruits  that  have  been  mentioned,  particular  varieties  or  groups 
exhibit  certain  soil  preferences. 

For  instance,  in  speaking  of  soil  adaptations  of  plums,  Hedrick^^ 
states  that  the  Domesticas  and  Insititias  grow  most  satisfactorily  on  rich 
clay  loams,  while  the  Trifloras,  Hortulanas  and  Munsonianas  give  best 
results  on  light  soils.  These  group  names,  however,  represent  distinct 
species  and  consequently  differences  greater  than  those  usual  between 
varieties  of  the  same  kind  of  fruit. 

Wilder,^^  who  has  made  a  special  study  of  the  fruit  soils  of  southern  New 
England,  makes  the  following  statements  regarding  the  special  soil  requirements 
of  certain  well  known  apple  varieties:  "Soils  grading  from  medium  to  semi-light 
fulfill  the  best  requirements  of  the  Baldwin.  This  grouping  would  include  the 
medium  to  light  loams,  the  heavy  sandy  loams,  and  also  the  medium  sandy  loams, 
provided  they  were  underlaid  by  soil  material  not  lighter  than  a  medium  loam 
nor  heavier  than  a  Ught  or  medium  clay  loam  of  friable  structure."  From  this 
broad  generalization  it  will  be  seen  that  the  surface  soil  should  contain  an  ap- 
preciable amount  of  sand.     The  sands,  moreover,  should  not  be  all  of  one  grade, 


670  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

that  is,  a  high  percentage  of  coarse  sand  would  give  a  poor  soil,  whereas  a  moderate 
admixture  of  it  with  the  finer  grades  of  sand,  together  with  sufficient  clay  and 
silt,  would  work  no  harm. 

"A  surface  soil  of  heavy,  silty  loam  or  light,  silty,  clay  loam  underlain  by 
silty  clay  loam  excells  for  the  'green'  Rhode  Island  Greening.  Such  soil  will 
retain  sufficient  moisture  to  be  classed  as  a  moist  soil,  yet  it  is  not  so  heavy  as 
ever  to  be  ill  drained  if  surface  drainage  is  inadequate.  The  soil  should  be 
moderately  rich  in  organic  matter,  decidedly  more  so  than  for  the  Baldwin. 
Such  soil  conditions  maintain  a  long  seasonal  growth  under  uniform  conditions 
of  moisture,  and  thus  produce  the  firm  yet  crisp  texture,  the  remarkable  juiciness 
and  the  high  flavor  for  which  this  variety  is  noted  when  at  its  best.  If  grown  on 
a  soil  too  sandy,  the  Rhode  Island  Greening  lacks  fineness  of  grain,  flavor  and  the 
juicy  quahty  in  greater  or  lesser  degree,  depending  on  the  extent  of  the  departure 
from  those  soil  characteristics  which  contribute  to  its  production. 

"This  variety  [Northern  Spy]  is  one  of  the  most  exacting  in  soil  requirements. 
To  obtain  good  quality  of  fruit,  i.e.,  fine  texture  juiciness  and  high  flavor,  the 
soil  must  be  moderately  heavy,  and  for  the  first  two  qualities  alone  the  Rhode 
Island  Greening  soil  would  be  admirable.  The  fact  that  the  Northern  Spy  is  a 
red  apple,  however,  makes  it  imperative  that  the  color  be  well  developed  and  the 
skin  free  from  the  greasy  tendency.  This  necessitates  a  fine  adjustment  of  soil 
conditions,  for  the  heaviest  of  the  soils  adapted  to  the  Rhode  Island  Greening 
produces  Northern.  Spies  with  greasy  skins  and  usually  of  inferior  color.  Its 
tendency  to  grow  upright  seems  to  be  accentuated  by  too  clayey  soils,  if  well 
enriched  and  such  soils  tend  to  promote  growth  faster  than  the  tree  is  able  to 
mature  well.  On  the  other  hand,  sandy  soils,  while  producing  good  color  and 
clear  skins,  fail  to  bring  fruit  satisfactory  in  quality  with  respect  to  texture  and 
flavor.  The  keeping  quality,  too,  is  inferior  to  that  of  the  Spy  grown  on  heavier 
soils  in  the  same  district.  Hence  the  soil  requirements  of  this  variety  are  de- 
cidedly exacting,  and  are  best  supplied  apparently  by  a  medium  loam  underlain 
by  a  heavy  loam  or  light  clay  loam.  It  should  not  be  planted  on  a  soil  lighter 
than  a  very  heavy,  fine,  sandy,  loam,  underlain  by  a  light  clay  loam,  or  possibly  a 
heavy  loam.  On  light  soils  the  Nothern  Spy  very  often  yields  less  per  acre 
than  the  Baldwin. 

''Both  Ben  Davis  and  Gano  show  less  effect  from  variation  in  the  soils  upon 
which  they  are  grown  than  any  others  observed." 

In  speaking  of  tlie  special  soil  requirements  of  peach  varieties  the  same  author 
has  this  to  say: 

"Judging  from  the  experience  of  a  very  large  number  of  growers  in  Connecti- 
cut and  in  other  States,  combined  with  field  observations,  it  seems  evident  that 
the  Champion  peach  is  especially  sensitive  to  any  condition  of  subsoil  which 
hinders  the  ready  movement  of  moisture  within  a  probable  depth  of  as  much  as 
4  feet  from  the  surface.  Carman  and  Mountain  Rose  are  not  quite  so  dependent 
as  the  Champion  on  soils  that  drain  out  hastilj^,  and  while  they  succeed  best  on 
soils  of  a  little  greater  moisture-holding  capacity  than  the  Champion,  they  never- 
theless give  the  best  results  on  deep  and  well-drained  soils.  The  Elberta  and 
the  Belle  thrive  on  well-drained  soils  that  are  somewhat  stronger  than  the  varie- 
ties previously  mentioned. "^^ 


ORCHARD  SOILS  671 

There  Is  some  reason  to  believe  that  the  importance  of  these  variety 
preferences  is  often  overemphasized.  For  instance  to  assert  that  the 
Yellow  Newtown  (Albemarle  Pippin)  apple  will  do  well  only  on  the  so- 
called  "pippin"  soils  of  Virginia  and  North  Carolina  is  to  misstate  the 
facts,  except  perhaps  for  the  soils  of  those  particular  states.  The  variety 
does  equally  well  on  quite  different  soils  in  the  Hudson  River,  Hood 
River  and  Rogue  River  valleys  and  in  New  South  Wales,  though  on  these 
other  soils  it  may  develop  a  slightly  different  but  in  no  way  inferior, 
shape,  color  or  flavor.  Some  of  the  variation  in  the  chemical  composition 
of  fruits  is  without  doubt  due  to  diversities  in  soil  and  in  some  parts  of 
the  world  these  differences  are  regarded  as  of  considerable  importance 
in  the  production  of  grapes  for  wine;  however,  much  of  the  variation  in 
composition  is  due  to  other  factors  of  environment,  such  as  temperature, 
sunlight  and  humidity.  Their  influence  must  be  subtracted  before  it 
can  be  said  that  the  difference  in  the  quality  of  fruit  from  two  different 
sections,  or  even  orchards,  is  due  to  soil  variation.  Nevertheless,  the 
ways  in  which  soil  influences  the  development  of  individual  varieties  may 
well  be  studied,  for  often  the  information  gained  can  be  of  much  use  in 
actual  fruit  production.  For  instance,  if  a  piece  of  land  that  is  to  be 
planted  to  apple  trees  includes  some  light  and  some  heavy  soil  and  two 
varieties,  one  a  red  and  the  other  a  yellow  apple,  are  to  be  set,  it  will 
generally  be  wise  to  plant  the  red  variety  on  the  lighter  soil  and  the 
yellow  variety  on  the  heavier,  so  far  as  possible.  Though  soil  probably 
exerts  very  little,  if  any,  direct  influence  on  pigment  production 
in  the  fruit,  the  type  of  vegetative  growth  obtained  on  the  lighter  soil 
is  likely  to  permit  and  encourage  higher  coloration  of  the  fruit  than  that 
obtained  on  the  finer  textured  land. 

It  is  easier  to  modify  through  treatment  the  chemical  condition  of  the 
soil  than  its  physical  condition  and  obviouslj^,  it  is  generally  easier  to 
modify  surface  soil  than  subsoil.  The  subsoil  must  be  taken  largely  as 
it  is  found.  Consequently  in  selecting  a  piece  of  land  for  fruit  growing 
the  subsoil  should  be  given  specially  careful  consideration,  particularly 
as  regards  its  physical  condition.  Both  physical  and  chemical  condition 
of  the  surface  soil  may  be  modified  materially,  but  to  effect  any  consider- 
able change,  particularly  in  physical  character,  is  expensive.  The  grower 
should  never  forget  that  the  business  must  yield  a  fair  return  on  the 
investment. 

Summary. — In  general  fruit  crops  demand  the  same  qualities  in  a 
soil  as  cereal  or  forage  plants.  On  account  of  their  growing  habits, 
however,  depth  of  soil,  character  of  subsoil  and  general  physical  condition 
are  of  relatively  greater  importance  to  the  former.  Different  fruit  crops 
show  varying  adaptation  to  soils  of  quite  dissimilar  textures.  Practically 
all,  however,  are  alike  in  requiring  considerable  depth,  thorough  aeration 
and  freedom  from  hardpan,  plowsole  or  other  impervious  strata.     It  is 


672  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

impracticable  at  present  to  attempt  a  definition  of  the  soil  requirements 
of  different  fruit  plants  in  terms  of  mechanical  analysis. 

Soils  that  are  unproductive  from  the  standpoint  of  cereal  crops  are 
often  productive  from  the  standpoint  of  fruit  production  and  the  reverse 
situation  often  occurs.  It  is  even  more  impracticable  to  attempt  a  defini- 
tion of  the  soil  requirements  of  different  fruits  in  terms  of  chemical  compo- 
sition, than  in  terms  of  mechanical  analysis.  The  character  of  the  vegeta- 
tion growing  naturally  on  a  soil  furnishes  one  of  the  best  indices  to  the 
kinds  of  fruit  that  may  be  expected  to  thrive  on  it.  Though  there  are 
indications  of  marked  adaptation  of  particular  varieties  to  certain  soil 
types,  the  importance  of  such  special  adaptations  is  often  exaggerated. 

Suggested  Collateral  Readings 

Batchelor,  L.  D.,  and  West,  F.  L.     Variation  in  Minimum  Temperatures  Due  to  the 

Topography  of  a  Mountain  Valley  in  its  Relation  to  Fruit  Growing.     Utah  Agr. 

Exp.  Sta.  Bui.  141.     1915. 
Wickson,  E.  J.     California  Fruits:  How  to  Grow  Them.     Pp.  27-37.     San  Francisco, 

1910. 
Russell,  E.  J.     Soil  Conditions  and  Plant  Growth.     Chapters  3  and  8.     Pp.  52-79; 

153-169.     London,  1915. 
Bowman,  I.     Forest  Physiography.     Pp.  27-40,  107-126.     New  York,   1914. 

Literature  Cited 

1.  Abbe,  C.     U.  S.  D.  A.,  Mo.  Weather  Rev.  21.     1893.     Cited  by  Garriot,  E.  B 

U.  S.  D.  A.  Farmers'  Bui.  104.     1899. 

2.  Batchelor,  L.  D.,  and  West,  F.  L.     Utah  Agr.  Exp.  Sta.  Bui.  141.     1915. 

3.  Bigelow,  F.  H.     U.  S.  D.  A.,  Weather  Bur.  Bui.  R.     1908. 

4.  Cal.  Agr.  Exp.  Sta.  Bui.  25.     1884. 

5.  Cal.  Agr.  Exp.  Sta.  Rept.  for  1894-95.     P.  15.     1896. 

6.  Cal.  Agr.  Exp.  Sta.  Ann.  Rept.     1903-1904. 

7.  Coville,  F.  V.     U.  S.  D.  A.,  Bur.  PL  Ind.  Bui.  193.     1910. 

8.  Finch,  C,  and  Baker,  D.  O.     Geography  of  the  World's  Agriculture.     U.  S.  D.  A., 

Office  Farm  Management.     1917. 

9.  Fliche,  P.,  and  Grandeau,  L.     Ann.  Chem.  et  Phys.  ser.  5.     2:  354-379.     1874. 

10.  Forbes,  R.  H.     Ariz.  Agr.  Exp.  Sta.  Bui.  28.     1897. 

11.  Fritz,  H.     Intern,  wissensch.   Bibliothek,   Band  68.     Leipzig^   1889.     Cited  by 

Abbe,  C.     U.  S.  D.  A.,  Weather  Bur.  Bui.  36.     1905. 

12.  Gager,  C.  S.     J.  N.  Y.  Bot.    Garden   8.     1909.     Cited   in    U.    S.    D.  A.,  Mo. 

Weather  Rev.     36:  63.     1908. 

13.  Georgeson,  C.  C.     Alaska  Agr.  Exp.  Sta.  Ann.  Rept.     P.  9.     1906. 

14.  Ibid.     P.  21.     1907. 

15.  Ibid.     P.  20.     1908. 

16.  Ibid.     Pp.  8,  9.     1909. 

17.  Green,  W.  J.     Ohio  Agr.  Exp.  Sta.  Bui.  137.     1903. 

18.  Hann,  J.     Handbuch  der  Klimatologie.     Stuttgart,  1911. 

19.  Hedrick,  U.  P.     Grapes  of  New  York.     Pp.  131,  152.     Albany,  1908. 

20.  Hedrick,  U.  P.     N.  Y.  Agr.  Exp.  Sta.  Bui.  314.     1909. 

21.  Hedrick,  U.  P.     Plums  of  New  York.     P.  113.     Albany,  1911. 

22.  Heyer,  G.     Forstl.  Bodenk.  u.  Klimatol.     P.  488.     1856.     Cited  in  Nisbet,  J. 

Studies  in  Forestry.     P.  53.     Oxford,  1894. 


GEOGRAPHIC  INFLUENCES  673 

23.  Higgins,  J.  E.     Hawaii  Agr.  Exp.  Sta.  Bui.  7.     1904. 

24.  Higgins,  J.  E.,  and  Holt,  V.  S.     Hawaii  Agr.  Exp.  Sta.  Bui.  32.     1914. 

25.  Hilgard,  E.  W.     Cal.  Agr.  Exp.  Sta.  Kept,  for  1890.     P.  41.     1891. 

26.  Hilgard,  E.  W.     Cal.  Agr.  Exp.  Sta.  Rept.  for  1892-3.     P.  328.     1894. 

27.  Hilgard,  E.  W.     Cal.  Agr.  Exp.  Sta.  Rept.  for  1897-1898.     P.  41. 

28.  Hilgard,  E.  W.     Soils,  6th  ed.     P.  182.     1914. 

29.  Hodgson,  R.  W.     Cal.  Agr.  Exp.  Sta.  Bui.  276.     1917. 

30.  Hopkins,    C.    G.     Soil    Fertility    and    Permanent    Agriculture.     P.    69.     1910. 

(Computed  from  his  data.) 

31.  Husmann,  G.  C.     U.  S.  D.  A.,  Bur.  PL  Ind.  Bui.  172.     1910. 

32.  Jaffa,  M.  E.     Cal.  Agr.  Exp.  Sta.  Rept.  for  1892-3.     P.  238.     1894. 

33.  Johnson,  M.  O.     Hawaii  Agr.  Exp.  Sta.  Press  Bui.  51.     1916. 

34.  Kearney,  T.  H.     U.  S.  D.  A.     Bur.  PI.  Ind.  Bui.  125.     1908. 

35.  Kedzie,  R.  C.     Mich.  Agr.  Exp.  Sta.  Bui.  99.     1893. 

36.  Kelley,  W.  P.     Hawaii  Agr.  Exp.  Sta.  Bui.  26.     1912. 

37.  Kerner,  A.,  and  Oliver,  F.  W.     Natural  History  of  Plants.     1  (2):  528.     New 

York,  1895. 

38.  King,  F.  A.     Wis.  Agr.  Exp.  Sta.  Ann.  Rept.  12:  268-272.     1895. 

39.  Kinman,  C.  F.     Porto  Rico  Agr.  Exp.  Sta.  Bui.  24.     1918. 

40.  Lippincott,  J.  S.     U.  S.  Rept.  Com.  Agr.     Pp.  137-190.     1866. 

41.  Loughridge,  R.  H.     Cal.  Agr.  Exp.  Sta.  Bui.  133.     1901. 

42.  Mac  Dougal,  D.  T.     Mem.  Hort.  Soc.  N.  Y.     2:  3-22.     1907. 

43.  Mason,  S.  C.     U.  S.  D.  A.     Bui.  271.     1915. 

44.  Mass.  St.  Board  of  Agr.,  Ann.  Rept.     59:  14-15.     1911. 

45.  Merriam,  C.  H.     U.  S.  D.  A.,  Div.  of  Biol.  Surv.  Bui.  10.     1898. 

46.  Miller,  H.  K.,  and  Hume,  H.  H.     Fla.  Agr.  Exp.  Sta.  Bui.  68.     1903. 

47.  Ney.     Lehre  von    Waldbau.     P.    64.     1885.     Cited   in    Nisbet,    J.     Studies   in 

Forestry.     Oxford,  1894. 

48.  Persons,  A.  A.     Fla.  Agr.  Exp.  Sta.  Bui.  43.     1897. 

49.  Riviere,  G.,  and  Bailhache,  G.     Prog.  Agr.  et  Vit.     53  (15):  453-454.     1910. 

50.  Shaw,  G.  W.     Ore.  Agr.  Exp.  Sta.  Bui.  50.     1898. 

51.  Shreve,  F.     Carn.  Inst.  Wash.  Pub.  217.     1915. 

52.  Stewart,  J.  P.     Pa.  Agr.  Exp.  Sta.  Bui.  153.     1918. 

53.  Thatcher,  R.  W.     Wash.  Agr.  Exp.  Sta.  Bui.  85.     1908. 

54.  U.  S.  D.  A.,  Bur.  Soils,  Bui.  5.     1896. 

55.  U.  S.  D.  A.,  Operations  Div.  Soils  for  1900.     P.  303.     1901. 

56.  Ibid,  for  1901.     P.  464.     1902. 

57.  Ibid,  for  1904.     P.  1127.     1905. 

58.  Ibid,  for  1905.     P.  959.     1907. 

59.  Ibid,  for  1909.     P.  1721.     1921. 

60.  Vinson,  R.  S.,  and  Russell,  E.  J.     J.  Agr.  Sci.     2:  225.     1907. 

61.  Vosbury,  E.  D.     U.  S.  D.  A.  Farmers'  Bui.  1122.     1920. 

62.  Wheeler,  H.  J.     U.  S.  D.  A.  Farmers'  Bui.  77.     1905. 

63.  'UTiitney,  M.     U.  S.  D.  A.,  Bur.  Soils.  Bui.  13.     1898. 

64.  Wilcox,  E.  V.     Tropical  Agriculture.     Pp.  2,  5.     1916. 

65.  Ibid.     P.  19.     1916. 

66.  Wilder,  H.  J.,     Mass.  St.  Board  Agr.  Ann.  Rept.     59:  13-23.     1911. 

67.  Wilder,  H.  J.     U.  S.  D.  A.  Bui.  140.     1915. 


674  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

GLOSSARY 

Adiabattc. — A  curve  exhibiting  variations  of  pressure  and  volume  of  a  fluid  when 

it  expands  without  receiving  or  losing  heat. 
Adsorption. — The  adhesion  of  molecules  of  gases  or  dissolved  substance  to  the  sur- 
faces of  solid  particles;  distinguished  from  absorption,  which  is  not  a  surface 
phenomenon. 
Aitionomic. — As  referred  to  parthenocarpy,  the  ability  to  develop  parthenocarpic 

fruits  only  in  response  to  some  stimulus  external  to  the  ovary. 
Akene. — Dry,  unilocular,  indehiscent  fruit,  seed-like  in  appearance,  as  in  the  straw- 
berry. 
Alkali. — (1)  In  chemistry,  a  base;  (2)  as  applied  to  soils,  salts  present  in  amounts 
harmful    to    plants,    chiefly    sodium    chloride,    sodium    sulfate    and    sodium 
carbonate. 
Antagonism. — Of  salts,  a  mutual  counteraction  of  their  influence  on  cell  permeability. 
Arginine. — A  basic  amino-acid  which  is  a  product  of  protein  digestion. 
Autocatalysis. — A  process  of  catalysis  where  the  catalytic  agent  is  an  end  product 

of  the  reaction  catalyzed. 
Autogamy. — When  a  flower  is  fertilized  by  its  own  pollen. 
Autonomic. — As   referred   to   parthenocarpy,    the  ability   to  set  fruit  without  the 

stimulus  resulting  from  pollination. 
Barren. — Unproductive. 

Breba. — One  of  the  crops  of  the  pistillate  fig  tree,  the  first  to  mature  in  the  spring. 
Caprifig. — The  wild  or  "male"  fig,  the  uncultivated  form. 
Chemotropism.— A  bending  or  turning  in  response  to  a  chemical  stimulus. 
Chlorosis. — A  diseased  condition  shown  by  loss  of  green  color. 
Choline. — An  amine  arising  as  one  of  the  products  of  lecithin  decomposition. 
Colloid. — A  state  of  a  substance  where  the  units  are  very  large  molecules  or  molecule 
complexes.     Colloids  diffuse  slowly  or  not  at  all  through  plant  or  animal  mem- 
branes. 
Compatibility. — (1)  Of  sex  cells,  the  ability  to  unite  and  form  a  fertilized  egg  that 
can  grow  to  maturity.     (2)  Congeniality  as  determined  by  the  degree  of  success 
of  the  union  between  stock  and  cion. 
Coulure. — The   failure   of    blossoms    to    set,    resulting   in   a   premature   drop.     Cf. 

millerandage. 
Court-noue. — A  physiological  disturbance  of  the  grape  manifested  by  short  nodes. 
Creatine. — A  nitrogenous  compound  readily  converted  into  creatinine. 
Creatinine. — A  basic  nitrogenous  compound  occuring  naturally  in  muscle  tissue  and 

urine. 
Cumarine. — An   organic   compound   with   vanilla-like  odor   known   as   tonka   bean 

camphor. 
Dichogamy. — Insuring  cross  fertilization  by  the  sexes  being  developed  at  different 

times. 
Dicliny. — Male  and  female  organs  separate  and  in  different  flowers. 
Dihydroxy-stearic  Acid. — A  double  hj^droxide  of  a  common  fatty  acid. 
Dimorphism. — Presenting  two  forms,  as  long  and  short  growths  or  permanent  and 

deciduous  branches. 
Dioecious. — Unisexual,  the  male  and  female  elements  in  different  individuals. 
Disaccharide. — A  compound  sugar  yielding  two  simple  sugars  on  hydrolysis. 
Dormant. — Applied  to  buds  when  they  are  not  actively  growing  and  to  plants  when 

they  are  not  in  leaf. 
Emasculation. — The  artificial  removal  of  the  stamens  from  the  flower  before  they 
dehisce. 


GLOSSARY  675 

Embryogenic. — Pertaining  to  the  development  of  the  embryo. 

Embryo  Sac. — The  cell  in  the  ovule  in  which  the  embryo  is  formed. 

Endocarp. — The  inner  layer  of  the  wall  of  a  fructified  ovary. 

Endosperm. — The  nutritive  material  stored  within  a  seed,  originally  deposited  within 

the  embryo  sac. 
Ezocarp. — The  outer  layer  of  the  wall  of  a  fructified  ovary. 
Extine. — The  outer  coat  of  a  pollen  grain. 

Fasciation. — A  diseased  condition  resembling  the  growth  of  several  stems  into  one. 
Fecundation. — The  fusion  of  two  gametes  to  form  a  new  cell. 
Fecimdity. — The  ability  of  flowers  to  produce  seeds  that  will  germinate. 
Fertility. — (1)  Of  flowers,  the  capacity  of  producing  seeds  that  will  germinate;  (2) 

of  soils,  the  crop  producing  power. 
Fertilization. — (1)  The  fusion  of  two  gametes  to  form  a  new  cell;  (2)  the  application  of 

fertilizers. 
Frenching. — A  disease  characterized  by  loss  of  color  in  leaves  between  the  veins. 
Fruitfulness. — The  capacity  of  producing  fruit. 
Fruit   Setting. — A   development  of  the  ovary  and   adjacent   tissues  following   the 

blossoming  period. 
Gamete. — A  miisexual  cell  which  must  fuse  with  another  gamete  to  produce  a  new 

individual. 
Glucosides. — Compounds  that  yield  sugar  and  some  other  substance,  usually  aro- 
matic, on  hydrolysis. 
Guanine. — A  basic  nitrogenous  compound  related  to  uric  acid;  one  of  the  purines. 
Gynaeceum. — The  pistil  or  pistils  of  a  flower. 
Hermaphrodite. — A  flower  with  both  stamens  and  pistils. 

Heterostyly. — The  presence  of  styles  of  two  or  more  forms  or  two  or  more  lengths. 
Heterotypic. — Reduction  division  of  a  cell. 

Histidine. — A  basic  amino-acid  which  is  a  product  of  protein  digestion. 
Homotypic. — As  applied  to  cell  division,  involving  the  usual  process  of  karyokinesis. 
Hydrolysis. — Chemical  splitting  by  taking  up  the  elements  of  water. 
Hygroscopic  Coefficient. — The  percentage  of  soil  water  retained  in  contact  with  a 

saturated  atmosphere  and  in  the  absence  of  any  other  source  of  moisture. 
Hypoxanthine. — A  basic  nitrogenous  compound  related  to  uric  acid;  one  of  the 

purines. 
Imbibition. — The  process  of  absorption,  usuall}^  by  a  solid. 
Imperfect. — In  flowers,  unisexual. 
Impotence. — Inability  to  produce  functional  gametes  of  the  one  sex  or  the  other; 

sometimes  used  in  a  more  general  sense  to  denote  sterility. 
Inconjpatibility. — Of  sex  cells,  the  inability  to  unite  and  form  a  fertilized  egg  that  can 

grow  to  maturity. 
Interfertility. — The  ability  of  one  variety  to  set  fruit  and  produce  seeds  that  will 

germinate  when  poUenized  by  another  variety. 
Interfruitfulness. — The  ability  of  one  variety  to  set  and  mature  seed-containing  or 

seedless  fruit  when  pollenized  by  another  variety. 
Intersexualism. — Sex  intergrades;  a  term  referring  to  the  varying  degrees  of  develop- 
ment of  the  two  sex  organs  in  the  same  plant;  relative  maleness  or  femaleness 

of  the  plant. 
Intersterility. — Inability  of  one  variety  when  pollenzied  by  another  variety  to  set 

fruit  and  produce  seeds  that  will  germinate. 
lutine. — The  inner  coat  of  a  pollen  grain. 
June  Drop. — The  abscission  of  partly  developed  fruit  (often  occurring  in  June). 


676  FUNDAMENTALS  OF  FRUIT  PRODUCTION 

Latent  Bud. — A  bud,  usually  concealed,  more  than  one  year  old,  which  may  remain 

dormant  indefinitely  or  may  develop  under  certain  conditions. 
Lecithin. — A  fat-soluble  compound  containing  nitrogen  and  phosphorus. 
Locule. — The  cavity  of  an  anther  or  ovary. 
Mamme. — One  of  the  crops  of  the  caprifig  or  "male"  fig,  the  first  to  mature  in  the 

spring.     The  fruits  of  this  crop  winter  over  as  comparatively  large  specimens. 
Mammoni. — One  of  the  crops  of  the  caprifig  or  "male"  fig,  which  sets  in  June  and 

matures  in  late  summer. 
Millerandage. — A  condition  in  the  grape  where  the  ovary  persists  but  the  seeds 

remain  small  or  do  not  attain  usual  size;  produced  by  conditions  similar  to  tJiose 

that  lead  to  coulure. 
Monoecious. — The  stamens  and  pistils  in  separate  flowers  but  borne  on  the  same 

individual. 
Nucleic  Acid. — Phosphorus-containing  acids,  usually  combined  with  protein  in  all  cell 

nuclei. 
Nucleins. — Phosphorus-containing  compounds  of  nucleic  acid  with  protein. 
Osmosis. — Diffusion  through  a  membrane. 

Parthenocarpy. — The  production  of  fruit  without  true  fertilization. 
Parthenogenesis. — The  development  of  the  unfertilized  egg  into  the  usual  product  of 

fertilization  without  a  preceding  union  of  gametes. 
Pedicel. — The  support  of  a  single  flower  of  an  inflorescence. 
Peduncle. — The  support  of  an  inflorescence  or  a  flower  stalk. 
Pentosan. — A  polysaccharide  that  yields  five-carbon  sugars  on  hydrolysis. 
Perennation. — A  lasting  state,  referring  particularly  to  the  persistance  of  fruit  long 

after  its  usual  season  of  maturity. 
Perfect. — Hermaphrodite  flowers. 
Picoline. — A  basic  derivative  of  pyridine. 
Pollination. — The  placing  of  pollen  on  the  stigmatic  surface. 
Pollinium. — A  pollen  mass  consisting  of  all  the  pollen  grains  of  an  anther  locule. 
Polyembryony. — The  production  of  more  than  one  embryo  in  an  ovule. 
Polygamo-dioecious. — With     hermaphrodite     and    unisexual    flowers    on    different 

individuals  of  the  same  species. 
Polygamous. — With  hermaphrodite  and  unisexual  flowers. 
Polysaccharide. — A   carbohydrate  which   yields   a  large  but   indefinite  number  of 

simple  sugars  on  hydrolj^sis;  usually  colloids. 
Polyterpenes. — Compounds  which  yield  an  indefinite  number  of  simple  hemiterpene 

units  on  distillation;  ex.  caoutchouc,  balata. 
Profichi. — One  of  the  crops  of  the  caprifig  or  "mele"  fig,  the  second  to  mature  in  the 

spring.     The  fruits  of  this  crop  appear  as  small  buttons  in  the  late  fall  or  early 

winter. 
Proliferation. — A  rapid  and  repeated  production  of  new  parts,  as  the  formation  of 

leafy  parts  from  floral  parts. 
Protandry. — The  pollen  being  discharged  before  the  pistils  are  receptive. 
Protogyny. — The  pistils  receptive  before  the  anthers  have  ripe  pollen. 
Pseudo-hermaphrodite. — Functional  unisexuality  in  the  presence  of  apparently  well 

developed  stamens  and  pistils. 
Purines. — A  group  of  nitrogenous  organic  compounds  such  as  uric  acid,  xanthine  and 

caffein. 
Pyridine. — A  nitrogenous  base  which  is  the  nucleus  of  many  organic  compounds,  for 

example  nicotine. 
Pyrimidines. — A  group  of  basic  nitrogenous  compounds  related  to  the  purines  and 

found  as  products  of  nucleic  acid  cleavage. 
Quinone. — An  oxidation  product  of  benzene. 


GLOSSARY  677 

Respiration. — Gaseous  exchange  \)y  which  the  plant  absorbs  oxygen  and  gives  off 

carbon  dioxide. 
Respiratory  CoeflScient. — The  amount  of  carbon  dioxide  given  off  divided  by  the 

amount  of  oxygen  used  in  respiration. 
Salicylic    Aldehyde. — An    oxidation    product    of    sahcin    giving    the    fragrance    to 

meadow-sweet. 
Somaplasm. — The  protoplasm  other  than  the  germplasm. 

Sod  Culture. — A  method  of  orchard  soil  management  in  which  a  permanent  perennial 
crop  is  grown  between  the  trees,  mowed  once  or  twice  during  the  growing  season 
and  then  allowed  to  remain  on  the  ground.     A  limited  area  around  the  trees  is 
hoed,  spaded  or  otherwise  tilled. 
Sod  Mulch. — A  method  of  orchard  soil  management  in  which  a  permanent  perennial 
crop  is  growTi  between  the  trees,  mowed  once  or  twice  during  the  growing  season 
and  then  allowed  to  remain  on  the  ground. 
Sporogenous. — Producing  spores. 
Sporophyte. — The  plant  in  the  alternating  life  cycle  arising  from  a  fertilized  egg  and 

producing  spores. 
Sterility. — The  inability  to  produce  seeds  that  will  germinate. 
Supercooling. — Cooling  below  the  freezing  point  without  solidification. 
Temperature  Inversion. — A  rise  in  temperature  with  increasing  distance  from  the 

ground,  up  to  a  certain  height. 
Tetrad. — A  group  of  four  cells  such  as  the  pollen  grains  derived  from  one  spore  mother 

cell. 
Torus. — (1)  The  receptacle  of  a  flower,  part  of  the  axis  on  which  the  flower  parts  are 

inserted;  (2)  the  thickening  in  the  center  of  the  membrane  in  bordered  pits. 
Trimorphism. — Heterogomy,  or  with  long-,  short-,  and  mid-styled  flowers. 
Vacuole.— In  cells,  the  cell  sap  surrounded  by  protoplasm. 
Vanillin. — An  aromatic  compound,  the  fragrant  constituent  of  vanilla. 
Wilting  Coefficient. — The  percentage  of  moisture  in  the  soil  when  permanent  wilting 

of  plants  takes  place. 
Xanthine. — A  basic  nitrogenous  compound  related  to  uric  acid;  one  of  the  purisen. 
Xenia. — The  direct  influence  of  foreign  pollen  on  the  part  of  the  mother  plant  that 
develops  into  endosperm. 


PROPERTY  UBRAR7 

fl.  C.  State  College 


INDEX 


(Principal  discussions  are  in  bold  face  type) 


Abortion,  embryo,  526-S26 

embryo  sac,  495,  514,  521 

ovary,  487 

pistil,  484,  495,  504,  507,  511 

pollen,  478,  496-498,  507,  511-514 
Absorption,  18-22 

nitrogen,  130 

relation  to  concentration,  105 

relation  to  transpiration,  127 

selective,  126 
Acclimatization,  241 
Acidity  of  soil,  see  Soil  Reaction. 
Acid  tolerance  of  fruits,  118,  226 
Adsorption,  49,  255-260 
Aeration  of  soil,  126 
Age  and  fruit  setting,  614 
Air  drainage,  346-349,  643-652 
Alkali,  see  Concentration,  Soil  Reaction. 
Almond,   composition,    101,    138,    144,    149,    152, 
156,  160 

frost  injury,  359 

fruit-bud  formation,  187 

fruiting  habits,  402 

fruit  setting,  500,  542 

geography,  621 

pruning,  465 

soils,  657 

stocks,  553,  559,  564,  587,  601 

varietal  differences,  542 

water  requirements,  3,  16 

winter  injury,  291 
Alternate  bearing,  see  Fruiting  Habits. 
Altitude,  621 

see  Elevation. 
Aluminum,  in  plant  tissues,  160 

in  soils,  663-665 
Ammonium,  106 
Antagonism,  126 
Antipodals,  477 

Apple,  composition,  4,  5,  102-104,  133-138.  141- 
158,  254,  275,  319,  320 

cultivation,  66,  71,  77 

fertilizers,  206-217 

frost  injury,  359-362,  364,  381 

fruit-bud  formation,  186-192 

fruit  development,  530,  .531,  534 

fruiting  habits,  399,  4.")7-461 

fruit   setting,    .500,    503-505,    .509,    511,    518, 
521,  531,  640 

geography,  612,  614,  619-620,  624-628 

irrigation,  71,  73 

physiological  disturbances,  79,  83,  88-96 

propagation,  B89-696 


679 


Apple,  pruning,  408-433,  439-447,  450-453,  467- 
461 

root  distribution,  S6-6J,  581 

soils,  660-662,  666,  668-670 

stocks,  312,  316,  653-.554,  568-559,  562, 
565-567,  571-578,  581,  588-,592,  599. 
601 

temperature  requirements,  238-248,  624-628 

varietal  and  group  differences,  86,  190,  207, 
242-244.  254,  271,  319-322,  362,  422- 
424,  430,  441-443,  540,  581,  588,  594. 
624-626,  669 

water  requirements,  3,  7,  16 

winter  injury,   25,5-256,   261,   267-271,   279, 
291,  304,  312,  318-322 
Apricot,  composition,  138,  144,  149,  156 

frost  injury,  359-360 

fruiting  habits,  402 

fruit  setting,  519,  543 

geography,  621 

physiological  disturbances,  95 

pruning,  465 

stocks,  556,  575 

temperature  requirements.  245 

water  requirements,  3,  8.  10,  16 

winter  injury,  291 
Arsenical  poisoning,  196 
Aspect,  see  Slope. 
Assimilation,  161-166 
Atmospheric  humidity,  see  Humidity. 
Autogamy,  480 
Availability,  107-108 

iron,  109,  116-117 

nitrogen,  109 

phosphorus,  108,  116 

sulfur,  109 

water,  16,  47-49 
Axial  row,  477 
Azarole.  see  Hawthorn. 


Bark  splitting,  300 

Barrenness,  see  Fruitfulness. 

Bearing  habits,  see  Fruiting  Habits. 

Biennial  bearing,  see  Regularity  of  Bearing. 

Bitter-pit,  93,  195,  197 

Blackberry  (and  Dewberry),  composition.  4,  150 

fertihzers,  207 

fruit-bud  formation,  188 

fruiting  habits,  402,  467 

fruit  setting,  498-500.  544 

geography,  626,  634 

pruning,  453,  467 

soils,  118 


680 


INDEX 


Blackberry,   varietal   and  group  differences,  332- 
330,    498 

winter  injury,  315,  332-336 
Black-end,  94 

Blossoming  season,  342-346,  365-369 
Blueberry,  fruit-bud  formation,  403 

geography,  618 

soils,  118,  657,  662 


Calcium,  antagonjpm,  126 

deficiencies,  199 

displacement,  106 

in  fertilizers,  110,  157.  201-202,  221,  226 

and  nitrification,  110 

in  organic  compounds,  154 

in  plant  tissues,  101-104,  127,  154-166 

relation  to  chlorosis,  116 

in  soils,  156-157,  222,  663-605 
Carbohydrates,  167-168 

in  plant  tissues,  167,  171-176 

relation  to  fruit-bud  formation,  181-186 

relation  to  pigment  formation,  180 

storage,  170,  182-183 

synthesis,  167 

translocation,  167-176,  199,  434-435,  451 

utilization,  176-180,  184,  199,  451 
Carbon  assimilation,  162-166 
Carotin,  164 
Chalaza,  477 

Cherry,   composition,   4,    102-103,    132-133,    138, 
140-141,    144-146,    149-150,    154-156 

frost  injury,  359-360 

fruit-bud  formation,  188 

fruiting  habits,  401,  464 

fruit  setting,  486,  500-501,  543 

geography,  612,  620-621,  620 

physiological  disturbances,  95 

pruning,  410,  464-466 

root  distribution,  62 

stocks,  248,  313,  553-554,  560,  562,  566,  568, 
582,   585 

temperature  requirements,  326,  628 

varietal  and  group  differences,  313,  326-328, 
401,  486,  543 

water  requirements,  8,  16 

winter  injury,  288,  291,  297-298,  313,  326- 
328 
Chestnut,  composition,  4,  101,  102,  138,  144,  149, 
152,  153,  156,  158 

fruiting  habits,  404 

stocks,  570 

winter  injury,  292 
Chinquapin,  see  Chestnut. 
Chlorine,  159,  199 
Chlorophyll,  164-165 
Chlorosis,  85,  116-117,  199,  569,  662 
Cion,  influence  on  stock,  579-683 

rooting,  594 

selection,  603-606 
Citrus  fruits,  composition,  150,  152 

geography,  621 

physiological  disturbances,  106,  116,  120 

propagation,  590,  596 

soils,  660,  669 


Citrus  fruits,  stocks,  582,  587 

water  requirements,  3 

winter  injury,  272 

see  Orange. 
Climate,      see     Temperature,      Winter     Injury, 

Precipitation. 
Clouds  and  frost,  341 
Concentration  of  sap,  see  Sap  Density. 
Concentration     of    soil    solution,     injuries    from 
"alkaU,"  119-121,  190 

requisites  for  absorption,  105 

and  root  distribution,  64 

tolerance  of  different  plants,  118-119 
Congeniality  of  grafts,  662-557 
Copper  poisoning,  195 
Cork,  89 

Coulure,  454,  497,  514 
Cover  crops,  acid  tolerance,  118 

and  nitrogen  fixation,  114-115 

and  soil  moisture,  34-35,  41-46,  279-281 

and  soil  temperature,  307 

toxic  action,  124 

and  winter  injury,  271,  279-281,  310-312 
Cranberry,  85,  188,  202,  349-366,  618 
Cross  sterility,  501 
Crotch  and  crown  injury,  271-274 
Cultivation,  31,  38-39 

and  frost  danger,  355 

and  fruit  setting,  81 

and  nitrification,  111-114 

and  root  distribution,  63 

an  1  run-off,  32 

and  soil  temperature,  306-307 

and  vegetative  growth,  66 

and  water  requirement,  10 

and  winter  injury,  269,  270,  279,  289 
Cup-shake,  300 
Currant,  composition,  4,  150,  258 

fruit-bud  formation,  188 

fruiting  habits,  402 

fruit  setting,  544 

geography,  618 

physiological  disturbances,  84 

pruning,  466 

temperature  requirements,  628 

varietal  and  group  differences,  335,  466 

winter  injury,  315,  335 
Cuttings,  propagation  by,  689-695 


Date  palm,  242,  487 

DefoUation,  80 

see  Summer  Pruning. 

Degeneration,  see  Abortion. 

Dehorning,  427-429 

Depth  of  freezing,  see  Soil  Temperature. 

Depth  of  rooting,  see  Root  Distribution. 

Dewberry,  see  Blackberry. 

Dewpoint  and  frost,  341,  370 

Dieback,  88,  91-92,  195 

Dioecious  plants,  490-492 

Disease,  extent  of  injury,  2 
fruit  setting,  518 
susceptibility,  75,  568-569 


INDEX 


681 


Disease,  see  Parasites,  Physiological  Disturbances. 

Displacement,  106 

Distance  of  planting,  see  Planting. 

Double  fertilization,  477,  482 

Double  working,  601-603 

Drought  injury,  2,  14-16,  41,  86-96,  257.  274 

Dwarfing,  432-434,  557-560,  575,  579-580,  597 


Egg  apparatus,  477 

Elder,  400 

Elevation,  339,  346-351,  643-648 

Embryo,  abortion,  525-526 

formation,  482 
Embryo  sac,  477 
Endosperm,  482 
Enzymes,  166 

Evaporation,  45,  281-282,  654 
Exanthema,  see  Dieback 
Exposure,  see  Slope. 


False-blossom,  85 
Fasciation,  84,  416 
FertiUty,  487,  606,  510 

see  Fruitfulness,  Fruit  Setting. 
Fertilization,  481 
Fertilizers,  151,  222-226 

excessive  applications,  119 

fruit  setting,  510 

indirect  effects,  218-221 

lime,  221 

methods  of  action,  200 

nitrification,  110 

nitrogenous,  204-217,  510 

orchard  requirements,  200-203,  667 

phosphorus,  218-219 

protective  action,  123 

soil  temperature,  307 

sulfur,  219,  226 

time  of  application,  227-228 

water  requirement,  10,  12 

winter  injury,  289 
Fig,  composition,  138,  144,  149,  156,  158 

fruit  development,  533-534 

fruiting  habits,  404 

fruit  setting,  491,  493,  513,  623-624 

geography,  621 

physiological  disturbances,  83 

water  requirements,  3,  16 
Filbert,  188,  403,  493 
Frenching,  106 

Freeze  and  frost  distinguished,  338 
Frost,  crack,  298-300 

danger,  342-356,  366 

formation,  337-341,  351,  370 

injury,  2,  358-365,  380-381 

penetration,  see  Soil  Temperature. 

prediction,  369-373 

protection,  373-380 
Fruit-bud  formation,  181-193,  413-414,  419-426, 

451-452,  570-572 
Fruit  development,  525,  629-636 


Fruitfulness,  487 

age  and  vigor,  614 
•    compatibility,  600-602,  507 

dichogamy,  492-494,  512 

evolutionary  tendencies,  489-498 

external  factors,  509-520 

genetic  factors,  489,  498-502 

grafting,  510 

heterostyly,  492 

hybridity,  499 

intersexualism,  490-492 

locality,  510-512 

moisture  supply,  516 

nutrient  supply,  609 

nutritive  conditions,  604-607 

physiological  factors,  489,  502-507 

pistil  abortion,  494-495,  507 

pollen  abortion,  496-498,  507,  512 

pollen  tube  growth,  481,  502 

season,  612-614 

temperature,  514-616 

time  of  pollination,  503 
Fruiting  habits,  397-406 
Fruit-pit,  89,  93 
Fruits  classified,  475 
Fruit  setting,  483,  487 

disease,  518 

humidity,  80-82,  516-.517 

individual  fruits,  640-646 

June  drop,  484-487 

nitrogenous  fertilizers,  209-211 

pinching,  454 

ringing,  436 

spraying,  519 

stimulating  agents,  521-526 

wind,  618 
Fruit  splitting,  81 
Fruit  zones,  612-621 
Funicle,  477 


Girdling,  see  Ringing. 
Gooseberry,  composition,  4,  150 

fruit-bud  formation,  188 

fruit  development,  529-530 

fruiting  habits,  402 

fruit  setting,  544 

geography,  618 

pruning,  466 

stocks,  553,  568 

temperature   requirements,   243,   248,   628 

winter  injury,  315,  335 
Grafting,  552-557,  600 
Grape,  composition,  4,  138-139,  143-144,  152-159 

coulure,  454,  457,  5l9,  572 

fertilizers,  226 

frost  injury,  350 

fruit-bud  formation,  188 

fruit  development,  532 

fruiting  habits,  402,  468 

fruit  setting,   436,   484,   49f}-499,   502,   509- 
514,  518,  521,  643,  572 

geography,  612,  615-616,  620-624,  633 

irrigation,  330 

millerandage,  572 


682 


INDEX 


Grape,    physiological     disturbances,    80,    86-87, 
117,  569 

pinching,  454 

propagation,  591 

pruning,  438,  453-454,  467-471 

ringing,  436 

root  distribution,  582,  591 

soils,  658-662,  668 

stocks,  553,  555,  559,  560,  563-582,  586-588 

temperature  requirements,  241-247,  623-624 

training,  470 

varietal  and  group  differences,  244,  314,  330, 
331,  470,  496,  526,  543 

water  requirements,  3,  16 

winter  injury,  314,  329-331 
Gummosis,  568 


Hail  injury,  2 

Hardiness,     see     Frost     Injury,    Winter    Injury, 

Winter  Killing. 
Haw,  400 
Hawthorn,  400 
Heading  back,  see  Pruning. 
Heating,  see  Orchard  Heating. 
Heat  units  and  requirements,  336-247 
Heeling-in,  19 
Heterostyly,  492,  502 
Hickory,  405,  620 
Humidity,  fruit  setting,  80-83,  516 

geography  of  fruit  production,  631 

growth,  78-82 

russeting,  79 

winter  injury,  274 
Hybridity  and  unfruitfulness,  499 
Hygroscopic  coeflScient,  13 


Immaturity,  see  Winter  Injury,  Winter  Killing. 

Impotence,  478,  494-498 

Incompatibility,  fruitfulness,  600-602,  507,  511 

grafts,  562-667 
Integuments,  477 

Interfertility,  see  Fertility,  Fruitfulness. 
Intercrops,  40-41,  81,  124 
Interfruitfulness,  601 
Intersexualism,  490-492,  499 
Inversion     of     temperature,     see     Temperature 

Inversion. 
Iron,  availability,  109,  116-117 

deficiencies,  116,  199 

in  fertilizers,  117,  668 

in  plant  tissues,  101,  161-162 

in  soil,  663-665 

solubility,  152 
Irregular  bearing,  see  Regularity  of  Bearing. 
Irrigation,  8 

"alkali,"  121 

color  and  quality  of  fruit,  74-76 

frost  danger,  354 

fruit  size,  71 

vegetative  growth,  66 

winter  injury,  278,  335 


Jonathan  spot,  93 

Jujube,  404 

Juneberry,  400 

June  drop,  see  Fruit  Setting. 


K 


Killing  back,  268-271 
see  Dieback. 


Land  values,  638 
Latitude,  237-239,  342-343 

Layering,  593 

Leaf  pigments,  164 

Light,  carbohydrate  manufacture,  183 

frost  injury,  262 

fruit-bud  formation,  183 

fruit  setting,  516 

nitrogen  elaboration,  130 

phosphorus  elaboration,  138 

transpiration,  27 

water  requirement,  11 
Lime,  see  Calcium. 
Lithiasis,  95 
Location,  frost  danger,  342-346 

fruit  setting,  610-612,  515 

selection  of,  635,  637-639 
Loquat,  399,  553,  564.  575,  621 

M 

Macrosporangium,  473 
Macrospore,  477 
Magnesium,  antagonism,  126 

deficiencies,  199 

displacement,  106 

excesses,  195 

in  plant  tissues,  101-102,  162-163 

in  soil,  663-665 
Manure,  see  Fertilizers. 
Manganese,  in  plant  tissues,  160 

in  soil,  117,  197,  663-665 
Maturity,  272 

see  Winter  Injury,  Winter  Killing. 
Medlar,  400,  555 
Micropyle,  477 
Microsporangium,  473 
Microspore,  478 

Moisture,  see  Humidity,  Soil  Moisture,  Water. 
Monoecious  plants,  490-492 
Mulberry,  404 
Mulching,  34,  307,  315,  334,  353,  368 


N 


Nitrate  of  soda,  see  Fertilizers. 
Nitrification,  110-112 
Nitrogen,  absorption,  130 

availability,  109-110,  222-224 

deficiencies,  198 

elaboration,  130 

excesses,  195 

fixation,  114-116 

in  fertilizers,  123,  201-202,  222-224 


INDEX 


683 


Nitrogen,  in  plant  tissues,  131-138 

relation    to    fruit-bud    formation,     181-186, 
207-208 

relation  to  fruit  coloration,  212 

relation  to  fruit  composition,  215-216 

relation  to  fruit  size,  209-212 

relation  to  fruit  setting,  209,  510 

relation  to  season  of  maturity,  216 

relation  to  vegetative  growth,  204-207 

relation  to  winter  injury,  289 

relation  to  yield,  212-215 

in  soil,  113,  222,  663-605 

storage,  135,  138 

translocation,  131-133 
Notching,  see  Ringing. 
Nubbins,  495 
Nucellus,  477,  483 
Nursery  stock,  19,  316,  696-606 

see  Stocks. 


(Edema,  84 

Olive,  composition,  138,  144,  149,  153,  156,  158, 

159 

fertilizers,  216 

geography,  617 

planting  distance,  8 

propagation,  590 

root  distribution,  63 

soils,  662,  665 

temperature  requirements,  242 

water  requirements,  8,  16,  77 
Orange,    composition,    138,    144,    149-153,    156, 
158-159 

fertilizers,  216 

fruit  setting,  81,  495,  498 

physiological  disturbances,  120 

root  distribution,  62,  64 

soils,  118 

stocks,  554,  557,  562-563.  572,  575,  580,  587- 
588 

water  requirements,  7 

see  Citrus  Fruits. 
Orchard  heating,  373-880 
Osmosis,  20,  105 
Ovary,  473,  475,  487 
Ovule,  476-476 


Papaya,  491,  515 

Parasites  and  geography  of  fruit  production,  633 

see  Diseases. 
Parenchymatosis,  84 
Parthenocarpy,  487,  621-629 
Parthenogenesis,  525 

Pathological  conditions,  see  Physiological  Distur- 
bances. 
Peach,  composition,  4,  138,  144,  148-150,  156,  287 

cultivation,  289 

fertilizers,  204,  208,  2H-212,  215-216,  289 

frost  injury,  359-362,  364,  366 

fruit-bud  formation,  187 

fruiting  habits,  401,  461 

fruit  setting,  542 

geography,  620-623,  634 


Peach,  irrigation,  71 

propagation,  589 

pruning,    288,   325-326.   410-413.    416,    441, 
461-464 

soils,  657,  665,  670 

stocks,  555,  562,  576,  580,  587,  599 

temperature    requirements,    238-240,    246- 
246,  248,  622 

thinning,  290 

varietal  and  group  differences,  285-291,  326, 
362 

water  requirements,  3,  6,  16 

whitewashing,  291 

winter  injury,  267,  269,  286-292,  298,  312, 
323-326 
Pear,  composition,  4,  103-104,  133,  138,  141,  144, 
149,  152-156,  158 

frost  injury,  359,  364,  380 

fruit-bud   formation,    187,    192 

fruit  development,  525,  529,  535 

fruiting  habits,  399 

fruit  setting,  500,  518,  641,  572 

geography,  248,  612,  614,  619-621 

irrigation,  74 

physiological  disturbances,  84,  94,  95 

propagation,  593 

pruning,    408-417,    419-433,    439-447,    450- 
453,  467-461 

soils,  657,  662 

stocks,  312,  553,  557,  566,  570,  572-575,  585, 
588,  601-  602 

varietal  and  group  differences,  323,  430,  541 

water  requirements,  3 

winter  injury,  312,  322-323 
Pecan,  fruiting  habits,  405 

fruit  setting,  493 

geography,  612,  620-621 

physiological  disturbances,  93,  224 

winter  injury,  269 
Pedigreed  plants,  603-606 
Pentosans,  50.  167.  168-177,  267-260 
Percolation,  see  Seepage. 
Perennation,  527 
Perisperm,  483 
Persimmon,  fruit  development,  530,  532-634 

fruiting  habits,  404 

fruit  setting,  490,  514,  545 

stocks,  559 
Phosphorus,  availability,  108,  116,  225 

elaboration,  138 

in  fertilizers,  123,  202,  218-219 

in  plant  tissues,  101-102,  138-144 

in  soil,  225,  663-665 

solubility,  225 
Phyllody,  84 
Physiological  disturbances  ,  83-94,   106,   195-197, 

224 
Pigments,  164,  180 
Pinching,  332-333,  453-455,  510 
Pineapple,  composition,  150,  153,  158,  159 

fertilizers,  117 

physiological  disturbances,  116-117 

soils,  116-117,  658,  662-666 
Pistil  abortion,  484,  .504,  509,  511 
Placenta,  477 
Planting,  depth,  315 


684 


INDEX 


Planting,  distances,  8,  59 

season,  19,  209,  316 
Plum,  blossoming  season,  342 

composition,  4,  102,  103,  132,  133,  138-141, 
144,  149,  150,  153-159 

frost  injury,    359,   362 

fruit-bud  formation,  187,  192 

fruiting  habits,  401 

fruit   setting,    484-486,   493,   495,    500,    504, 
505,  511,  642 

geography,  619,  620,  033,  634 

physiological  disturbances,  94,  95 

propagation,  589,  .590 

pruning,  410,  429,  440,  465 

root  distribution,  581 

soils,  668,  669 

stocks,  248,  314,  553,  555,  561,  564,  571,  580, 
581,  584,  586,  588,  602 

temperature  requirements,  238,  245 

varietal  and  group  differences,  285,  328,  329, 
362,  495,  542,  669 

water  requirements,  3,  8,  16 

wliitewashing,  291 

winter  injury,  255,  256,  273,  285,  314,  328- 
329 
Polar  bodies,  477,  482 
Pollen,  abortion,  478,  496-498,  509,  511-512 

carrying  agents,  639 

formation,  477-479 

germination,  480-481,  504 

specific  effects  on  fruit,  634-636 
Pollen  tube  growth,  481,  502,  503,  513,  515 
Pollination,  478,  503,  515,  638-640 
Polyembryony,  504 
Pomegranate,  401,  495,  657 
Potassium,  availability,  109 

deficiencies,  106,  198 

displacement,  106 

in  fertihzers,  123,  145,  201,  202,  225 

fruit  coloration,  145 

in  plant  tissues,  101,  102,  146-160 

in  soil,  146,  663-665 

replacement,  159 
Precipitation,  fruit  setting,  516,  517 

geography  of  fruit  production,  631-632,  654 

requirements  for  trees,  6-7 

vegetative  growth,  67-70 

winter  injury,  266,  270,  274-278 
Propagation,  see  Grafting,  Nursery  stock.  Stocks. 
Proliferation,  527 
Protandry,  492-494 
Protogyny,  492-494 
Prune,  see  Plum. 
Pruning,  388-471 

nutritive  conditions,  426,  510 

winter-injured  trees,  316,  326-326,  432 

winter  injury,  288 


Quince,  150,  187.  400,  542.  657 


Radiation,  338-340,  351,  373-374 

Rainfall,  see  Precipitation. 
Raphe,  477 


Raspberry,  composition,  4,  150,  258 

fertilizers,  207 

fruit-bud  formation,  188 

fruiting  habits,  402.  467 

fruit  setting,  544 

geography,  619 

irrigation,  335 

mulching,  335 

pruning,  332,  333,  453,  467 

soils,  118 

temperature  requirements,  628 

varietal  and  group  differences,  332-336 

winter  injury,  315,  332-336 
Regularity  of  bearing,  78,  406 
Respiration,  166 
Rest  period,  284-286,  292 
Ringing,  434-437,  506 
Root,  distribution,  64-64,  679-683 

killing,  22,  304,  312-316 

pruning,  19.  432-434 
Rosette,  91-92 
Rough  bark  disease,  85 
Run-off,  7,  32 
Russeting  of  fruit.  79,  381 


Sap  density  and  hardiness,  264,  257 

Scaly  bark  disease.  84 

Secondary  fertilization,  482 

Second  bloom,  191,  381,  415 

Second  growth,  70,  270 

Seedlessness,  198,  364,  487,  509,  621-627 

Seeds  and  fruit  development,  629-634 

Seepage,  7,  51.  52 

Selective  absorption,  126 

Self  fertility,  see  Fertility. 

Self   sterility,   see   Fertility,    Fruitfulness,    Fruit 

Setting. 
Setting  fruit  trees,  see  Planting. 
Sex  distribution,  490-492 
Shadbush,  400 
Shading,  1,  11.  291 

Sihcon  in  plant  tissues,  101,  102,  167-168 
Silver  leaf,  95 
Sites,  346-351,  663-655 
Slope,  639-643 

Smudging,  see  Orchard  Heating. 
Sodium,  106,  158-169,  663-665 
Sod-mulch,  32-38,  66,  111,  114,  124,  306.  352 

see  Soil  Management  Methods. 
Soil,  acidity,  see  Soil  Reaction. 

alkali,  see  Concentration. 

chemical  composition,  662-668 

crop  adaptation,  668-671 

fruit  setting,  509 

general  orchard  requirements,   666-688 

management   methods,   31-46,    62-64.    111- 
114.  306-307,  362-367 

mechanical  analyses,  658-661 

reaction,  116-118,  128,  223,  226,  662 

solubility,  107 

temperature.  247-248,  302-312,  640 

toxins,  122-126 

type  and  frost  danger,  351 

type  and  frost  penetration.  808 


INDEX 


685 


Soil  moisture,  47-50 

absorption,  21 

availability,  16,  47-49 

composition,  74 

cover  crops,  41-45,  279-281 

disease  susceptibility,  76 

evaporation,  282-284 

frost  danger,  363-366 

fruit-bud  formation,  185 

fruit  shape  and  color,  73 

fruit  size,  71 

fruit  setting,  516 

intercrops,  39-41 

movement,  61-63 

physiological  disturbances,  83-96 

residual  effects,  69,  73,  76-78 

root  distribution,  60-62 

root  killing,  22 

second  growth,  70 

soil  management  methods,  32-  38 

vegetative  growth,  22,  34,  66-71 

wilting  points,  16 

winter  injury,  274-284,  309-310 

yield,  34,  72-73,  76-78,  228 
Solubility  of  soil,  107 
Sour  sap,  see  Sunscald. 
Sphtting  of  fruit,  81 
Spraying  in  bloom,  619 
Starch,  synthesis,  167 

in  plant  tissues,  169,  173-174 

storage     and     translocation,    169-170, 
326 

see  Carbohydrates. 
Sterility,  see  Fertility,  Fruitfulness,  Fruit  Setting. 
Stooling.  593 

Stock,  influenced  by  cion,  579-683 
Stock,  influence  on  cion,  disease  resistance,  668- 
569 

form  660-661 

fruit  setting,  510,  572 

fruit  size,  672-574 

hardiness,  321,  566-567 

longevity,  578 

maturity,  562-566 

quality,  574-678 

stature,  567-560 

yield,  569-574 
Stocks,   congeniality  and   adaptability,   662-667, 


173, 


Stocks  for,  almond,  553,  5.59,  564,  587,  601 

apple,  553,  554,  558,  559,  562,  56.5-567,  5/1- 

578,   581,  588-592,  599,   601 
apricot,  556,  575 

cherry,  553,  554,  560,  562,  566,  568.  582,  585 
chestnut,  570 
gooseberry,  553,  568 
grape,    553,    555,    5.59,    560,    663-666,    567- 

569,  571-578,  580-582,  686-688 
loquat,  553,  564,  575 
medlar,  555 
orange,  5.54,   557,   562,   563,   567,   572,   575, 

580,  587,  588 
peach,  555,  562,  576,  580,  587,  599 
pear,  553,  557,  566,  570,  572-575,  585,  588, 

601,  602 
persimmon,  559 


Stocks,   plum,   553,   555,  561,  562,  564,  571,  574, 
580,  581,  584,  586,  588,  602 

walnut,  568,  588 
Strawberry,  composition,  153 

fertilizers,  205,  216,  221 

frost  injury,  361-363 

fruit-bud  formation,  188,  190 

fruit  setting,  487,  490,  495,  498,  510,  513,  544 

irrigation,  75 

mulching,  353 

soils.  118,  662,  666 

varietal  and  group  differences,  362,  363 
Stringfellow  root  pruning,  19 
Stripping,  see  Ringing. 
Submergence  and  root  killing,  22 
Sugars,  167-168,  174-179 

see  Carbohydrates. 
Sulfur,  availability,  109 

deficiencies,  199 

in  fertilizers,  151,  202,  219,  226 

in  organic  compounds,  150 

in  plant  tissues,  101,  102 

in  soil,  151,  663-665 
Summer  pruning,  26,  72,  439-453,  463 
Sunscald,  292-296 

Sunshine  in  fruit  growing  sections,  633 
Suspensor,  482 
Synergids,  477,  481 


Temperature,  234-236,  621-631 

and  assimilation,  165 

and  bodies  of  water,  628-630,  648-650 

critical  for  flowers,  358-363,  366 

critical  for  roots,  304,  312-316 

at   different   elevations,    346-351,    621,    630, 
64.3-648 

and  disease,  248 

and  fruit-bud  formation,  185 

and  fruit  setting,  614-616 

heat  units  and  requirements,  236-247,  617- 
630 

inversion,  339,  349-351,  376-378,  646-648 

local    variations,    663 

and  nitrification,  112 

of  plant  tissues,  276-278,  29.3-296,  340,  641 

effects   of  rapid   temperature   changes,   260- 
261,  296-300 

sheltered    and    exposed    thermometers,    293, 
340 

of  soil,  247-248,  302-312,  640 

influenced    by    soil    and    soil    management 
methods,  349-366 

and  transpiration,  27,  28 
Terminal  bud  formation,  68-70 
Thermal  belts,  646-648 
Thinning  and  winter  injury,  290 
Thinning  out,  see  Pruning. 
Tillage,  see  Cultivation. 
Tipburn,  87 
Topping,  4.53 
Toxins,  see  Soil  Toxins. 
Training,  391-396 
Transpiration,  23-28,  126,  449 
Transplanting,  see  Planting. 


686 


INDEX 


Transportation  facilities,  639 
Trunk  splitting,  298-300 
Tufting  of  carpels  and  seeds,  84 


U 


Unfruitfulncss,  see  Fruitfulness. 


Variegation,  569 
Verdant  zones,  646-648 
Virescence,  85 


Walnut,  composition,  4,  138,  144,  149,  152-159 
fruiting  habits,  405 
fruit  setting,  493 
geography,  620 
physiological  disturbances,  88 
stocks,  568,  588 
water  requirements,  3,  16 
winter  injury,  268 


Water,  absorption,  see  Absorption. 

adsorption,  see  Adsorption. 

conduction,  28-29,  276 
Watercore,  86 

Water  content,  plant  tissues,  4-6,  60,  275,  276, 
287,  294,  319,  320 

soil,  13-17,  49 
Water,    requirements,     1-13 

retention,  266-260,  274-276 
Whitewashing,  291,  296,  368 
Wilting  coefficient,  13-17 
Wind,  influence  on,  evaporation,  45,  281-284,  634 

frost,  341,  378,  379 

fruit  setting,  618 

transpiration,  26-27 

winter  injury,  273 
Windbreaks,  46,  81,  281-284,  652 
Winter  killing,  260-262,  296-300,  566-567 
Winter  injury,  264-278,  292-336,  651 


Xenia,  482 


